ISSN 0704-3716
Canadian Translation of Fisheries and Aquatic Sciences
No. 5597
Farming the Atlantic cod, Gadus morhua,
biological and economic realities
J.D. Dutil
Original title:
L'elevage de la morue franche, Gadus morhua:
realites biologiques et economiques
In: Rapport canadien à l'industrie sur les sciences halietiques et
aquatiques. 200. Mont-Joli, Québec: Direction des Sciences
biologiques, Ministère des pêches et des océans, 1989.
Original language:
French
Available from:
Canada Institute for Scientific and Technical Information
National Research Council
Ottawa, Ontario, Canada K1A 082
1993
Depastnnerd cd Fisheries
& Oceens
42 typescript pages
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TABLE OF CONTENTS
Page
'LIST OF TABLES
LIST OF FIGURES
vi
ABSTRACT/RESUME
ix
PREFACE
INTRODUCTION
1
PART I - ECONOMICS
WORLD SUPPLY
2
World catch
2
DEMAND
The importance of the United States market
Quebec
3
to
3
U.S. consumption trends
Consumption of seafood
Consumption of other sources of protein
3
4
4
United States market for cod filets
U.S. Inventories of cod filets
U.S. imports
Prices
5
5
6
6
Market for salted dried cod
7
THE POTENTIAL FOR COD FARMING IN QUEBEC
8
Microeconomic considerStions
10
I R.
al
iv"
'TABLE OF CONTENTS (continued)
Page
PART II -.COD BIOLOGY AND COD-REARING EXPERIMENTS
REPRODUCTION
12
Sexual maturation
12
Fertilization methods
12
••
EMBRYO DEVELOPMENT
LARVAE
13
• 14
Mortality
15
Growth
16
JUVENILES AND ADULTS
16
Distribution
16
Diet
17
Metabolism
Base ration
Ingestion and digestion
Food conversion ratios
18
19
19
20
Growth
21
Diseases
22
Parasites
23
DISCUSSION
24
•
REFERENCES
27
LIST OF FIGURES
Page
Figure
1
. Percentage distribution of cod catch among five main
cod-fishing nations in 1987 (figures for Canada
exclude Quebec)
2
2
Cod catch in main cod-fishing nations, 1980 to 1988
(Figures for 1988 are projections.)
2
3
Exports of cod from Quebec in 1987i by country of
destination
3
4
Exports of cod from Quebec in 1987,
category
3
5
Consumption of sea food in the United states
4
6
U.S. price indexes for four sources of protein,
1974-1987
4
7
U.S. consumption of four sources of protein, 1962
to 1988
5
8
End-of-month inventories of cod filets in the United
States
5
9
U.S. imports of cod filets, by country of origin,
for the first six months of 1986, 1987, and 1988
6
10
Effect of exchange rates on the monthly price for
cod filets (Canada/5 lbs/1-2). Prices are shown at
the January 1986 exchange rate (c) and current
exchange rates (v).
7
11
Effect of exchange rates on the monthly price for
cod filets (Iceland/5 lbs/1-2). Prices are shown at
the January 1986 exchange rate (c) and current
exchange rates (v).
7
12
Quebec exports of lightly salted cod, by country of
destination, 1987
8
by product
It
LIST OF FIGURES (continued)
Page
Figure
13
Quebec exports of lightly salted cod, by country of
destination, 1985 to 1987
8
14
Prices for lightly salted cod, Italy and the United
States, 1985 to 1988
8
15
Landings of cod in Quebec, 1984 to 1988
9
16
Dockside prices for cod taken by three size classes
of longliner in Quebec, 1984 to 1988
9
17
Seasonal variations in the price of frozen cod
filets on the Boston market (average price for each
calendar month, 1983 to 1988)
10
18
Fertility of eggs as a function of time kept in sea
water (from Davenport et al, 1981)
13
19
Length of incubation period as a function of
temperature, for larval stages LA, 1B, 2, 3, 4, and
5 (adapted from Thompson and Riley, 1984)
14
20
Length distribution of cod larvae with and without
swim bladders after 30 days (froi Howell, 1984).
Black bars on left represent larvae without
bladders; grey bars on right represent larvae with
bladders.
16
21
Distribution of cod less than one year old as a
function of salinity along the coasts of England in
September and October, 1970 to 1975 (from Riley and
Parnell, 1984)
17
22
Increase in oxygen consumption over time for a cod
fed to satiety. Points represent average consumption
over 24 hours. Meals are marked on the x axis.
(from Soofiani and Hawkins, 1982)
18
tl
LIST OF FIGURES (continued)
Page
Figure
23
Decrease in weight of food in stomach as a function
of number of hours since last meal, at 2°C and 10°C
(from Tyler, 1970)
20
24
Rate of growth in weight as a function of the
[initial?] weight of cod fed to satiety at 8.5°C
(Braaten, 1984)
22
1
11,
I
•
t
LIST OF TABLES
Page
Table
1
Estimated costs of producing saltwater fish in
floating cages in Europe and Atlantic salmon in
Canada
11
2
Summary of some biological characteristics
Atlantic cod at each stage of their life cycle
36
of
PREFACE
The aquacultural industry is experiencing tremendous growth, growth which could
have an enormous Impact on the market for marine products in the relatively near
future. If we wish to participate in this growth, we will have to overcome
certain problems Inherent in rearing organisms in cold water. These problems
include a short growing season and the presence of ice in winter. To solve these
problems, research will have to be done on new species offering the greatest
economià potential. Experiments in rearing the Atlantic cod have already been
conducted in Newfoundland and in northern Europe, and some fish farmers in
eastern Canada might want to consider raising this species. The staff of the
Economic Services and Aquaculture divisions of Quebec Region have prepared this
report to analyze the biological and economic factors that could affect the
successful rearing of this fish in Quebec.
0
1
INTRODUCTION
World demand for marine products is growing, but traditional fishing seems
unlikely to be able to satisfy it. Aquaculture appears to be the best
alternative. It already accounts for 12 per cent of the production of marine
products worldwide. In Quebec, though it has good potential, the aquaculture
industry is still quite modest: in 1988, it contributed only 2 per cent of the
volume of commercial production. And there was little diversity in the species
produced, which consisted solely of rainbow trout, brook trout, blue mussels,
and the Atlantic salmon.
To encourage growth in aquacultural production through diversification of the
species produced, this report examines the possibilities of rearing a salt-water
fish: the Atlantic cod, Gadus morhua. This report has four objectives:
- to determine whether current economic conditions in Canada and around
the world are favourable to cod farming;
- to present the results of experiments that have been done on rearing
Atlantic cod;
- to discuss those research results that may have implications for codrearing practices;
- to point out those areas where a lack of basic information could prevent
the expansion of an industry based on the rearing of Atlantic cod.
The cod is an indigenous species that tolerates a wide range of environmental
conditions (Scott and Scott, 1988), and work on propagating it dates back some
time. The first known attempts were made in Norway in 1865, when Sars collected
eggs fertilized in nature and incubated them in the laboratory. In the following
year, he succeeded in fertilizing eggs in the laboratory, using eggs and milt
collected from fish taken in the field. Following these tests, Norway opened
the Flodevigen hatchery. Other hatcheries were established around the same time
in the United States and in St Johns, Newfoundland. Annual production reached
200 million larvae in Norway and 2.5 billion in the United States (larvae were
raised to the point that they had developed swim bladders*). But these programs
never demonstrated their usefulness, and the American and Norwegian governments
discontinued them (at least on this scale) In 1952 and 1971, respectively.
al. for
Interested readers should consult Shelbourne (1964) and Solemdal et.
histories of cod rearing in the 19th and 20th centuries.
Thus the field of cod rearing is.still in its infancy, and this review will
convince the reader that many laboratories have already mastered the techniques
for fertilizing and incubating eggs and producing larvae. Since the purpose of
the hatcheries discussed above was to produce larvae to rebuild the stocks fished
in the Atlantic, little work was done on producing juvenile or commercial-size
cod on an industrial scale. Recently, however, some work has been done in this
area, in Norway using enclosed ponds (Rvenseth and Oiestad, 1984; Oiestad et.
al., 1985) and in Newfoundland using outdoor tanks (Williams and Riceniuk, 1986).
Yffere is also a commercial on-growing facility operating on a seasonal basis in
Newfonndland. In England, Rowell (1984) has succeeded in rearing cod from
fertilized eggs to weights of nearly half a kilogram, thus demonstrating the
* Translator's note: The phrase in parentheses is the meaning suggested by one
But this
of the authors (Richard Bailey) for the French term "vésiculges".
text
was
written
part
of
the
interpretation could not be confirmed, because this
for
deadline
this
by another of the authors, who was unavailable before the
translation.
')
2
feasibility of rearing cod in temperate climates. It should be noted that the
cod offers a useful model for research on marine fish, and as a result the
literature contains a great deal of Information relating to the rearing of this
species.
PART I - ECONOMICS
WORLD SUPPLY
When one is considering farming a marine species, it is important to look at the
supply of marine products provided by the fishing industry worldwide. Since the
market for fish is international,...the world supply is a good indicator of the
competition that products produced by aquaculture will face.
World catch
In recent years, the world catch of Atlantic cod has totalled about 1.9 million
tonnes, with five countries accounting for more than 60 per cent of the total.
In 1987, these countries were, in descending order, Canada, Iceland, Norway,
Denmark, and the United States. Of the 1 325 800 tonnes of cod landed by these
countries in 1987, Quebec accounted for 2.3% (Figure 1) (Lauzier, 1988).
Since 1983, cod landings by these countries have remained relatively stable
(Figure 2), which means that the supply of cod has not been the determining
factor in the price fluctuations in cod products in recent years.
Figure 1
Percentage distribution of cod catch among five main cod-fishing
nations in 1987 (figures for Canada exclude Quebec)
LEGEND (See original).
1. Canada
2. Iceland
3. Norway
4. United States
5. Denmark
6. Quebec
Figure 2 Cod catch in main cod-fishing nations, 1980 to 1988 (Figures for 1988
are projections.)
LEGEND (See original).
1.
2.
3.
4.
millions of metric tonnes
year
Denmark
United States
.
5. Norway
6. Iceland
7. Canada
The stability of the catch and the history of this fishery suggest that world
stocks are being fished at their maximum levels. Though the FAO thinks the
catch could be increased through a more effective management strategy, the world
supply of cod is unlikely to be increased significantly through traditional
fishing.
3
DEMAND
When supply is stable, demand influences the prices set in a free-market system.
It is therefore important to look at the demand situation when considering
.setting up a fish-farming operation. The economic viability of the project will
depend in part on the level of demand. In addition, by analyzing demand, we can
identify the most lucrative markets and determine their requirements as regards
raw materials.
The importance of the United States market to Quebec
In 1987, Quebec expcirted $32.2 million worth of cod products. Measured in dollar
value, 77 per cent of these exports went to the United States. Italy was the
next best customer, accounting for nearly 16 per cent of total value, followed
by Portugal, with 3.8 per cent, and the United Kingdom, with 2 per cent. The
remaining countries accounted for slightly over 1 per cent (Figure 3).
Figure 3
Exports of cod from Quebec in 1987, by country of destination
LEGEND (See original).
1. United States
2. United Kingdom
3. Italy
4. Portugal
5. Other countries
A more detailed analysis of Quebec's exports
of the American market varies from one cod
salted and dried cod products account for 41
of exports (Figure 4), and 50 per cent of
States.
Figure 4
shows that the relative importance
product to another. For example,
per cent of the total $32.2 million
these products went to the United
Exports of cod from Quebec in 1987, by product category
LEGEND (See original).
1. salted and dried
2. blocks
3. filets
4. other
Quebec's exports to Italy and Portugal also are concentrated in this product
category. As far as cod blocks are concerned, 96 per cent of Quebec's exports
go to the United States, and the same is true of cod filets. (In both of these
categories, the United Kingdom represents Quebec's second largest market.) It
can thus be readily seen why fluctuations in U.S. demand for Quebec's cod
products can have such a strong impact.
_
U.S. consumption trends
The United States represents a potential market of over 220 million consumers.
A slight change in per capita consumption can have substantial effects on the
4
fishing industry. For example; if annual per capita consumption of fish in the
United States increased by only 0.1 kilos, total demand would increase by 22 000
tonnes.
Consumption of seafood
Consumption of seafood in the United States has increased considerably since
1982, rising from 5.58 kg per capita in that year to 7.03 kg per capita in 1987
This represents an average increase of 5 per cent per year.
(Figure 5).
However, it is interesting to compare the actual pattern for recent years with
Analysts predicted that U.S. per capita
projections that were made in 1986.
consumption could reach 7.71 kg in 1987, if supplies were sufficient.
Figure 5
Consumption of sea food in the United states
LEGEND (See original).
2. year
1. actual
From 1986 on, it became obvious that the species traditionally consumed by the
American market could no longer meet the demand. As a result, prices of these
species increased significantly, and a search began for new species, such as
mahi—mahi and orange roughie, to meet this demand.
Unfortunately, this rapid increase in prices put ,
brake on consumption.
According to the most recent statistics, American cosumption of seafood is on
the decline. It dropped from 7 kg per capita in 1987 to 6.8 kg in 1988. The
most recent projections suggest that U.S. consumption of seafood products may
actually decrease slightly, or at best remain steady, for 1988.
Consumption of other sources of protein
To see how the increase in seafood prices has affected consumption, amaneedcmly
compare it with increases in the prices of the other major sources of protein.
U.S. price indexes show that from 1984 on, the price of fish has increased more
rapidly than that of other protein sources.
Figure 6
U.S. price indexes for four sources of protein, 1974-1987
LEGEND (See original.)
1. year
2. P = fish, b = beef, v = poultry, p = pork
This consumer resistance to an overly rapid price increase is all the more
striking in that Americans still consume far less fish than they do other sources
of protein (Figure 7).
5
Figure 7
U.S. consumption of four sources of protein, 1962 to 1988
LEGEND (See original.)
4. leef
5. year
1. fish
2. poultry
3. pork
It is interesting to compare the situation for fish with that for poultry, where
prices have increased more moderately, and consumption has been gradually
increasing.
The rapid increase in fish prices has caused resistance in consumers, resulting
in a slowdown and even a slight drop in the demand for fish. Now let us examine
the impact this drop in demand has had on the market for cod filets (representing
the market for both fresh and frozen cod) and on lightly salted dried cod
(representing the market for salted dried cod).
United States market for cod filets
Since the United States is the main market for cod filets from Canada, U.S.
demand can serve as an indicator of the prices Canadian companies might obtain
for commercially reareà cod products. Changes in inventories are one indicator
of this demand. Since fishing is a seasonal activity, wholesale distributors
must build up inventories during the fishing season, then work them down during
the off season. A change in demand will affect the cyclical rise and fall of
inventory levels. If demand increases unexpectedly, inventories will fall more
rapidly. If demand decreases, end-of-season inventories will be higher than in
preceding years.
U.S. inventories of cod filets
To meet demand in 1986 and 1987, American importers took a very aggressive stance
on world markets, dominating them by offering high prices and developing new
sources of supply. Then, in 1987, the slowdown in demand began to be felt.
American inventories of cod filets did not fall in the second half of that year,
whereas they normally do.
As a result of this situation, American inventories of cod filets have increased
almost continuously since the end of 1986. From a level of 7.4 million pounds
in November 1986, they rose to 36 million pounds in June 1988 (Figure 8).
Though such levels had already been reached in the past (1985, for example), at
those times demand was also on the rise.
Figure 8
End-of-month inventories of cod filets in the United States
LEGEND (See original.)
1. millions of kilograms
2. year
•■■[
6
U.S. imports
Volumes of imports are another indicator of market demand. Strong demand will
cause buyers to intervene aggressively in international markets to ensure an
adequate supply.
As a result, the annual volume of imports will increase.
Conversely, if demand decreases, so will imports.
The impact of the rise in inventories caused by the fall in American consumption
of bottom fish is being felt by all the countries from which the United States.
imports (Figure 9). However, Canada, which accounted for 60 per cent of U.S.
Imports as of 30 June 1987, accounted for 63.7 per cent exactly one year later.
The loss of market share was felt - by Denmark and Norway, whose exports to the
U.S. dropped by 55 and 27 per cent, respectively. Exchange rates have definitely
played a role here, and these countries will probably be directing a greater
portion of their production to Europe, where exchange rates are more favourable
for them.
Figure 9 U.S. imports of cod filets, by country of origin, for the first six
months of 1986, 1987, and 1988
LEGEND (See original.)
1.
2.
3.
4.
thousands of metric tonnes
year
other countries
Iceland
5. Norway
6. Denmark
7. Canada
Current conditions in the U.S. market for cod can be summarized as follows:
stabilization of supply and a drop in demand. What effect do these conditions
have on prices?
Prices
In assessing the economic feasibility of a fiah—farming project, the changes over
time in the prices that the fishing industry has received for its catch can give
some indication of the prices that fish farmers might receive for their harvest.
The trend will indicate whether fish farmers can expect prices to rise or fall
in future.
As U.S. inventories of cod filets began to rise toward the end of 1986, prices
for the various types of frozen cod filets began to drop and/or stabilize. The
price for Canadian . filets peaked in January 1987, then dropped gradually,
reaching SUS 1.75 per pound in October 1988. It is expected to stabilize at
about $US 2.00 per pound.
The exchange rate is another factor that has affected the price of cod (Figure
10). The U.S. dollar has fallen relative to the Canadian, forcing Canadian
processors in general to absorb up to 8 per cent of the decrease in the price
of filets. The appreciation of the Canadian currency has not caused the drop
in prices on the American market, but has rather accentuated this trend.
7
Figure 10
Effect of exchange rates on the monthly price for cod filets
(Canada/5 11,s/1-2). Prices are shown at the January 1986 exchange rate
(c) and current exchange rates (v).
'LEGEND (See original.)
1. Canadian dollars/pound (v = current exchange rates, c = January 1986 exchange
rate)
Over this same period, prices for Norwegian and Icelandic filets managed to
maintain the levels they had reached at the end of 1986. The quality of the
European product explains part of the price difference.
mus the money markets have a definite influence on the market for fish.
Exchange rates are a very important factor for a country such as Iceland, with
its fishing-based economy (Figure 11). To counter the rise in its currency
relative to the U.S. dollar and keeps its products competitive on international
markets, Iceland devalued its currency voluntarily.
Figure 11
Effect of exchange rates on the monthly price for cod filets
(Iceland/5 11,s/1-2). Prices are shown at the January 1986 exchange
rate (c) and current exchange rates (v).
LEGEND (See original.)
1. Icelandic krona (v = current exchange rates, c = January 1986 exchange rate)
Worldwide, the market for fresh and frozen cod is on the decline. This trend
could give way te somesteadying-of prices once inventories have returned to
normal levels.
Now let us examine the market for salted dried cod, the second largest market
for cod from Quebec.
Market for salted dried cod
Of all the salted dried cod products produced in Quebec, lightly salted cod is
the main export product. In 1987, the main markets for this type of cod were
the United States and Italy (Figure 12). The United States took 53.7 per cent
of Quebec's exports of lightly salted cod, mainly lightly salted cod with over
43 per cent moisture content. Italy took 44.3 per cent, mainly lightly salted
cod with a moisture content of 43 per cent or less.
't
8
Figure 12 Quebec exports of lightly salted cod, by country of dest4rnation,1987
T.
LEGEND (See original.)
1. Italy
2. United States
3. Other countries
Since 1985, there has been a significant change in the export markets for salted
dried cod. The value of Quebec's exports of this product to - Italy has increased
continuously, while the value of its exports of this product'to the United States
has declined (Figure 13).
Figure 13 Quebec exports of lightly salted cod, by country:« destination,'1985
,
to 1987
LEGEND (See original.)
1. millions of Canadian dollars
2. year
3. United Stated:,
4. Italy
Prices for exports of lightly salted cod have risen faster in Italy than in the
United States (Figure 14). Italian demand for this product seems to be holding
steady, since prices in 1988 maintained their 1987 leVels, contrary to the
general downward trend on all other markets for Canadian cod.
Figure 14 Prices for lightly salted cod, Italy and the United States, 1985 to
1988
LEGEND (See original.)
1. Canadian dollars per pound
2. year
3. Italy
4. United States
In addition, the exchange rate between the Italian lira and the Canadian dollar
remains favourable to Canadian exports.
TEE POTENTIAL FOR COD FARMING IN QUEBEC
,
Certain Indicators of the situation for cod in Quebec suggest that there may be
a market for commercially reared cod.
Landings of cod have been on the decline in Quebec since 1985 (Figure 15).
Preliminary figures for the 1988 season indicate that the catch will be even
smaller than in 1987. For the Gulf of St Lawrence as a whole, fishing operations
using fixed gear are suffering the most.
9
Figure 15 Landings of cod in Quebec, 1984 to 1988
LEGEND (See original.)
1. thousands of metric tonnes
2. year
This means that large cod are even scarcer on markets, because a high proportion
of large cod are taken with fixed gear, mainly longlines. All this means that
processors are finding it increasingly difficult to secure a sufficient supply
of cod to keep their operations going throughout the season.
The supply of salted dried cod on the market is limited by the availability of
the large-sized cod needed to make this product. In 1988, large cod were scarce
enough that they commanded a higher price.
In Quebec, as throughout the Gulf, it was the vessels using fixed gear
(longliners) that captured the largest cod. Large longliners (50 feet and over)
can range farther than smaller ones and therefore have a better chance of going
where large cod can be found. In 1988, the dockside prices for cod taken by
longliners in the Gulf directly reflected size differences in these vessels ad
in their catch (Figure 16). Thus cod farmers might find it to their advantage
It remains to be seen,
to raise larger cod which commanded higher prices.
however, whether these price differences observed in 1988 will recur in future.
Figure 16 Dockside prices for cod taken by three size classes of longliner in
Quebec, 1984 to 1988
LEGEND (See original.)
1. Canadian dollars per pound
2. year
3. 1988 figures are preliminary.
The price of cod filets on the Boston market seems to show some slight seasonal
variation, with prices being 5 per cent higher out of season (Figure 17). Cod
farmers might therefore be able to get better prices by selling their product
out of season (that is, in December and January). On the other hand, if we look
at the average dockside prices for each calendar month for Quebec cod and for
cod taken by longliners in the Nova Scotia-Bay of Fundy region, no particular
seasonal pattern emerges.
This
Icelandic and Norwegian cod fetches higher prices than cod from Quebec.
price difference is often attributed to the higher quality that buyers perceive
the Scandinavian products as having. A cod farming operation might be able to
improve product quality and thus obtain prices equal to or even higher than
those paid for Icelandic cod.
•
•
10
Figure 17 Seasonal variations in the price of frozen cod filets on the Boston
market (average price for each calendar month, 1983 to 1988)
LEGEND (See original.)
1. Jan, Feb, ... , Dec
Microeconomic considerations
Little information is currently available on existing cod-farming operations.
Cod farming is carried on in Norway, where juveiilles are raised on a large scale
in wide, enclosed bays. The fish reach a weight of 2 kilos in about two years.
But the commercial viability of these operations has yet to be demonstrated.
A Scottish-Norwegian joint venture is in the process of planning to rear cod in
floating cages in northeastern Scotland. The Norwegians are supposed to provide
5 to 10 thousand fry to start up operations in 1988 to 1989. There is also a
private fish-farming facility in Newfoundland that specializes in on-growing
small trap cod which have little initial value.
There is now enough knowledge about rearing saltwater fish in floating cages to
make some realistic assumptions about the costs of rearing saltwater fish in
general (Table 1).
According to Myrseth (1988), saltwater fish with a market price greater than or
equal to $CAN 5.70 per kilogram could be farmed profitably in Europe. In New
Brunswick, the cost of rearing salmon in cages has been estimated at $7.24/kg
(Fiander and Good, 1988). At present, cod is considered a low-value fish, and
its market price is still well below $5.70/kg. On the other hand, some species,
such as trout and catfish, have much lower production costs than those just
mentioned. Cod may have a production-cost structure similar to that of these
species, but this remains to be shown.
The information available on this subject comes from a study by Jones' (1984).
Jones developed a financial model of a commercial operation that raises cod from
eggs to commercial size. His conclusions were as follows: "Technically, cod
farming is possible, but economic projections indicate a production cost greater
than the market price. Under current conditions, this type of farming cannot
be profitable. A small operation with access to low-cost feed and to a
specialized market could be profitable." [retranslated from the French - tr]
But would it be profitable to farm cod in Quebec? This is the question that
Cantin and Bourdages attempt to answer in their 1989 study.
11
Table 1
Estimated costs of producing saltwater fish in floating cages in Europe
and Atlantic salmon in Canada
LEGEND (See original.)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
estimated cost
saltwater fish, Europe
Atlantic salmon, Canada
investment
food conversion ratio
cost of feed .
production per employee per year
interest
depreciation period
production costs ($/kg)
feed
fry
13. labour
14. other operating costs
15. service/maintenance
16. administration
17. depreciation
18. interest on investment
19. interest on credit margin
20. total production costs
21. metric tonnes
22. years
23. * excepting motors and vehicles
12
PART II - COD BIbLOGY AND COD-REARING EXPERIMENTS
REPRODUCTION
The reproductive cycle of fish is important to fish-farming operations for two
reasons. First, on-growing facilities must be familiar with the factors
triggering sexual maturation, which slows growth and hence Increases production
costs. Second, farmers who wish to maintain brood stocks must control the sexual
maturation cycle so as to obtain gametes from both sexes simultaneously and, if
possible, throughout the year.
Sexual maturation
Cod have a very long spawning season. Between Newfoundland and the Georges Bank,
In the
it lasts from January to June (Fahay, 1983; Scott and Scott, 1988).
southern part of the Gulf of St Lawrence, it begins in May, peaks at the end of
June, and ends in the fall (Fowles, 1958). However, the size of the eggs, and
hence their viability, decreases as the season goes on (Sars, cited in Knutsen
and Tilseth, 1985).
The minimum size at sexual maturation varies from one stock to another, but is
generally around 30 to 35 cm. Median size is about 40 cm, and all cod over 50
cm long are sexually mature (Beacham, 1983 a and b; Baird et al, 1986). Holdway
and Beamish (1985) and Walsh et al (1986) have identified histological criteria
that can be used to distinguish immature cod from spawners, several months in
advance. Unfortunately, cod have no visible secondary sexual characteristics,
except perhaps for the formation of breeding tubercles in the males (Vladykov
et al, 1985). Cod that are in the process of sexual maturation stop feeding,
in captivity at least. For two months, their growth is negative, resulting in
a weight loss associated with spawning amounting to 16 per cent in males and 27
per cent in females (Braaten, 1984).
Fecundity is high. It can be calculated with the following formula:
F = 0.50 L3 . 42
(May, 1967)
where L is the length in centimetres and F is fecundity in millions of eggs.
According to this formula, a cod 40 cm long produces 150 000 eggs and a cod 80 cm
long about 1 600 000 eggs. Even though fecundity is a function of weight, the
number of eggs per unit weight is constant (Eliassen and Vahl, 1982).
Fertilization methods
Techniques for fertilizing eggs in vitro after collecting gametes from one male
and one female or from several males and several females are the same as for
other fish. Gametes can be stored in air at temperatures of 5°C for several
hours (Kjorsvik and Lonning, 1983), but eggs kept in sea water quickly become
sterile (Figure 18; Davenport et al, 1981).
Both the dry method and the wet
method have given good results. The dry method consists in fertilizing the eggs
in a container that does not contain any sea water, though it must be wetted down
13
in advance. In the wet method, the eggs are placed in sea water, generally at
5 or 6 ° C (the temperature at which spawning takes place), and the milt is then
added. The mixture is allowed to rest for a period ranging from several minutes
to one hour, and is then rinsed with sea water several times (Shelbourne, 1964;
Kjorsvik and Lonning, 1983; Iversen and Danielssen, 1984).
Figure 18
Fertility of eggs as a function of time kept in sea water (from
Davenport et al, 1981)
LEGEND (See original.)
1.
2.
percentage of eggs successfully fertilized
time in hours
Some authors prefer the technique of "natural" fertilization in a tank or pond
(Laurence and Rogers, 1976; Jones, 1984). This technique is scarcely new, as
it was used very early on in Norway (Solemdal et al, 1984). In this method the
eggs, fertilized without human intervention, are gathered by straining the water
with a fine-mesh net, usually at the surface (Laurence and Rogers, 1976; Howell,
1984). The buoyancy of the eggs depends on many factors; these will be discussed
later in this paper. A few weeks before spawning, the cod become aggressive
toward each other, with one vigourous male becoming dominant and establishing
a territory that the non-dominant individuals stay out of. All spawning takes
place within this dominant male's territory, generally close to the surface and
at night (Brawn, 1961 a and b). The females do not deposit all their eggs at
the same time, but rather over a period of 2 to 3 weeks (Shelbourne, 1964;
Holdway and Beamish, 1985). The eggs released last are smaller and less viable
than those released first (Knutsen and Tilseth, 1985). According to Shelbourne,
eggs produced by this natural method are of better quality.
EMBRYO DEVELOPMENT
Cod eggs are pelagic. They have a diameter of 1.2 to 1.6 trim when placed in
contact with water. The chorion is transparent, so that one can observe the yolk
inside. This yolk is homogenous and contains no oil globules. The buoyancy of
cod eggs is attributable to their high water content, 92 per cent (Craik and
Harvey, 1987). Several authors have described methods of incubating floating
eggs (Shelbourne, 1964; Thompson and Riley, 1981; Howell, 1984; Kjorsvik and
Lonning, 1983; Solberg and Tilseth ., 1984).
The stages of embryo development have been defined and described by many authors,
including Laurence and Rogers (1976), Thompson and Riley (1981), Fahay (1983),
and Makhotin et al (1984). The length of the incubation period is directly
proportional to temperature (Figure 19) . , and this relationship may be described
as follows:
Y = 21.96 - 1.30 X
(Laurence and Rogers, 1976)
1
1
tà
4
14
where Y is the time in days and X is the temperature in degrees Celsius.
Figure 19
Length of incubation period as a function of temperature, for larval
stages 1A, 1B, 2, 3, 4, and 5 (adapted from Thompson and Riley, 1984)
LEGEND (See original.)
1.
days
2.
temperature (degrees Celsius)
Similar results have been obtained by authors such as Thompson and Riley (1981;
10 days at 12 °C, 17 days at 6.5 °C, and 28 days at 1.7 °C) and Kuftina and Novikov
(1986; 16 days at 6°C and 43 days-at 0 °C).
Cod embryos develop normally between —1.5 and 100C (Makhotin et al, 1984), but
this may vary from one stock to another: Thompson and Riley (1981) found that
in more southerly stocks, no eggs hatched at temperatures below 1.5 °C. At sea,
cod eggs are concentrated at temperatures of 5°C (Ellertsen et al, 1984).
Another finding is that energy reserves are converted at a lower rate at 0°C than
at 6°C (Kuftina and Novikov, 1986). On the other hand, Makhotin et al (1984)
report that embryos are larger and better developed when hatched at 1°Fthan at
But warmer temperatures can also pose
6 °C (4.9 mm compared with 4.2 mm).
studied
by
Thompson
problems. For the stock
and Riley (1981), hatch rates were
12°C.
at
temperatures
above
Iversen and Danielsen (1984) managed to obtain
zero
but
embryo development was slower, and the rates
larvae at these temperatures,
deformities
increased.
of mortality and
In a study by Solberg and Tilseth (1984), some 95 per cent of embryos incubated
under light hatched at each of three temperatures (3, 5, and 7°C). For embryos
incubated in darkness, the percentage remained the same at 7°C, but dropped to
85 per cent at 5°C and 75 per cent at 3°C.
Successful fertilization decreases at salinity levels below 34 g/L, and at
14 g/L, it reaches zero (Kjorsvik et al, 1984). Laurence and Rogers (1976) found
the mortality rate for embryos was higher at 26 g/I, than at 36 g/L, but the
length of the incubation period did not vary. Davenport et al (1981) describe
embryo development as normal at salinity levels as low as 10 g/L, but abnormal
at 7 g/L.
LARVAE
The larval period runs from the time the eggs hatch to the time metamorphosis
The
occurs. It is generally during this period that mortality is highest.
stages in the development of cod larvae have been described by Thompson and Riley
(1981) and Makhotin et al (1984). When first hatched, the larvae measure about
4.5 mm and weigh about 200 micrograms (Olafsen, 1984). They can begin to feed
after one day (Laurence, 1978), but more generally do so after four or five
•
t.
15
.
.
(Gamble and Roude, 1984). In the meantime, they meet their nutritional needs
from their yolk sac, until the eyes, mouth, and intestines have become functional
(Yin and Blaxter, 1987a). The yolk sac is completely resorbed about the seventh
day after the egg has hatched, and it is at this time that feeding activity
reaches its peak. Between the fifth and the eleventh day, the larvae must begin
to draw their nutrition solely from the outside world. At ambient temperatures
of 7 °C, if they have not met their energy requirements at the end of the eleventh
day, they will die within the five days that follow (Yin and Blaxter, 1987a).
When cod are being reared artificially, the size of the prey is a critical
factor, especially in the first few days following hatching. When the larvae
begin to feed, theY cannot ingest the nauplii of Artemia spp., a zooplankton
commonly used to feed cod larvae. Furthermore, a diet composed solely of
rotifers or of Artémia nauplii does not meet all nutritional requirements and
will not allow the larvae to survive until metamorphosis (Rowell, 1984). Rowell
suggests feeding the larvae rotifers at first, then switching over to Artemia
metanauplii, preferably fed on a mixture of two algae. At present, no artificial
feed is available for cod larvae of this size (Helmeland et al, 1984; Oiestad
et al, 1985). The techniques for producing algae, rotif ers, and Artemia spp.,
as well as the densities of these organisms and other zooplankton provided to
the larvae, have been described by various authors, including Thompson and Riley
(1981), Rowell (1973, 1984), Solberg and Tilseth (1984), and Tilseth and
Ellertsen (1984).
Little information is available on the factors influencing the capture of prey
by the cod larvae. These larvae are visual predators. They feed sporadically,
and they require an illumination on the order of 0.1 lux to detect their prey
(Ellertsen et al, 1984; Tilseth and Ellertsen, 1984). In nature, they stay near
the surface, feeding on the nauplii of copepods. The size of this prey depends
on the size,of the larvae themselves: the smaller larvae feed on the smaller
crustaceans (Lough, 1984). Gradually, they stop feeding on nauplii and turn to
more advanced stages of calanoid copepods, until metamorphosis (Rvenseth and
Oiestad, 1984.) In the laboratory, when given a choice, cod larvae prefer
They
copepod nauplii (Ellertsen et al, 1984; Tilseth and Ellertsen, 1984).
consume one nauplius per hour, up to a maximum of three or four nauplii. The
time it takes to digest one nauplius is 30 minutes, at 5°C (Tilseth and
Ellertsen, 1984). There are many methods of detecting nutritional problems in
cod larvae. Visual methods are discussed in Oiestad (1984), Tilseth and
Ellertsen (1984), and Yin and Blaxter (1986). Biochemical methods are discussed
in Buckley (1979, 1981, 1984) and Raae et al (1988).
Mortality
In a series of experiments reported in 1984, Rowell found that 10 per cent of
cod larvae survived until metamorphosis and that 5 to 7 per cent survived for
72 days, attaining a final size of 3.5 cm. Mortality factors include inadequate
diet and cannibalism. Rowell observed a'bimodal length distribution on the 30th
day of life (Figure 20), due to a lag in the growth of those larvae that had not
succeeded in filling their swim bladders. Once the critical period has passed,
the mortality rate remains constant (Raae et al, 1988). In Norway, when cod
f
16
larvae were transferred into enclosed ponds at the age of 5 days, the survival
rate until metamorphosis was 2 per cent in the first two years. Subsequently,
steps were taken to prevent jellyfish from preying on the larvae, and this rate
increased to 30 and even 50 per cent (Rvenseth and Oiestad, 1984; Oiestad et al,
1985).
Figure 20
Length distribution of cod larvae with and without swim bladders after
30 days (from Howell, 1984). Black bars on left represent larvae
without bladders; grey bars on right represent larvae with bladders.
LEGEND (See original.)
1.
percentage frequency
2.
length (mm)
The lethal temperature and salinity for starving larvae (LC50 , 24 h) are,
respectively, 16 to 18°C (at 32 g/L) and 2 to 3 g/L (at 6°C) (Yin and Blaxter,
1987b).
Growth
Laurence (1978) reports that metamorphosis occurs when the larvae have reached
a length of 10 mm and a dry weight of 1 000 micrograms, after 44 days aè 10 0C
or 52 days at 7°C. Rvenseth and Oiestad (1984) and Oiestad et al (1985) give
figures of 12 imn and 1 800 micrograms after 35 to 40 days. —"Yin and Blaxter
(1986) find that from hatching to the 32nd day of life, larvae kept at 7°C grow
0.083 mm per day. These authors give the following equation:
length = 4.502 + (0.083 x age in days)
Buckley (1981) cites a growth rate of 1.8% per day between the 23rd and the 62nd
day following hatching. Buckley gives the equation:
length = 1.50 + (0.018 x age in days)
Curves showing growth in mass of larvae up to the time of metamorphosis can be
found in Kvenseth and Oiestad (1984) and Laurence (1978, 1979).
JUVENILES AND ADULTS
Distribution
Cod can be found at depths of 30 to 400 m, temperatures of 0 to 13 °C, and
salinities of 31 to 34 g/L, but they generally frequent depths of 40 to 100 m,
at temperatures of 3 to 4°C for northern stocks and 7 to 8°C for southern ones
(Scott, 1982). In the Gulf of St Lawrence, the vertical distribution of cod
varies with size; cod less than 20 cm long stay closer to shore, in the
intermediate layer (Jean, 1964). This is also the case in the eastern Atlantic
(Figure 21), where the juveniles remain in shallower water and individuals under
one year old even swim up estuaries to waters where salinity is only 10 to 20 g/L
and no older cod are present (Riley and Parnell, 1984). Cod less than 20 cm long
do not seem to migrate outside the Gulf of St Lawrence in winter, but the larger
cod make seasonal migrations, seeking deeper water in the Atlantic. They return
to shallower water closer to shore around mid—June (Jean, 1964).
17
Figure 21
Distribution of cod less than one year old as a function of salinity
along the coasts of England in September and October, 1970 to 1975
(from Riley and Parnell, 1984)
LEGEND (See original.)
1. index of relative abundance (normalized average percentage)
2. salinity (g/L)
Diet
Like cod larvae, juvenile and adult cod are visual predators. They can find and
pick up particles as small as 2 mm in size. The changeover to scotopic vision
takes place at illuminations on the order of 10_2 to 10_a lux (Ali, 1971). Cod
can also use the taste buds in the barbel and the pelvic fins to detect food
buried in the substrate and fine particles lying on the bottom (Brawn, 1969).
The amino acids glycine and alanine seem to be good triggers for the feeding
process (Ellingsen and Doving, 1986). Once cod reach lengths of 2.5 to 3.0 cm,
they will readily eat feed pellets, and from this size on survival rates are the
same regardless of whether the diet consists of pellets or of Artemia spp.
(Bormley and Sykes, 1985). Cod taken in the wild and brought to our facilities
began to eat pellets or fish only a few days after their arrival.
In their natural environment, cod feed on several species of crustaceans or fish.
Unfortunately, the incidence of cannibalism is not negligible, and could be
significant in farming operations, because non—domesticated stocks are,
characterized by large individual variations in growth rates. In nature, the
incidence of cannibalism increases with size. It is absent in cod less than 50
cm long, but increases gradually as the fish grow larger, representing up to 7
per cent of the diet of cod over 81 cm long (Waiwood and Majkowski, 1984). In
the stomachs of cod from the Saguenay River, 10 per cent of the fish are cod
(Lalancette, 1984). Cod between 10 and 25 cm long seem to be the main victims
of this cannibalism (Templeman, 1976), which could explain why cod are segregated
by size in the natural environment (Jean, 1964 and Riley and Parnell, 1984).
In farming operations, cannibalism can occur at any size. Bromley and Sykes
(1985) found that several cases of mortality were due to cannibalism in cod 2.5
to 3.0 cm long. Though cannibalism generally takes place between individuals
of different sizes, attacks can also occur between individuals of the same size
(Brawn, 1961a; Bromley and Sykes, 1985). Aggressiveness between cod of the same
size is associated with the establishment of a hierarchy between these
individuals. In extreme cases, cod at the bottom of the hierarchy, having been
threatened and bitten repeatedly, may even die as the result of their injuries
or of forced starvation. This behaviour has been observed in small groups of
cod in three length classes between 5 and 90 cm (Brawn, 1961a). Cannibalism
occurs more frequently when cod receive a smaller ration (Oiestad et al, 1985).
When the ration is held constant, cannibalism may increase with temperature; as
the present authors observed in our tanks last spring. Very likely such
interactions have less chance of occurring in tanks with very high densities.
4
ç.
18
Metabolism
Metabolism in fish depends on several factors, in particular their weight and
the temperature of their environment. Metabolism is usually measured by oxygen
consumption, because the factors influencing metabolism influence oxygen
consumption as well. Assuming a temperature of 8.4°C, Braaten (1984) gives the
following equation expressing a fish's oxygen consumption in milligrams of oxygen
per hour (Q02 ) as a function of its weight in grams (W):
Q02 = 0.0204 e' 824
For a temperature of 12 °C, Saunders (1963) gives this equation:
Q02 = 0.245 Wee ' 82
Thus cod weighing 500 g consume about 25 mg of oxygen per hour at 3 °C and 46 mg
of oxygen per hour at 15°C, while cod weighing 6 kg consume 178 mg and 354 mg
The increase in oxygen
at these same two temperatures (Saunders, 1963).
consumption after feeding is very pronounced in cod and depends on the ration,
the number of meals, and the temperature (Figure 22). Oxygen consumption drops
back to the baseline level 24 hours after the meal, or several days later if the
cod has eaten several meals over a short period (Soofiani and Hawkins, 1982).
These factors are decisive, because cod cannot tolerate oxygen concentrations
below 3 mg/L at 100C (Saunders, 1963).
Figure 22
Increase in oxygen consumption over time for a cod fed to satiety.
Points represent average consumption over 24 hours. Meals are marked
on the x axis. (from Soofiani and Hawkins, 1982)
LEGEND (See original.)
1.
2.
oxygen consumption (milligrams per kilogram-hour)
days
Temperature will also affect the quantity of food ingested, the proportion of
the energy consumed that will be needed to meet the organism's basic needs, and
the proportion of this energy that will be used for growth. The composition of
the fish's diet will likewise affect consumption and growth. Since feed
represents a large percentage of the operating costs of a fish farm, these
variables may determine the success or failure, or at least the profit margin,
of such an operation. In the following pages we examine only the information
related specifically to cod, since the general principles regarding the
metabolism of cold-blooded animals are valid for cod as well.
•
•
19
Base ration
The terni base ration is defined here as the ration that an organism must receive
to keep its weight constant. Base ration is a function of weight, as shown in
the following equations:
[Translator's note: The superscripts in these equations were not clear in the
photocopy submitted for translation and should be checked before this translation
goes to press.]
(Jones and Hislop, 1978)
At 13°C
= 0.023 WM°
At 10°C
RB = 0 017 W055
(Jobling, 1982)
B = 0 025 e' 77R
(Braaten, 1984)
At 8°C
.
.
where RB is the base ration in kilocalories per day and W is the weight in grams.
The relationship between the base ration for a fish and its weight is affected
by temperature, because the base ration increases exponentially with temperature.
For example, for cod measuring less than 40 cm, Hawkins et al (1985) give the
following equation for the 7 to 18°C temperature range:
Log R B = 0.065 T - 1.018
where RB is the base ration expressed as a percentage of weight and T is the
temperature in degrees Celsius. Thus the daily base ration for a cod would be
0.4% of body weight at 10°C, compared with 0.9% at 15°C (Hawkins et al, 1985).
Curiously, however, Jobling (1982) did not find any relation between base ration
and temperature. Kohler (1964) says that individual cod weighing 510 g and 750
g, when kept at ambient temperatures ranging from 2.5 to 15°C, require 1176 g
and 1375 g of herring per year, respectively, to keep their weight constant.
Ingestion and digestion
The amount of food that a cod ingests during a meal increases with its body
weight (Jobling, 1983) and decreases with temperature. But it should be noted
that cod continue to eat food when offered at temperatures as low as 0 or 1°C
(Saunders, 1963; unpublished data from the authors' experimental rearing
facilities). In an on-growing experiment, Williams and Kiceniuk (1986) observed
an average consumption of 190 g/kg/week in cod 40 to 60 cm long that'were fed
to satiety three times per week at temperatures ranging from 7 to 15 °C. Food
consumption is 1.5 times greater when the cod are fed to satiety two times per
day instead of one time at 4.5°C (Braaten and Gokstad, 1980), which likely
reflects the rate at which the food is evacuated from the stomach to the
intestine (Tyler, 1970). This rate varies with temperature (Figure 23): at 5°C,
the stomach becomes empty in 2.5 days, but at 10°C, it does so within 24.hours.
The rate seems to peak at 15 °C then decrease at higher temperatures, which would
indicate that the optimal temperature for growth is around 15 °C (Tyler, 1970).
Using this information, one can calculate the number of meals to provide each
week and the ration to give each cod to provide it with a maximum amount of
energy in accordance with its size and the temperature of its environment.
à
•
•
20
Figure 23
Decrease in weight of food in stomach as a function of number of hours
since last meal, at 2°C and 10°C (from Tyler, 1970)
LEGEND (See original.)
1. amount recovered, in grams
2. hours
FoOd conversion ratios
The gross food conversion ratio Is the ratio between the amount of food ingested
and the amount of growth. The net food conversion ratio is the ratio between
the amount of food assimilated and the amount of growth. Such ratios are useful
because they indicate what yield is being obtained from the fishes' diets.
Conversion ratios must therefore be taken into account when calculating
production costs. For cod, only gross conversion ratios have been estimated.
Caution must be exercised in comparing conversion ratios, because they can be
calculated on various bases, such as wet weight, dry weight, and energy content,
and including or excluding the base maintenance ration.
Above and beyond the maintenance ration, the conversion ratio (calculated as the
slope of the equation relating growth in kilocalories per day to food consumed
in kilocalories per day) reaches a peak of 24 per cent when an intermediate
amount of rations was are fed to cod weighing 100 to 900 g, at temperatures of
15°C (Edwards et al, 1972). This is because the energy cost of assimilation is
not constant, but rather increases with the temperature and with the size of the
ration. It is highest (20 per cent of the energy ingested) at 18 °C with maximum
rations, that is, when the fish are fed to satiety, and varies from 3 to 20 per
cent depending on conditions (Soofiani and Hawkins, 1982).
The conversion ratio decreases with the size of the fish according to the
equation:
G 079 w-0.15
or
CG
u-0.18
La n
n
v.uJ
(Jones and Hislop, 1978)
(Jobling, 1982)
[Translator's note: The superscripts and subscripts in these equations were not
clear in the photocopy submitted for translation and should be checked before
it goes to press.]
where C B is the gross conversion ratio (calculated as the slope of the equation
relating growth in kilocalories per day to food consumed in kilocalories per day)
and W is the weight in grams for fishes weighing less than 900 grams.
The conversion ratio also varies with diet. In an experiment reported by Howell
(1984), cod initially measuring 3.5 cm were fed exclusively on pellets for 4
months, at the end of which they measured 12 cm. Subsequently, one group of
these cod continued to receive pellets while the other were fed Ammodytes spp.,
twice per day to satiety. The cod fed on pellets grew more slowly than those
fed on Ammodytes (2.34 cm per month versus 2.73 cm per month) at ambient
temperatures• Kohler (1964) reports that beyond the maintenance ration, cod that
measured 34 to 54 cm and were fed to satiety on herring converted 2.2 kg of food
into 1 kg of body weight at temperatures ranging from 2.5 to 15 °C. In Howell
21
(1984), cod measuring 24 to 34 cm that were fed various species of fish required
2.3 kg of food for every kilogram of growth at temperatures of 6 to 18°C.
Williams and Kiceniuk measured lower conversion ratios in cod 40 to 60 cm long
• that were fed to satiety on capelin three times per week at temperatures of 7
to 15°C.
Growth
Cod grow rapidly. Braaten (1984) was able to produce cod weighing 4 kg within
2.5 years of fertilization. Working in saltwater ponds, Oiestad et al (1985)
raised cod from metamorphosed larvae to a length of 18 cm and a weight of 60 g
in less than 6 months. Howell (1984) produced cod measuring 12 cm (18 g) after
18 weeks and 34 cm (475 g) after 60 weeks. Williams and Kiceniuk (1986) obtained
average weight increases of 66 per cent and 79 per cent in 12 and 14 weeks,
respectively, in two trials where cod 40 to 60 cm long were fed to satiety 3
times per week.at temperatures of 7 to 15°C.
Cod grow fastest at temperatures of 13 to 15 °C, according to Jobling (1983).
Tyler's 1970 study, based on the rate of emptying of cods' stomachs, suggests
the same finding. These are the same temperatures that cod select when placed
in a temperature gradient (Bohle, 1974), but not the same temperatures at which
Howell (1984) suggests
cod are found in nature (Jean, 1964; Scott, 1982).
temperatures of 10 to 13°C instead.
According to Hawkins et al (1985), the specific growth rate is a function of the
ration at all temperatures, and, when the ration is held constant, growth is
fastest at low temperatures, because the base maintenance ration increases with
temperature.
On the other hand, even if the conversion ratio decreases as
temperature increases, food consumption also increases, and cod fed to satiety
grow fastest at higher temperatures (Hawkins et al,. 1985). The following
equations express the relationship between the specific growth rate Gs and the
food ration R, with both variables measured in percentage of fresh weight per
et al (1985); the last is from
day. The first two equations are from Hawkins Houlihan et al (1988).
100 g fish at 10°C
Gs = -0.0520 + 0.1894 R s
400 g fish at 10°C
Gs = -0.1939 + 0.2428 Rs
300 g fishes kept at 10 °C
for 3 months
Gs = -0.58 + 1.13 Rs
Braaten (1984) gives the equation:
Log G = -1.16 + 0.52 Log R
where . G is growth in kilocalories per day and R is the food ration in
kilocalories per day for fish weighing 200 to 300 g and kept at 8.4°C. This
relationship between growth and ration has also been demonstrated for cod
weighing less than 900 g (Edwards et al, 1972; Jones and Hislop, 1978).
Many species of fish store energy consumed in excets of basic metabolic
•
22
requirements along their intestines and under the skin in the form of fat. But
cod channel this energy into growing additional liver and muscle tissue (Edwards
et al, 1972). Hence the ratio of liver weight to total weight increases linearly
with the food ration. Holdway and Beamish (1984) report that the weight of the
liver varies seasonally, reflecting variations in the fat content and the growth
rate of the cod. These authors provide curves that can be used to determine the
fat, protein, water, and energy content of cod from measurements for only one
of these variables.
The following equations show how the growth rate of cod decreases with their
size. The first equation is from Jobling (1983), the second from Braaten (1984).
In these equations, G is the specific growth arid W the weight in grams.
Cod weighing 100 to 1000 g,
kept at 10 to 14°C
Log?G = 2.93 - 0.441 Log? W
Cod weighing 4 kg or less,
kept at 6 to 9 °C
G . 9.68 w-0.45
[Translator's note: The superscripts and subscripts in these equations were not
clear in the photocopy submitted for translation and should be checked before
it goes to press.]
In this way Braaten (1984) determined that the specific rate of growth in weight
for cod was 1.4 to 2.0% per day between 3.6 and 90 g, 0.8 to 1.7% per day between
90 and 800 g, and 0.2 to 0.3% per day at higher weights (Figure 24). Howell
(1984) measured a growth rate of 27 mm per month for cod less than 12 cm long
and 19 mm per month for cod 12 to 34 cm long, kept at temperatures ranging from
6 to 16°C. In Kohler (1964), cod measuring 34 cm (450 g) and 42 cm (760 g) were
fed to satiety for one year at temperatures ranging from 2.5 to 15°C. The smaller
cod grew 15 cm in length and 157% in weight, while the larger cod grew only 11 cm
in length and 98% in weight.
Figure 24
Rate of growth in weight as a function of the [initial?] weight of
cod fed to satiety at 8.5°C (Braaten, 1984)
LEGEND (See original.)
1. growth rate (% of weight per day)
2.
weight in grams
Diseases
The crowded conditions arising from high densities in fish-farming facilities
make it important to have a good knowledge of methods of preventing and treating
bacterial, viral, and fungal diseases. Unfortunately, methods developed to treat
bacterial diseases in salmonids, for example, may prove totally ineffective for
marine fish. Nevertheless, anyone planning to rear fish should have a good
knowledge of their most common diseases. Little has been published about the
diseases to which cod are subject in nature or in captivity, probably because
little research has been done on this subject. Only two diseases have been
reported to date. The most harmful is vibriosis, caused by the bacterium
Vibrio anquillarum. The most common symptoms of this disease are skin lesions,
boils, and hemorrhages, erosion of the tail fin, and exophthalmia. Several
23
stocks of cod seem to be affected by this disease [several strains of this
bacterium seem to be responsible for this disease? —tr], and the treatments
tested to date have been unsuccessful, though the Norwegians are in the process
of developing a vaccine (Egidius and Andersen, 1984). The other disease reported
in the literature is viral erythrocytic necrosis (VEN), caused by a virus of the
family Iridoviridae. There is no mortality associated with the presence of this
virus, except perhaps in salmonids (Reno and Nicholson, 1981). Cod inoculated
with this virus developed the disease within one month, remained sick for three
months, then became healthy again. In cod, this virus causes anemia and disturbs
red—blood—cell metabolism but does not lead to death (Reno et al 1986).
It should also be mentioned that when subjected to stress, cod tend to develop
exophthalmia spontaneously, as the result of gases accumulating in the eyes.
As in any other fish, exophthalmia in cod may be due to water that is
supersaturated with gases, or to a rapid rise to the surface when the fish is
captured with fishing gear. But in cod a disturbance in rearing conditions or
various forms of stress can upset the evacuation of carbon dioxide from the
choroid to the pseudobranchiae,* causing gas to build up in the eye itself
(Dehadrai, 1966). The resulting injury can cause blindness and may provide an
entry point for bacterial infection.
Parasites
Parasites are undesirable in cod farms for two reasons.
First, they can
sometimes cause death, either directly, or indirectly, by making the fish more
vulnerable to disease. Second, parasites can reduce the market value of the fish
in two ways: they make it unappealing to consumers, and they cost a lot to
remove. As is often the case for organisms in the natural environment, cod play
host to a variety of parasites (Margolis and Arthur, 1979; Margolis and Kabata,
1988).
Not the least harmful of these parasites, despite their microscopic size, are
certain protozoans. Trichodina, a ciliate of the family Urceolarlidae (40 — 100
micrometers), has been observed on the gills and in skin lesions, and has caused
20% mortality in brood stock kept in cages (Egidius and Andersen, 1984). The
flagellate Trypanosoma murmanensis, a blood parasite, can cause persistent
circulatory disorders.
In an experiment where fish were exposed to this
parasite, an increase in the abundance of Trypanosome in the blood resulted in
a drop in both hematocrit and hemoglobin. This parasite is transmitted to cod
by the marine leech Johanssonia arctica. Concentrations on the order of 105
organisms per mL have been obseri&r(gUin, 1976, 1977). This parasite is less
frequent in the Gulf of St Lawrence, where it is prevalent in 4 per cent of the
cod, than in the Atlantic (Khan et al, 1980). The microsporldian Loma morhua
has also been reported in the form—of cysts on the gills, but also on the
internal organs (Morrisson, 1983), but whether this organism causes pathology
is not known. Another protozoan, which has not been identified, seems to cause
X—cell lesions (Egidius et al, 1981; Waterman and Dethlefsen, 1982). Infection
is more common in individuals less than 40 cm long and closer to shore (2% in
Chaleur Bay, according to Morrisson et al, 1982). This parasite causes lesions
resembling tumours, generally in the pseudobranchiae.* It may also be
* Translator's note: The term "pseudobranchiae" was suggested by one of the
authors (Richard Bailey) to translate the French term "pseudobranchies". But this
equivalence could not be confirmed, because this part of the text was written
—L-
Ç,
24
responsible for a delay in tiexual maturation and a higher mortality rate
associated with bacterial infections in cod kept in captivity (Morrisson et al,
1982).
The best •'mown parasites of cod are nematodes of the family Anisakidae. The
codworm, Phocanema decipiens, starts its life cycle in seals, mainly the gray
The female codworm releases about 400 000 eggs (Odense, 1978), which seal.
hatch, at temperatures of 2 to 24°C, in 5 to 20 days. The eggs sink to the
bottom, where the emerging larvae attach themselves to the substrate. There they
can survive for up to 140 days at a temperature of 5°C. These larvae are eaten
by benthic copepods such as harpacticoids and cyclopoids, but never by plankton
such as calanoids, and they are not transmitted.directly to the fish (McClelland,
1982). These copepods in turn are eaten by cod or by other fish, such as smelt
(Osmerus mordax), on which cod feed. The larvae penetrate the cod's stomach wall
and lodge in the muscle, curled up to a size of 3 to 4 cm. When the cod are
eaten by seals, the mammals' high internal temperature triggers moulting and
maturation of the parasite (Odense, 1978). The codworm poses no danger for
humans, because it dies when the fish is frozen (24 hours at -20 °C) or cooked
(70°C for 7 minutes). Codworms are more common in the southern part of the Gulf
of St Lawrence (Odense, 1978; McClelland, 1982). McClelland et al (1983) counted
0 to 20 parasites per cod in cod measuring 20 to 80 cm. The number of parasites
increased with the size of the fish. Of the cod 20 cm long, only 20Z were
infested, but for cod 80 cm long, the rate was 100Z. P. decipiens lodges mainly
in the filets (867.), but also in the abdominal muscles (11Z) and in the coelom
(3Z). Anisakis spp., another nematode of the same family, is found less
frequently. It lodges in the mesenteries of the liver and intestines, but rarely
in the filets (only 3Z of the cases) (McClelland et al, 1983).
The crustacean Lernaeocera branchialis attaches itself to the cod's gIlls. The
intermediate stages of this parasite are found in the lump fish, Cyclopterus
lumpus, near shore, which may explain why it is mainly cod less than 50 cm long
that are affected by this parasite (sometimes as many as 15Z of the individuals).
There are rarely more than two of these parasites on each fish. Nevertheless,
the presence of this parasite seems to correlate with a disturbance in the
sexual-maturation cycle (Templeman et al, 1986). For more about this parasite,
see Rebate (1988).
DISCUSSION
Generally speaking, rearing the Atlantic cod involves many fewer unknowns than
does rearing many other marine fish. As Table 2 (starting on page 36) indicates,
a great deal is known about the biology of this fish at the various stages of
its life cycle. Part of the reason is that the first attempts to produce postlarvae for restocking purposes were made over 100 years ago. In Scotland, which
appears to have ideal conditions for rearing cod, it is believed that intensive
cod farming will present few problems, and that cod can be grown from a weight
of 5 g to a weight of 2 kg within 18 months. But mention should also be made
of a Norwegian experiment in which cod fry were raised from larvae in enclosed
ponds by a method that may well be more economical (Kvenseth and Oiestad, 1984;
Oiestad et al, 1985). In Eastern Canada, producers find it unprofitable to rear
cod from the earliest stages of life, and instead concentrate on on-growing of
juveniles taken in the natural environment (Williams and Kiceniuk, 1986; Fisher,
1988).
.1
25
The mechanisms triggering sexual maturation in cod probably do not differ from
those in other fish. But if one is planning to raise juvenile cod to market
size, one must know precisely the time at which and the conditions under which
it is likely to occur. The drawback of sexual maturation in cod-rearing
facilities is that it results in weight loss and hence reduces the quality and
volume of cod produced.
This problem has already been documented (Braaten,
1984), but solutions must still be found if we want to market cod larger than
30 to 35 cm. Up to now, the sexual maturation cycle has not been controlled in
cod, though it has been in other species. In European turbot, for example, sexual
maturation can be induced at any time of year by manipulating the fishes'
exposure to light or by injecting them with hormones. Cod have a long spawning
season, so it should be possible to capture spawners in nature and use them for
artificial fertilization, without risk of missing a season. Cod offér another
advantage: they spawn naturally in captivity. Nevertheless, any intensive codfarming operation will eventually have to develop its own brood stock, and this
requires good control over reproduction.
Though we know something about the nutritional and environmental needs of cod
larvae, we still need to learn more. Cod produce myriad small, pelagic eggs,
which yield tiny, plankton-like larvae. In this respect they are comparable to
the sole and turbot in Europe (Jones, 1984). The larval stage is critical,
because it is during this stage that mortality is highest. Three main problems
need to be solved. Firsk, the mortality rate is not the same from one batch of
larvae to another. This is due to a certain variability in the quality of the
gametes, but there are no methods for determining thé quality of cod eggs.
Second, in areas where saltwater is diluted by inflowing freshwater, incubation
is difficult. The embryos sink, which increases the risk that diseases will
spread. It may be possible to manipulate the spawners so as to adjust the
density of the eggs, and hence their buoyancy, without altering the embryos'
mortality rate.
Only partial evaluations have been done of egg and larva
survival in less saline water, and the results have been contradictory (Laurence
and Rogers, 1976; Davenport et al, 1981; Kjorsvik and Lonning, 1983). The third
problem is to find a replacement diet for cod larvae and for juvenile cod below
3.5 cm in length. To date, attempts to replace live food (which involves high
labour costs) with some kind of artificial feed have been unsuccessful
(Hjelmeland et al, 1984; Oiestad et al, 1985).
Rearing cod in the juvenile and adult stages does not present any special
problems. Cod at these stages tolerate a wide range of environmental conditions,
which is a considerable advantage for rearing operations, especially in surface
waters. Cod feed readily on fish such as herring and capelin, with excellent
conversion ratios, ranging from 2:1 to 3:1.
Unfortunately, there are very few data on the mortality rates observed in ongrowing experiments. Cannibalism is no doubt the main problem to be solved.
Cod reared in tanks develop dominance hierarchies, and the submissive individuals
in these hierarchies show low growth rates, sometimes even failing
(
1
26
to grow at ail. The individuals that do not grow may eventually be eaten by
larger individuals. The usual method of solving this problem is to regularly
segregate the fish by size class, which requires handling them. Other solutions
could be tried. One possibility would be to find a feeding schedule that met
the needs of the dominant individuals first and those of the submissive
individuals later during the same day. Another would,be to determine whether
there is some density beyond which this problem does not arise.
Increasing density alwuys entails the risk of spreading disease .. There is very
little information on cod diseases in the scientific literature. The present
authors, working at the laboratories of the Maurice Lamontagne Institute in cooperation with the Armand Frappier Institut and the School of Veterinary
Medicine in St-Hyacinthe, Quebec, are conducting a program to identify the
pathogenic bacteria and viruses that may cause problems when fish from the wild
are held in enclosures.
One problem with taking cod from the wild and raising them on fish such as
capelin is that one cannot guarantee a parasite-free product. Raising parasitefree cod in intensive rearing facilities would reduce processing costs and offer
a different product to the consumer. To reduce the incidence of parasites when
rearing wild cod, the only option is to select sizes or stocks that are
relatively free of parasites and to feed them fish or artificial feed in which
the parasites have been killed by methods such as freezing.
Attempts to rear cod along the shores of the Gulf of St Lawrence face two
potential difficulties. In wintertime, ice poses a problem. And if on-growing
is attempted on a seasonal basis, there is the problem-that in protected water
bodies such as rivers l 'estuaries, or Chaleur Bay, the salinity of the surface
water varies and is relatively low. That cod are resistant to lowenvironmental
temperatures is well known. Cod secrete a glycoprotein in the blood plasma that
lets them survive at temperatures well below 0°C. In contrast, little is known
about their ability to tolerate salinities below that of sea water. But in this
regard promising preliminary results have been obtained in tests conducted in
our laboratories in co-operation with the University of Quebec at Rimouski and
the oceanology branch of Quebec's Institut National de la Recherche Scientifique.
In these tests, cod survived when transferred to water of medium salinity (7,
14, and 21 g/L) at various times of year, but when transferred to water of lover
Tests are now being done at higher temperatures, and the salinty,omed.
differences in growth rates between these two treatments Must still be compared.
Subject to this caution, we can still conclude that estuarine and coastal
environments are suitable for rearing cod as far as salinity levels are
concerned. More generally, it seems reasonable to suppose that though marine
fish normally live in water with a salinity close to 32 g/L, they could very well
live in less saline water. This suggests various possibilities for using warmer
water (sea water diluted with warmer freshwater) or for selecting rearing sites
along the coast.
Like the rest of Canada, Quebec is an exporter of fish, and is therefore subject
to international market forces. Any fluctuation in world markets, be it in the
à
27
supply of marine products or in the demand for the, has a direct impact on the
Quebec fishery. SinCe fish farms in Quebec would be serving to complèment this
fishery's production, they would be subject to the same market pressures.
At present the world catch of cod has stabilized, while demand has fallen over
the past few years as consumers have resisted excessively rapid price increases.
This combination of conditions has been quickly translated into a drop in the
market price of cod. This downtrend may give way to more stable prices once
inventories have returned to normal levels.
In Quebec, the cod catch has decreased, large cod have become scarce, and the
growth rate of the cod stocks has fallen, all of which points to a possible
market for artificially reared cod.
Little microeconomic information is available on the potential profitability of
cod farming. In 1984, Jones stated that cod could not be farmed profitably in
Scotland.
In 1986, soue entrepreneurs nevertheless started up a cod farming
operation on the coast of Newfoundland (Fisher, 1988). In this facility, cod
captured at the end of the spawning period were placed in cages for on-growing
tests that ran from July to December, in other words, from the time when
*relatively warm suer temperatures promote rapid growth to the time when growth
slows down as the fish again channel their energy into the production of gonads.
The rate of mortality in transit varied with the method used to capture the fish
and the time it took to transport them from the fishing site to, the on-growing
facility. Mortality occurred mainly during the first two weeks after capture.
The cod received meals equal to about 6% of their body weight and were fed
approximately once every two days, generally on capelin or other fish. The
results of these tests are hard to evaluate, because several factors were not
controlled. Density varied froc one cage to another. Individuals were not
segregated by size, which resulted in cannibalism. In addition to the meals
provided them, the cod were able to feed on crustaceans and fish that were small
enough to pass through the mesh on the aides of the cages. There were other
uncontrolled factors as well.
In these tests, cod that measured 47.3 cm
(1.07 kg) in July measured 53.2 cm (1.89 kg) in September and 56.8 cm (2.02 kg)
in December (Fisher, 1988). Operations of this type offer some promise, and
Cantin and Bourdages (1989) have examined their feasibility in Quebec.
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("'
36
Table 2.
A.
Summary of the biological characteristics of the life
cycle of the Atlantic cod.
Embryo
Size of egg:
1.2 - 1.6 mm.
Incubation:
Pelagic.
(Shelbourne 1964, Thompson and Riley 1981,
Kjorsvik and Lonning 1983, Howell 1984, Solberg
and Tilseth 1984).
Duration a function of temperature.
(Laurence and Rogers 1976, Thompson and Riley
1981, Kjorsvik and Novikov 1986).
Development:
Normal between 1 and 12°C.
(Thompson and Riley 1981, Iversen and Danielssen
1984, Makhotin et al 1984, Kuftina and Novikov
1986).
Varies with light levels.
(Solberg and Tilseth 1984).
Tolerates brackish water.
(Laurence and Rogers 1976, Davenport et al 1981,
Kjorsvik et al 1984).
t.
I
r'
37
B. Larva
Size when hatched
4.5 mm/200 micrograms
(Olafsen, 1984)
Development
Metamorphoses in 44 days at 10°C and 52 days at 7°C
(Laurence, 1978)
Food
Yolk sac for 7 days; food from external sources starting
on 4th or 5th day
(Laurence, 1978; Gamble and Houde, 1984; Yin and Baxter,
1987a)
Rotifers, nauplii and metanauplii of Artemia spp.
(Howell, 1973, 1984; Thompson and Riley, 1981; Solberg and
Tilseth, 1984; Tilseth and Ellertsen, 1984)
Size of prey varies with size of larvae
(Lough, 1984)
Consumes from 1 to 3 or 4 nauplii per hour
(Tilseth and Ellertsen, 1984)
Mortality
Survival rate
10% until metamorphosis, 5 to 7% after 72 days, and up to
50% (Howell, 1984; Kvenseth and Oiestad, 1984; Oiestad et
al, 1985)
Factors
Inadequate diet, cannibalism
(Howell, 1984)
Temperatures over 16 to 18°C and salinity concentrations
below 2 to 3 g/L
(Yin and Blaxter, 1987b)
îlo>
38
C.
Juveniles and adults
Size at metamorphosis * 10 to 12 mm and 1000 to 1800 micrograms (dry weight)
(Laurence, 1978; Rvenseth and Oiestad, 1985; Oiestad et
al, 1985)
Food
Accept pellets starting at 2.5 to 3.0 cm
(Bromley and Sykes, 1985)
Glycine and alanine trigger feeding behaviour
(Ellingsen and Doving, 1986)
Cannibalism
Depends on size
(Waiwood and Majkowski, 1984; Bromley and Sykes, 1985)
Depends on ration
(Oiestad et al, 1985)
Oxygen consumption
Measured according to fish's weight
'temperature
(Saunders, 1963; Braaten, 1984)
and
ambient
Measured according to timing of meals
(Soofiani and Hawkins, 1982)
Base ration
Determined according to weight of fish
(Jones and Hislop, 1978; Jobling, 1982; Braaten, 1984)
Determined according to temperature
(Hawkins et al, 1985)
Amount of food
ingested
Increases with fish's body weight
(Jobling, 1983)
Decreases with temperature
(Saunders, 1963)
Varies with feeding schedule
(Braaten and Gokstad, 1980)
e
4
'.`
•-'
• ••
39
C.
Juveniles and adults (continued)
Rate of digestion
Varies with temperature
(Tyler, 1970)
Conversion ratio
Highest when cod fed an intermediate amount of rations
(Edwards et al, 1972)
Decreases with size of fish
(Jones and Hislop, 1978; Jobling, 1982)
Varies with diet
(Howell, 1984)
Energy cost of assimilation varies from 3 to 20 per cent
of the energy ingested, (Soofiani and Hawkins, 1982)
Growth
Rapid (size of 34 cm In 60 weeks)
(Braaten, 1984; Howell, 1984; Oiestad et al,
Williams and Riceniuk, 1986)
1985;
Fastest at 13 to 15 °C
(Tyler, 1970; Jobling, 1983)
Increases with ration
(Edwards et al,
1972; Jones and Hislop, 1978;
Braaten, 1984; Hawkins et al, 1985; Houlihan et al, 1988)
Decreases with size (2% per day for fish less than 90 g;
0.2% per day for fish over 800 g)
A
"
c
■
er
•
40
C.
Juveniles and adults (continued)
Diseases
Vibriosis (fatal)
(Egidius and Andersen, 1984)
Viral erythrocytic necrosis
(Reno and Nicholson, 1981; (Reno et al, 1986)
Exophthalmia
(Dehadrai, 1966)
Parasites
Trichodina spp. (fatal)
Egidius and Andersen (1984)
Trypanosoma murmanensis
(Khan, 1976, 1977)
Loma morhua
(Morrisson, 1983)
Phocanema decipiens (codworm)
(Odense, 1978; McClelland, 1982; McClelland et al, 1983)
Lernaeocera branchialls
(Templeman et al, 1976; Kabata, 1988
Behavlour
Hierarchies and aggressiveness
(Brawn, 1961a)
»
.-%‘ •
#
e
4 f
41
D.
Sexual maturation
Size at sexual
maturity
Less than 10Z of cod are sexually mature at 30 cm; all
cod are sexually mature at 50 cm.
(Beacham, 1983 a and b; Baird et al, 1986)
Growth
Cod lose weight during sexual maturation.
(Braaten, 1984)
Spawning season
From January to June in the Atlantic, May to autumn in
the Gulf of St Lawrence
(Fowles, 1958; Fahay, 1983; Scott and Scott, 1988)
Fecundity
Very high
(May, 1967)
Artificial
fertilization
Usual techniques
(Shelbourne, 1964; IversenandDanielssen, 1984;Kjorsvik
and Lonning, 1984)
Natural fertilization Spontaneous in tanks or ponds
(Laurence and Rogers, 1976; Jones, 1984)
Gametes released over a period of 2 to 3 weeks
(Shelbourne, 1964; Holdway and Beamish, 1985)
Behaviour
Hierarchies and aggressiveness
(Brawn, 1961 a and b)