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FISHERIES RESEARCH BOARD OF CANADA
TECHNICAL REPORT NO.
1971
243
_Of_
FISHERIES RESEARCH BOARD OF CANADA
Technical Reports
FRS Technical Reports are research documents that are of sufficient
importance to be preserved. but which "for some reason are not appropriate for
primary scientific publication. No restriction is placed on subject matter and the
series should reflect the broad research interests of FRB.
These Reports can be cited in publications, but care should be taken
to indicate their manuscript status. Some of the material in these Reports will
eventually appear in the primary scientific literature.
Inquiries concerning any particular Report should be directed to the
issuing FRB establishment which is indicated on the title page.
~
FISHERIES RESEARCH BOARD OF CANADA
TECHNICAL REPORT No. 243
SABLEFISH CULTURI: - PROGRI:SS IN 1970
by
W.A. Kennedy and M.S. Smith
FISHERIES RESEARCH BOARD OF CANADA
Biological Station. Nanaimo. B. C.
March 1971
INTRODUCT ION
Experimental culturing of sablefish (blackcod, Anoplopoma fimbria) as
described in Technical Reports Nos. 107 and 189 continued through 1970.
The objective remained unchanged, namely to assess, from a biological viewpoint, the feasibility of a corrrnercial operation based on capturing juvenile
sablefish and rearing them to corrrnercial size for slaughter.
The equipment and methods were essentially as described in Technical
Report No. 107. However, the tanks were located indoors in 1970. Also,
since the summer of 1969, tank covers had been removed whenever a new phase
of the experiment was started, so during 1970 all tanks were without covers
except the one used for Batch 3 (terminated July, 1970).
Fish Procurement
1119.
Details on fish procurement in 1970 are given in Manuscript Report No.
Highlights are:
1. Juvenile sablefish seem procurable without fail in late spring and
all summer in the vicinity of Port Hardy.
2. They can be caught in quantity with baited hooks, either on longlines or on hand lines.
3.
Most of the juvenile fish that are readily available have had one
birthday (mid-winter) and are about 1-1/2 years old when taken. However, a
few are a year older.
4. They can be successfUlly transported aboard ship in fibreglas tanks
with water·tight lids. The tanks must be kept filled to the top, to avoid
surge, by a continual flow of freshly pumped sea water. The water must be
aerated by forcing compressed air through airstones. At 40 grams of fish
per liter of water (0.4 pounds per gallon), they are not overcrowded.
~.
It is desirable that the sea water used be colder than
l~oC (~9°F).
Length I Weight and Girth
During fish procurement, a random sample was taken of the juvenile
sablefish caught at Port Hardy, and individual weights, fork lengths and
girths were determined. Manuscript Report No. 1119 gives equations that
express the relationship between: (1) length and weight; (2) length and
girth; and (3) weight and girth. The length-weight relationship is essentially the saine as that reported in Technical Report No. 74, I.e. essentially the sam'3 as for sablefish of all sizes from the Gulf of Alaska, from
La Perouse Bank, and from waters off Oregon.
On the basis of length-girth and weight-girth relationships, the minimum size of sablefish expected to go through the web of a net of a given
- 2 -
mesh size or through a pipe of a given size were calculated and tabulated in
Manuscript ReportNo. 1119. It is of particular interest to potential sablefish culturists that a typical sable fish 10 inches (254 millimeters) long,
weighing 11 ounces (150 grams), cannot escape through the web of a net of
2~1/4 inch (57 millimeter) mesh, stretched meaSure, or through a pipe of
1-1/2 inch (38 millimeter) inside diameter. Our experience ind icates that
almost all of the juvenile sablefish available are more than 10 inches long.
Tags and Brands
Some "tied-on" tags (described in Technical Report No. 107) that had
been applied in 1969 were still attached in 1970. Otherwise, the fish used
were untagged.
Brands were applied to a number of sablefish -- but none to fish used
in important experiments. The technique used was a modification of that
described by Mighell (1969). Each "branding iron" was in the form of a
number, 3/4 inch (l9 millimeters) high, formed from brass and fixed at
right angles to a handle. To apply a brand, a branding iron that had been
cooled by inmersion in liquid nitrogen was held against the skin of an anaesthetized fish for a few seconds (5 seconds seem best). Brands were applied
in combination to produce a 3-digit number on the left side of the fish
above the lateral line just behind the head.
A few of the first brands applied were still legible after ten months,
most were not.
Dissolved Oxygen
A crude experiment was conducted to find the minimum concentration of
dissolved oxygen at which sablefish survive. The experiment consisted of
keeping a fish in a sealed container fUll of sea water until it died from
insufficient oxygen (about 3 hours), then finding how much oxygen was left
in the water in the container. On the basis of two trials, it appears that
at l2°C (54°F) a 500 gram (1 pound) sablefish needs a minimum of almost one
part per million of oxygen dissolved in its water to survive.
A number of determinations of oxygen concentration made on September 1,
2 and 3 indicated that:
1. Oisso1 ved in the sea water as it entered the fish tanks were about
8 parts per million of oxygen; being l2°C it was therefore about 80% saturated with dissolved oxygen.
2. There were 6-7 parts per million of dissolved oxygen in the less
crowded tanks and 5-6 parts per million in the more crowded. Obviously, the
fish were using oxygen faster than the airstones (With which all tanks W-2re
equipped) could supply it, and tanks with more fish used more.
3.
When the sea water supply to a tank was interrupted {but with
- 3 -
airstone(s) on), the amount of dissolved oxygen decreased, rapidly at first
then more and more slowly, until, after several hours, it stabilized at a
lower concentration. Apparently, the new level at which oxygen concentra~
tian stabilized represented the level at which the airstone(s) coulo supply
oxygen as fast as ttle fish used it. Presumably, when there is less oxygen
dissolved (a) further oxygen dissolves more readily and (b) the fish use
less. The oxygen concentration stabilized at about 2 parts per million in
the most crowded tank (2 airstones) and at slightly higher values in less
crowded tanks. In other words, a tank of sablefish should survive for many
hours after a water failure if aeration by compressed air through airstones
is adequate.
4. On the other hand, without compressed air a water failure would.
soon kill all the fish -- in about 2 hours in crowded tanks.
5.
Adequate aeration (assuming clean tanks) probably requires one
airstone in a tank with less than 100 kilograms (220 pounds) of sablefish,
two airstones in a tank with 100-200 kilograms (220-440 pounds), etc. Each
airstone should use about 3 cubic feet (0.08 cubic meters) of compressed
air per hour.
Herring was one of the two main kinds of food used, and it was always
used with some other kind of food. It was usually purchased in small boxes
containing about 5 pounds (2 kilograms) each of herring frozen together.
They were used between December and May after being stored for a relatively
short time, and between June and November after having been stored since Moy
or earlier. Most of the herring used during December 1970 was caught by a
cormlercial seiner under goverrunent charter for exploratory fishing and was
processed at Nanaimo by Biological Station personnel. Processing consisted
of filling cardboard boxes that were 6 x 12 x 14 inches (16 x 31 x 36 centimeters) with herring, then freezing theill. The resulting block of froze"
fish was later cut by bandsaw into pieces weighing 5 pounds (2 kilograms) or
less.
Dogfish was the other main kind of food used; most of it was caught and
processed by Nanaimo Station personnel, but some used in December was caught
and processed commercially. In most cases (whole dogfish) the entire fish
was used, but a limited quantity of carcasses were prepared with head and
viscera removed (dressed dogfish). Both forms of dogfish were packed in
6 x 12 x 14 inch cardboard boxes shortly after capture (except that those
processed commercially were 3 days after), then frozen, the end product
being a block of dogfish frozen together. later a bandsaw was used to cut
the blocks into "bite-size" chunks of from 1 cubic inch to 10 cubic inches
(16 to 160 cubic centimeters).
A minor food was mussels, gathered locally by Nanaimo Station personneL
Some were fed raw, along with pieces of shell, after crushing. Others were
steamed briefly, then removed from the shell; steaming hardens the meats ar,c
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also causes the shells to gape. Mussels were used in both forms, both
fresh and frozen. The recorded amounts of mussel used indicates mussel
meats only, without shell.
Another minor food was "O.P. cake" made by mixing 69% Oregon moist
pellet with 31% water. Several pounds of the resulting mixture was shaped
into a "cake" about one inch thick and frozen. Later the frozen "cake" was
cut or broken into oieces of about one cubic inch (16 cubic centimeters).
"U.V. cake" was prepared and used in exactly the same way, except that
the mixture consisted of 68% "powder," 31% water and 1% binder (carboxymethylcellulose). The "powder" was supplied by Drs. A.J. Wood and T .0.0.
Groves, Department of Biochemistry, University of Victoria, who described it
as the dietary equivalent of Oregon moist pellet.
Another food was "chicken-scrap" -- also supplied by Drs. Wood and
Groves. It consisted mainly of parts of chicken not used for hUllan constunption (but no viscera or feathers) with minor ingredients added to make a
"complete ration." The minced chicken material, frozen and encased in
plastic, was supplied as cylinder& about 6 inches in diameter aoo about 2
feet long (l~ centimeters and 60 centimeters). We removed the plastic
casing and cut the frozen material into pieces of about 3 cubic inches (50
cubic centimeters) which were kept frozen until used.
Feeding procedures and Sablefish Reaction to Foods
Herrings were sometimes used while still frozen together into a :> poune
or smaller mass, and sometimes after thaWing enough to separate individuals.
A frozen mass of herring floats, and as it thaws sablefish tear away protruding heads and tails or take whole herring as they become loose. Separated
herring sink and sablefish usually swallow them whole, either while they are
sinking or when they are on the bottom of the tank. Occassionally a herring
is too big to be swallowed; unless satiated one sablefish after another will
take such a herring in its mouth and shake it until a piece is worried off
and swallowed.
Dogfish were stored as "bite-size" chunks, which were used while still
frozen or partially thawed. The chunks sink and sablefish swallow them
either while they are sinking or when on bottom. Occasionally a piece is
too big to be swallowed, but, if hungry, sablefish will gradually worry
pieces from it until it is gone. They usually do not eat fins or pieces of
liver if detached, but they do readily eat chunks that include fins or
liver. After dogfish chunks are fed, the water becomes murky with oil and
organic particles, but the sablefish appear unaffected by the murkiness.
Mussels were fed in various forms. 5ablefish eat them without en'thusiasm and eat much less than if other food is offered. They gain little on
a diet of mussels. It would seem that mussels are not a suitable food for
culturing sablefish.
- 5 -
"O .. P. cake," ·U.V. cake" and "chicken-scrap" were fed to sablefish as
frozen "bite-size" chunks. Chunks of all three foods float at first, then
sink as they thaw. Sablefish seldom eat them while they are frozen solid
(Le. still floating), but do eat them when the outside has softened slightly by thawing but while the chunk is still frozen enough to hold it together
(Le. while sinking or on the bottom). If too many chunks are fed at one
tim~J some will thaw and disintegrate before they can be eaten.
Sablefish
probably get no nourishment from them after they disintegrate. The water
gradually becomes murky at feeding time because of material lost from the
chunks as th~y thaw) but the murkiness seems to have no adverse effect on
the sablefish.
In contrast to many fish that are cultured, the sablefish show only
m:xl.erate excitement when fed. They never show agressive behaviour to one
another, not even while feeding. Very seldom do two fish :nouth the same
piece of food, and when they do there is no obvious conflict.
A partial report on Batch 3 appears in Technical Report No. 189. Batch
3 was started on January 15, 1969 and consisted originally of 30 fish that had
been cau3ht by trawl aboard "A.P. Knight" near Navy channel on January 8.
All were tagged with "tied-on" tags (see Technical Report No. 107). By the
end of 1969 only 6 still had tags and only 4 by July, 1970.
By Decemoer 16, 1969 there were 26 fish whose total weight was 63.54
kilograms (140 pounds) j they had gained 43.34 kilograms (95.5 pounds) since
the start or 0.15 kilograms (0.33 pounds) per fish per m:>nth. By May 14,
1970 there were 25 fish whose total weight was 77.22 kilograms (170 pounds).
They had gained a total of 15.65 kilograms (34.5 pounds) since December, Le.
0.13 kilograms (0.28 pounds) per fish per month. They had gained 0.15 kilograms (0.33 pounds) per month since the Batch was started.
Batch 3 was discontinued on July 17, 1970 when there were 22 fish that
weighed a total of 63.60 kilograms (140 pounds). The survivors had lost
0.10 kilograms (0.25 pounds) per fish per month since May. The loss in
weight and the greater mortality (1.5 fish per m:>nth compared with 0.3 earlier) between mid May and mid July is attributed to higher water temperatures
(discussed later).
Batch 3 was fed nothing but frozen herring and frozen dressed dogfish,
one or the other being offered exclusively at any given feeding. Between
Januuy 15, 1969 and May 14, 1970 their food consisted of 58% herring and
42% dogfish, and they ate about 90% of the food offered. For that period
they gained close to one kilogram for every 5 kilograms of food used .•
*
Amount gained per amount of food is the weighted mean of the amount of
food offered, whether eaten or not, during a given month, divided by the
amount gained during the month by the fish that survived until the end of
the month.
- 6 -
A partial report on Batch 6 appears in Technical Report No. 189. Batch
6 was started on August 14, 1969 with fish that had been caught by baited
hooks at Minstrel Island June 13-16. The Batch consisted initially of 35
fish weighin; a total of 17.96 kilograms (39.5 pounds).
By October 15, 1969 after five deaths attributed to injuries received
during capture, there were 30 fish weighing a total of 21.84 kilograms (48
pounds). All 30 survived until June 16, 1970 when their total weight was
54.65 kilograms (120 pounds). They had gained 32.81 kilograms (72 pounds)
between October and June, i. e. 0.14 kilograms (0.30 pounds) per fish per
month.
By September 15, 1970 there were 27 fish whose total weight was 51.14
kilograms (113 pounds). The survivors had gained about 0.02 kilograms
(0.04 pounds) per fish per month since June. Slower growth and greater
m:ntali ty (1 fish per month during swvner compared with 0 fish per month
earlier) are attributed to higher water temperatures.
By December 15, 1970 there were 26 fish ""hose total weight was 57.86
kilograms (127 pounds). The survivors had gained 8.27 kilograms (18 pounds)
since mid September, Le. 0.11 kilograms (23 pounds) per fish per month.
Durirly the two cold water periods combined, they gained 0.13 kilograms (0.28
pounds per fish per month).
Batch 6 was fed a variety of foods. Between October 15, 1%9 and June
16, 1970 it consisted of 93% herring, 2% shrimp waste meal, and 5% mussels,
only one kind of food being used on any given day. They were given 5.8
kilograms of food per kilogram gained. Between September 15, 1970 and
December 15, 1970 their food consisted entirely of chicken waste. They were
given 6.5 kilograms of food per kilogram gained. During the two cold weather
periods combined, they were given 6.0 kilograms of food per kilogram gained
and ate about 90% of it.
During the swnmer of 1970 they were fed 74% herring, 14% "O.P. cake,"
6% "chicken waste," 4% "U.V. cake" and 2% mussels. Food conversion during
the period was not assessed because poor growth makes it meaningless.
A partial report on Batch 7 appears in Technical Report No. 189. Batch
7 was started on September 17, 1969 with fish that had been caught by baited
hooks at Minstrel Island June 13-16. The Batch consisted initially of 35
fish weighing 27.00 kilograms (59.4 pounds).
By May 14, 1970, after three deaths in late 1%9 from obscure causes,
there were 32 fish weighing a total of 58.24 kilograms (129 pounds). The
survivors had gained 33.02 kilograms, Le. about 0.13 i<ilogral'i1;; (0.29
pounds) per fish per month since September 1969.
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By September 15, 1970 there were 27 fish weighing a total of 51.66
kilograms (114 pounds). The survi vars had gained about 0.02 kilograms
(0.05 pounds) per fish per month since May. Slower growth and greater
mortality (1.2 fish per month during the sununer compared with 0.4 fish per
month earlier) is attributed to higher water temperatures.
By December 15, 1970 there were 24 fish whose total weight was 55.62
kilograms (122 pounds). The survivors had gained 8.59 kilograms (19 pounds)
since mid September, Le. 0.12 kilograms (0.26 pounds) per fish per month.
During the two cold weather periods combined, they gained 0.13 kilograms
(0.28 pounds) per fish per month.
Batch 7 was fed nothing but chu:lks of whole (Le. including viscera and
heads) frozen dogfish. Between September 15, 1969 and May 14, 1970, they
were given 4.5 kilograms of food per kilogram gained. Between September 15
and December 15, 1970, they were given 4.6 kilograms per kilogram gained.
During the two cold water periods combined, they were given 4.5 kilograms
of food per kilogram gained and ate a!:>out 90); of it.
Food conversion during the summer was not assessed because of poor
growth.
A partial report on Batch
8 was started on September 17,
hooks at Minstrel Island, June
fish weighing a total of 25.87
8 appears in Technical Report No. 189. Batch
1969 with fish that had been caught by baited
13-16. The Batch consisted initially of 35
kilograms (57 pounds).
By May 14, 1970 a fter two deaths from obscure causes in the spring of
1970, there were 33 fish weighing a total of 60.81 kilograms (l34 pounds).
The survivors had gained about 0.14 kilograms (0.30 pounds) per fish per
month since September, 1969.
By September 15, 1970 there were 22 fish weighing a total of 43.74
kilograms (96 pounds). The survivors had gained about 0.04 kilograms (0.08
pounds) per fish per month since May. Slower growth and greater mortality
(2.8 fish per month during summer compared with 0.2 fish per month earlier)
are attributed to higher water temperatures.
By December 15, 1970 there were 21 fish whose total weight was 49.26
kilograms (lOB pounds). The survivors had gained 7.85 kilograms (17 pounds)
since mid September, L e. 0.12 kilograms (0.28 pounds) per fish per month.
During the two cold water periods combined, they gained 0.13 kilograms (0.33
pounds) per fish per month.
Batch 8 was fed nothing but chunks of whole (Le.
head) frozen dogfish and whole frozen herring, only one
given day. Between September 15, 1969 and May 14, 1970
4.4. kilogra!1ls of food per kilograll gained, and between
including viscera and
kind being fed on a
they were given
September 15 and
- 8 -
December 15, 1970 they were given 5.9 kilograms of food per kilogram gained.
During the two winter periods combined, they were given 4.8 kilograms of
food per kilogram gained.
Their food consisted of 45% herring and 55% dog-
fish, and they ate about 90% of it.
Adverse Effects of High Temperatures
In this section the word "summer" means Mtha period between mid May and
mid September," and the word "winter" means the rest of the year.
It was notable that in 1970 Batches 3, 6, 7 and B all grew decidedly
slower and had higher mortality rates during summer than during winter.
These adverse effects are attributed to higher water temperatures during
summer, because, excluding dissolved oxygen (which is dependent on temperature) no environmental condition changed in phase with the sunvner vs. winter
changes except water temperature. Some water temperatures are given in
Table 1, and it is ap"arent that surrrner temperatures are indeed distinctly
higher than winter temperatures.
Temperatures during earlier summers were much like those shown in Table
1 for 1970. Unfortunately, comparisons between S\Jl'1\,1ler and winter growths
and mortalities during earlier years is complicated by such things as: suspected adverse effects from tags, from deficient diets and from handling at
time of capture. Nevertheless, comparisons were made and showed that Batch 2
in 1969 and Batch 1 in 1968 had also grown slower, and experienced greater
mortality during sur.uner than during winter.
But on the other hand Batch 3 in 1969, Batch 2 in 1968 and Batch 1 in
1967 had neither grown slower, nor had higher mortality rates in summer than
in winter. Also 1n four lots of fish used for cro~ding experiments in 1969,
growth was about the same in surnmer and winter (their mortality rates were
not compared because of possible distortion from tagging mortality and postcapture mortality).
Further examination showed that the average weight of individual fish
exceeded l.8 kilograms (4 pounds) at the beginning of sunmer* in each of:
Batches 3, 6, 7 and 8 in 1970, Batch 2 in 1969 and Batch 1 in 1968. Average
weight was less than l.8 kilograms at the beginning of summer in each of:
Batch 3 in 1969, Batch 2 in 1968, Batch 1 in 1967 and the cro~ing experiment
lots in 1969. Thus, among 6 lots of fish with average weights of more than
*
This statement is strictly true only if "summer" for Batch 6 is defined as
starting in mid June rather than mid May. Batch 6 averaged less than l.8
kilograms at mid May, and growth and mortality rates remained Winter-like
until mid June. But by mid June, Batch 6 averaged over 1.8 kilograms and
growth and mortality rates then became summer-like.
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1.8 kilograms, growth was slower and mortality greater during summer than
during ovinter. Among 7 lots of fish with average weights of less than 1.8
kilograms, there was no difference between surruner and winter. There are no
other appropriate data. Therefore, it would seem that large sablefish (over
1.8 kilograms) are adversely affected by high swruner water temperatures,
whereas small sablefish (under 1.8 kilograms) are not.
The average growth rate of all large sablefish since the project began
has been 0.11 kilograms per fish per month during winter and 0.01 kilograms
per fish per month auring summer. Their average mortality rate has been
0.44% per month during winter and 1.33% per month during summer.
To avoid the adv~rse effects of high temperature on large sablefish,
it would tentatively appear desirable to use water colder than 12°C (:>4°F)
or even lOOC (500F). In late sU!TL'Tler, after the fish are acclimated to
higher temperatures, a degree or two higher might be acceptable.
The general procedure for Batches 1-8 has been to establish about 30-1:>
fish in an 8 foot (2.4 meters) diameter tank and to keep the group intact
throughout the experiment except for decrease by natural death. Because
growth rate has been much greater than mortality rate, th~ biomass (Le.
total weight of all the fish in the Batch) typically has increased from
about 20 kilograms (45 pounds) to about 100 kilograms (220 pou'1ds) during an
experiment.
A new procedure was initiated with Batch 9, namely to keep the biomass
approximately constant (at about 1:>0 kilograms or 330 pounds) by removing
individual fish periodically to compensate for growth. The new procedure
more nearly resembles probable practice in a corrrnercial operation where
tanks would presumable carry as many fish as possible consistent with good
growth and low mortality, "thinnings" being transferred to other tanks.
AlSO, although every fish in Batches 1-8 was weighed each weigh-day (usually
every month), only a representative sample of Batch 9 was weighed every
weigh-day.
In the 8 foot diameter tank used, the water was usually about 2 feet
(60 centimeters) deep, so 1:>0 kilograms of fish represents a cro·Nding rate
of 31 kilograms per square meter (6.4 pounds per square foot) or about :>0
grams per liter (1/2 pound per imperial gallon). At the time Batch 9 was
set up, it seemed that was about the optimum rate of crowding (see Technical
Report No. 189).
Batch 9 was set up on September 1:>, 1970 with fish that had been caught
by baited hooks from M/V ~ at Fort Rupert (near Port Hardy) about
August 27, 1970. Most earlier Batches were not set up so soon after capture,
beca'.Jse mortality is always much heavier for the first 6-8 weeks than subsequently -- presumably because of injuries and adverse conditions associated
with capture. Batch 6 fish were no exception and mortality was comparatively
- 10 -
high until mid November.
On September 15, Batch 9 consisted of 373 sable fish. A representative
sample of 42 fish weighed 26.46 kilograms, so the biomass must have been
a.oout 234 kilogra:ns (510 pounds) at that time. It had become considerably
greater than the specified biomass of 150 kilograms mainly because of both
faster growth and lower mortality than expected. In order to reduce the
biomass to the specified value, the 139 smallest fish were removed on
September 23. To select the smallest, all fish were anaesthetized and
measured, and those shorter than an appropriate predetermined length were
removed while those longer were returned to the ta,k.
Removal of 139, plus 39 deaths (part of the heavy post-capture mortality)
reduced Batch 9 to 195 fish by October 15. On October 15 a representative
sample of 50 fish weighed 43.58 kilograms, so the biomass must have been
about 170 kilograms (374 pounds). By November 16, 17 more fish had died,
leaving 178. A representative sallp1e of 49 fish weighed 48.45 kilogra:ns,
so the biomass must have been about 176 kilogralls (388 pounds).
The biomass was therefore again reduced on November 18 by removing the
25 smallest fish. Removals plUS 3 deaths reduced Batch 9 to 150 fish by
December 15. A representative sample of 51 fish 'Neighed 60.08 kilograms, so
the biomass must have been about 177 kilograms (390 pounds) on December 15.
Had the 139 fish removed on September 23 and the 25 removed on November
16 been retained elsewhere and had growth and mortality been the same as in
Batch 9, then by December 15 the removed fish would have numbered about 132
and weighed about 151 kilograms. Thus with the 177 kilograms in the original
tank, the biomass would have been 328 or more than enough for two tanks.
The average weight of the September 15 sample was 0.63 kilograms. But
if fish of the size that were later removed from the tank on September 23
had been omitted from the sample (taking account of g:rowth), then the average
weight would have been about 0.72 kilograms. Since the average weight of the
October 15 sample was 0.87 kilograms, then the fish that remained in Batch 9
must have gained about 0.87 - 0.72:: 0.15 kilogralls per fish during the
month. Similar calculations indicate a gain of 0.12 kilograms per fish
between Oc tober 15 and November 16, and 0.15 kilograms per fish between November 16 and December 15. For the three months combined, the average gain per
fish per month was 0.14 kilogra:ns (0.30 pounds).
Counting each day that each fish lived in the tank as a fish-day, there
were 17,771 fish-days during the 91 days between September 15 and December
15, 50 the average number of fish in the tank over the whole period was 195.
From the average number of fish and average gain per fish per month, the
total increase in biomass of Batch 9 in three months is calculated as 80.4
kilograms (177 pounds). During the same three months, they were given 408
kilogralls (900 pounds) of food (7'a whole frozen herring, 28% whole frozen
dogfish) of which they ate about 9~. This represents a gain of about one
kilogra.ll for every 5.1 kilograms given.
- 11 -
Discussion of Batches 3, 6, 7 z 8 and 9
Data on the Batches are surrunarized in Table 2. The rate of gain in cold
water is remarkably consistent at about 0.13 kilograms (0.29 pounds) per
fish per month regardless of the kind of food used. The rate of gain in
warm water was less consistent, but in all Batches it was dramatically less
than the rate in cold.
In spite of considerable variation between Batches, mortality rate was
obviously higher in warm water than in cold. In cold water, mortality
averaged slightly less than 1% per month.
The amount of food needed to put on a given weight was least when the
food was dogfish only, medium when it was partly dogfish, and most when i t
included no dogfish. So sablefish seem to gain more per unit weight of food
on dogfish than on other foods. However, the ratio did not differ by much
from one kilogram (pound) gained for every 5 kilogralls (pounds) of food used
on any of the diets used. Because only about 90% of the food used was actually eaten, the food conversion factor was about 4.5.
Crowding
Experiment~
An e..<perime:"lt designed to study the effects of crowding on growth and
mortality was started in June 1969 and continued into 1970. Results to the
end of 1969 are reported in Technical Report No. 189. Because of mishaps
in 1970, results after December 1969 are too fra3mentary to warrant reporting
in detail. They did tend to support the 1969 findings that sab1efish grow
better when moderately crowded than when uncrowded.
A new crowding experiment was set up on September 15, 1970. Agai"l,
four oval tanks were used in which conditions were identical except for
amount of fish. The tanks were stocked initially with 10, 20, 30 and 40
kilograms of fish respectively. The biomass in each tank was thereafter
kept at approximately 10, 20, 30 and 40 kilograms respectively by removing
individual fish at the time of mid-Inonth weighings to offset the a'TlOU'1t by
which biomass ha:;l increased by growth. They were fed dogfish and herring in
about equal proportions and given all they would eat.
The fish used were mostly from a lot caught by M/V A. P. Knight at Port
Hardy about May 18, 1970 with a few from a lot caught by M/V A. P. Knight
at Port Hardy about July 13, 1970. Their weights on September 15 ranged
from 0.3') to 1.26 kilograms and averaged 0.7'j kilograms (1.66 pounds). None
had previously been used in experime"'lts.
Growth and mortality at four rates of crowding are shown in Table 3.
\'Iithin the range tested, both growth and mortality seem to be independent
of rate of crowding.
The bottom area of each tank used was 10 square feet (0.929 square
meters), a.,d they normally hold about 125 imperial gallons (567 liters) each.
Therefore, a crowding rate of 40 kilograms per tank represents 43 kilograms
- 12 -
per square meter (8.8 pounds per square fo::>t) or about 70 grams per liter
(0.7 pounds per imperial gallon). Probably, bottom area is more relevant
than volume of water.
Impounded Sablefish
As in 1969, tne floating pound was used only for holding fish that had
already been used in experiments in case there should be further need for
them. Of 21 sable fish (formerly Batch 2) put into the pound on Septe:nber 16,
1969, only 2 were still alive on May 26, 1970. On JU"lC 3, 38 sable fish were
put into t',e pound as Vlere 22 on July 17, both lots having been recently
weighed and branded. Out of the 62 fish, only 29 were alive on OCtober 14,
6 deaths having occurred in June, 2~ in July and 2 in August. The survivors
were weighed on October 14, and the 2~ whose branded numbers could still be
read were found to have gained 0.05 kilogra1ls (0.11 pounds) per fish per
month since early slUn...."er. Two had reached corrmercial size and were butchered.
On November 25, the 7 biggest fish were removed and J<illed to provide
esophagus measurements (see next section). They were weighed after death,
and in the process of selecting the biggest ones, lengths of all fish in the
pound were lneasured. The 7 biggest fish (identified from their brands) had
gain~d 0.28 kilograms per fish per month since October 14.
Estimating the
weights of the remainder from their lengths and comparing with actual weights
on October 14, indicates that they gained about 0.30 kilograms per fish per
month in the interval. Four fish withdrawn for special measurement in January, 1971 (identifiable by their brands) had gained about 0.31 kilograms per
fish per month since October 14. Thus it would seem that during the winter
of 1970-71, the impounded fish are gaining about 0.30 kilograms (2/3 pound)
per fish per month, Le. are growing at least twice as fast as those in
tanks. There was no mortality between October 14 and November 28, 1970.
The poor growth and high mortality among fish held during the swnner is
consi'itent with events in the ta'1ks. The unusually high summer mortality in
the pound probably resulted from higher temperatures in the pound than in
tanks. There is no obvious explanation for the high mortality during the
winter of 1969-70 unless it was a delayed adverse effect from earlier tagging.
The extravrdinary growth rate observed recently in the pound indicates
that the possibilities of pounds for rearing sablefish must be re-examined.
Esophagus Diameters
For the development of suitable rations, it is useful to know the
biggest chunk of food that a sable fish of a given size can swallow. Obviously, an important factor is the size of the narrowest place along the route
from :nouth to stomach. Measurements along the route showed that it ..... as
narrowest where the esophagus is prevented from stretching as much as it
otherwise would by the pectoral girdle (a "ring" of bones that support the
pectoral fin). "Esophagus diameter" as used here means the inside dianeter
- 13 -
at that place.
To measure esophagus diameter, the fish'
5
head was cut off and a slight-
ly truncated wooden cone was pushed, small end first, d:>wo the esophagus as
far as it would go without forcing. The place on the cone where its diameter
became large enough to prevent further penotration was marked. The cone was
then withdrawn and its diameter at the mark was measured by calipers and
recorded.
The recorded measurement is the "esophagus diameter" as defined above.
The fish is unable to swallow a piece of food of larger cross secti'On. Observations on feeding sablefish indicate that they probably do swallow pieces
as big as they can swallow. Therefore, the recorded esophagus diameter indicates the maximum size of food chunks swallowed.
Esophagus diameters were measured on 72 fish. When diameters were plotted against fork length on log log graph paper, the points tended to fall
along a straight line. Because of considerable var~ance, we plan to get more
data tie fore formally fitting a line. A few values from a line fitted by eye
are as follows:
Fork. Length
Esophagus
Diameter
Inches
Millimeters
Inches
Millimeters
Smallest size captured for rearing
10.6
270
0.9
23
Typical size captured for rearing
13.4
340
1.1
27
Typical size 4 months after capture
18.1
460
1.4
35
Typica 1 size 10 months after capture
21.2
540
1.5
39
Typical size 7 months before slaughter
24.4
620
1.7
43
Typical size when slaughtered
27.2
690
1.8
47
1. Apparently juvenile sablefish suitable for rearing can be taken
without fail at Port Hardy from May to August.
2.
Baited hooks will catch them in quantity.
3. They can be transpo:ted successfully by boat. Deck ta:tks with lids,
plenty of pU'Tlped seawater, and compressed air for aeration, are required.
- 14 -
4.
The smallest sable fish likely to be cultured cannot escape through
a net smaller than a 2-1/4 inch mesh (stretched measure) or through a pipe
smaller than 1-1/2 inch inner diameter.
5. Aeration, by compressed air through airstones, of the sea water in
tanks used for sablefish cUlture is essential during water supply failure
and desirable at all times.
6. The sea water supplied to the Nanairno Station fish culture facilities is considerably warmer during May to September than during the rest of
the year. At sunvner temperatures, fish weighing more than 4 pounds grow
less than 1/10 as fast as at winter temperatures and have higher mortalities.
Fish weighing less than 4 pounds are almost unaffected.
7. At winter temperatures, sablefish gain almost 1/3 pound per fish
per month and use about 5 pounds of food for every pound gained. Mortality
is slightly less than 1% per month.
8. Either (a) dogfish alone or (b) half and half dogfish and herring
or (c) "chicken-scrap" seems to be an adequate diet. Mussel is not suitable.
A ration based on Oregon pellet, although otherwise satisfactory, is probably
too expensive for corrmercial use.
9. A crowding rate of at least 9 pounds of fish per square foot of tank
bottom seems acceptable.
10. Recently noted unusually fast growth in cold water in a floating
pound indicates that the possibility of rearing sablefish within a net in a
protected. part of the open sea should be re-examined. Summer temperatures
of surface sea water would be a problem.
ACKNOWLEDGMENTS
The fish received excellent daily care from Messrs. R. M. Humphreys,
W. Griffioen and D. Pozar of the Station's Fish Culture Service. A. Kirkwood
devoted a good deal of time to making a superb set of branding irons. Mr.
W. P. McGee assisted ably with several special projects during the summer.
BIBLlCGRAPHY
Kennedy, W. A. and F. T. Pletcher. 1968.
Res. Bd. Canada, Tech. Rept. No. 74.
The 1964-65 Sablefish Study.
24 p.
Kennedy, W. A. 1969. Sab1efish Culture -- A Preliminary Report.
Bd. Canada, Tech. Rept. No. 107. 20 p.
Fish.
Fish. Res.
- 15 -
1970. Sablefish Culture -- Progress in 1969.
Canada, Tech. Rept. No. 189. 17 p.
Fish. Res. Bd.
1970. Juvenile Sablefish Cruises in 1970 Including Length, Weight,
Girth and Age Data. Fish. Res. Bd. Canada, MS Rept. No. 1119. 11 p.
Mighell, J. L.
Nitrogen.
1969. Rapid Cold Branding of Salmon and Trout with Liquid
J. Fish. Res. Bd. Canada, 26: 2765-2769.
Table 1- Some data on temperatures (Centigrade) of the seawater delivered to the fish culture
building, Nanaimo Station, during 1970.
MAXIMUM
TEMPERATURE
MINIMUM
TEMPERATURE
Number of days that the maximum temperature exceeded:
lDoe
HOC
12°C
13°C
14°C
15°C
16°C
17°C
Jan.
16 - Feb.
17
8.8
6.7
0
0
0
0
0
0
0
Feb.
18 - March 16
8.4
7.6
0
0
0
0
0
0
0
0
0
March 17 - Apr.
15
8.9
8.1
0
0
0
0
0
0
0
0
Apr.
16 - May
14
11.3
8.5
4
2
0
0
0
0
0
0
May
15 - June
16
15.2
8.7
31
26
15
8
5
2
0
June
17 - JUly
17
17.7
10.1
31
29
28
24
20
17
12
JUly
18 - AU9.
14
16.6
9.9
28
28
23
16
8
6
2
Aug.
15 - Sept. 15
17.5
10.3
31
30
29
22
17
10
8
3
26
25
15
2
0
0
0
0
0
Sept. 16 - Oct.
15
13.4
8.9
Oct.
16 - Nov.
16
9.8
8.0
4
2
0
0
0
0
0
0
Nov.
17 - Dec.
15
9.3
7.6
0
0
0
0
0
0
0
0
....
'"
Table 2. A sU;mlary of some of the resul ts of observations on the Batches of sablefish that
were kept at Nanaimo in 1970. "Warm water months" means mid May to mid September, "cold
water months" means the remainder of the year.
Diet
Continued beyond the end of 1970?
Nu:nber of months for which results
are reported
Average number of fish
BATCH 3
BATCH 6
BATCH 7
BATCH 8
Herring
Herring
Whole
Herring
+
+
Dressed
Dogfish
Various
Other
No
Ves
Dogfish
Ves
BATCH 9
Herring
+
+
Whole
Dogfish
Whole
Dogfish
Ves
Ves
7
12
12
12
25
29
32
31
195
....
~
Rate of gain in kilograms per fish
per month
- cold water months
- warm water months
Monthly Mortality Rate (Percenta3e)
- cold water months
- warm water months
Food to gain ratio (cold water
th
1) - weight of food
mon s on y - weight gained
0.13
0.13
0.13
0.13
Lost
0.10
0.02
0.02
0.04
0.8%
0.3%
1.7%
0.9%
6.ax
3.3%
3.9%
8.3%
5.0
6.0
4.5
4.8
0.14
5.1
Table 3. The effect of four rates of crowding on growth and iTlortality. Different rates of
crowding result from different amounts of fish in tanks of the same size as shown in the
first colwnn. Growth rates are given in kilograms per fish per month. Mortality rates
are given as percentages of fish alive at the beginning of a month that died during the
month.
Weight of
Fish per
Tank in
Kilograms
MORTALITY RATE
GROWTH RATE
Sept. Oct.
Oct. Nov.
Nov. Dec.
AVERAGE
Sept.
Oct.
Oct.
Nov.
Nov. Dec.
AVERAGE
10
0.14
0.21
0.13
0.17
a
a
0
~
20
0.16
0.27
0.11
0.18
4.~
5.3%
0
3.1%
30
0.18
0.16
0.18
0.17
a
a
3.7%
1.2%
40
0.20
0.21
0.12
0.18
a
4.4%
0
1.5%
....
00