ARIZONA GAME AND FISH DEPARTMENT
GROSS PRIMARY PRODUCTIVITY-CONSUMER RATIOS
William J. McConnell
Partial Completion Report
December 1, 1959 December 31, 1961
Project F- 8-R- l&Z
Job E
Abstract
Production of fish and amphibian larvae was compared to gross photosynthesis (gross primary productivity) in 95 gallon microcosms. All food
consumed by the test animals resulted from photosynthesis within the tanks e
except for some minor accidental exceptions. Biomass increase of the more
carnivorous consumers equaled about 0.93 percent of gross photosynthesis,
a figure which compares closely with the same ratio for Pena Blanca of 0.98
percent. Production of biomass of the mostly herbivorous Tilapia averaged
10 percent of gross photosynthesis.
Recommendations
Relatively simple and direct measurements of aquatic gross photosynthesis appear to be the best criterion of productivity available for classifying
fisheries with regard to potential. Exact interpretation in terms of fish production is not possible; however, useful approximations may be made. Im-:
provements in interpretation may be expected to result from continued investigation of the relation of fish production to gross photosynthesis.
Objective
To gain information on the ratio of game fish production to gross photosynthesis (gross primary productivity).
Methods
Fish and clawed frog tadpoles were reared in a series of eight microcosms during 1961 wherin all food was provided by algal photosynthesis within
the microcosms. Minor unintentional additions of food occurred when introduced consumers died in some microcosms and decomposed or were consumed
by snails. When consumer organisms died, other kinds were introduced until
a thriving population was eventually established (Table I). Fish used were Gila
topminnows, Pc ciliopsis occidentalis ( Baird and Girard); medakas, Otvzias
Iatipes (Schlegal); Tilapia mossambica (Peters); and the common mullet, MULL
Cephalus (Linnaeus). The clawed frogs were the African species Xenopus laevis
(Daudin). Snails Physa sp. and unidentified clams from an irrigation ditch in
Yuma were also introduced but these died before the end of the experiment. Gila
topminnow populations were established in three microcosms when three newborn young developed into two males and a female in each tank and reproduced
within 70 days after introduction. 'The young introduced in the fourth tank all
developed into males and meda,ka fry were substituted for reproduction by Gila
topminnows. The Tilapia suffered no mortality after introduction on July 16 in
tanks 5, 7 and 8. Those introduced into tank 6 died for some unexplained reason
and that experiment was terminated.
This report covers that portion of the data collected under Job E which has not
been reported in a previous publication (McConnell 1962).
*
TABLE I. Dry Biomass and Numbers of Consumers Added to Microcosms 1 through 4.
TANK 1
TANK 2
Weight
(Gros.) No. Animal
No. Animal
(Ntitrients added to all tanks. ) •
Date
Mar. 1
Weight
(Gms.)
TANK 3
No. Animal
_
TANK 4
Weight
(Gms:) - No. _ Animal
--,
0.050 4 Snails
0.050
Weight
(Gins.)
4 Snails
0. 050
7 Tadpoles
0. 002
Mar. 17 4 Snails
0. 100 4 Snails
Mar. 24 4 Snails
0. 100
Mar. 24 3 Tadpoles
0.001 8 Tadpoles
0.003 5 Tadpoles
0.002
Mar. 29 9 Clams
0. 106 9 Clams
0. 099 8 Clams
0. 091 7 Clams
0.
00891
0. 0
fil
m
ots
May 23 3 Gila topminnow 0. 009 3 Gila topminnow 0.009 3 Gila topminnow 0. 009 3 Gila topminnow
1"
2 Mullet
July 17
0. 775
Aug. 11
25 Threadfin shad 0.023
Aug. 18
81 Medakas
co
0.023
All months
0.266
0.451
1.020
0504
Decomposed in
Microcosms
0.257
0.442
0.493
0.320
jiOne
of these weighing 282 gms. when stocked died and decomposed in the tank.
Microcosms were established in 95 gallon stock tanks which were painted
with "Tygon" brand non-toxic laboratory paint. The tanks were placed where
direct sunlight would fall on them most of the day; this made cooling systems
necessary. Cooling was provided by placing each 95 gallon tank within a 105
gallon tank and flowing well water through the space
between
them. Tempera0
0
tures were restricted to an extreme range of 75 to 85 F. from May through
September. Similar experiments attempted in 1960 failed because no cooling
system had been worked out and they were kept in the shade.
Transparent "Mylar" covers were provided to exclude dust, rain, etc.
Gentle water circulation was caused with minimal aeration. Carbon dioxide
content of the air picked up by the aerator pump was increased by allowing dry
ice to sublimate slowly near the intake. Rate of sublimation was controlled by
degree of insulation, increases or decreases being made according to the pH
trends in the tanks.
Experiments were begun and sustained by adding nitrogen and phosphorus to tapwater at monthly application rates equal to 50 and 10 pounds per acre
respectively of each element. Algae were seeded by adding water from several
natural habitats including Pena Blanca Lake.
Productivity was measured as oxygen produced during gross algal photosynthesis. Methods and theory involved are explained in two publications based
on work under this project (McConnell, 1962; McConnell, 1963).
Findings and Discussion
Validity of Experiments:
The microcosms were intended to be self sufficient with regard to organic matter. All foods were to be produced through photosynthesis in the
communities with the exception of the biomass of the consumers added. Allowable, nonorganic additions were limited to necessary biogenic salts, carbon
dioxide and sunlight. This original plan was departed from to the extent that
the death of consumers added food. This only occurred in tanks 1 through 4.
Snails and clams added originally as herbivores died and decomposed with their
shells. By May, when the Gila topminnows were introduced, no organic animal
remains were present. A mullet in tank #3 died and decomposed during the
first week of August before the medaka fry were added (Table I). It is possible
in this case that the protozoan population was increased by the decomposition
of the mullet. Such indirect entry of organically bound energy into the food
chain of the medakas could not be reflected in any noticeable biomass increase.
The release of N and P by decomposition of organic matter would stimulate
photosynthesis but this would be accounted for and would not constitute an
addition of food.
Trophic Position of Consumers:
Mullet and Xenopus tadpoles are both feeders on finely divided organic
sediments. Although not direct predators they are carnivorous to the extent
that the sediment contained animal material. In the microcosms most of the
sediment was composed of feces or living and dead algae. A small increment
was composed of protozoans. Both mullet and Xenopus were, therefore, mostly
herbivorous. Both Gila topminnows and medakas prefer animal matter but
apparently can subsist on algae. They are probably somewhat more omnivorous
F8R1&2- JE
3
THAN ANY OF THE centrarchids OR TROUT AND THEREFORE CLOSER TO THE BASE OF THE
Tilapia IN THE MICROCOSMS APPARENTLY LIVED ON A DIET OF UNICELFOOD WEB.
LULAR AND AUFWUCHS FORMS OF ALGAE.
FINAL POPULATIONS:
ALL MICROCOSMS SUPPORTED POPULATIONS SO CROWDED THAT LITTLE GROWTH
WAS OCCURRING AT THE END OF THE EXPERIMENT. THE FEMALE GILA topminnows
WEIGHED ABOUT 0.02 GRAMS EACH WHEN INTRODUCED IN LATE MAY AND OVER 1.5 GRAMS
EACH 70 DAYS LATER. YOUNG BORN TO THE FEMALES IN THE MICROCOSMS AVERAGED
LESS THAN O. 1 GRAM LIVE WEIGHT 70 DAYS AFTER BIRTH BECAUSE OF FACTORS RELATED
TO CROWDING. THE Tilapia WERE ALSO MUCH MORE CROWDED THAN THEY WOULD PROBABLY BE IN ACTUAL FISHERIES.
20
THE HIGHEST trophic EFFICIENCY WAS REALIZED IN THE Tilapia TANK UNDER
PERCENT HARVEST PER WEEK FOR THE LATTER HALF OF THE EXPERIMENT (TABLE II).
PRODUCER ORGANISMS:
1 THROUGH 4 DEVELOPED LARGE MATS OF FILAMENTOUS ALGAE AND INTERCOMMUNITIES. THOSE WITH AN EFFECTIVE HERBIVORE ( Tilapia)
phytoplankton
MITTENT
COMMUNITY AND DEVELOPED ONLY A SMALL AMOUNT
photoplankton
DEVELOPED A DENSE
OF ATTACHED OR FILAMENTOUS ALGAE. THE ORGANIC RESIDUE IN TANKS 1 THROUGH 4 WAS
THREE TO FOUR TIMES GREATER THAN IN 5, 7 AND 8 IN WHICH THE Tilapia WERE THE
TANKS
PRINCIPAL CONSUMERS (TABLE II).
PRODUCTION RATIOS:
HARVESTS OF THE MOST PREDACEOUS VERTEBRATES, GILA topminnows AND
medakas, EQUALED BETWEEN 0.69 AND 1.26 PERCENT OF GROSS PHOTOSYNTHESIS WHEN
LIVE WEIGHTS ARE USED. THE ANGLER HARVEST OF LARGEMOUTH BASS AND BLACK CRAPPIE
FROM PENA BLANCA LAKE WAS EQUAL TO 0.98 PERCENT OF GROSS PHOTOSYNTHESIS
( MCCONNELL, 1963). CONSIDERING THAT THE centrarchids FROM PENA BLANCA LAKE
WERE PROBABLY MORE PREDACEOUS THAN THE GILA topminnows OR medakas AND THAT
TOTAL PRODUCTION INCLUDING nonangling MORTALITY WAS ACCOUNTED FOR IN THE TANKS,
PENA BLANCA LAKE FIGURE APPEARS SOMEWHAT HIGH. ASIDE FROM ERRORS THE EXPLANATION FOR THE HIGHER PENA BLANCA FIGURE MAY LIE IN THE LARGE QUANTITY OF allochthonous
ORGANIC MATERIAL WHICH ENTERED THE LAKE VIA FLASH FLOODS.
THE PROGRESSIVE HARVESTS DURING THE EXPERIMENT IN TANKS 2 AND 4 DID NOT
CONSISTENTLY INCREASE THE TOTAL HARVEST. THEORETICALLY, IT WOULD BE EXPECTED THAT
IN AN OVERCROWDED POPULATION REMOVALS WOULD ALWAYS BE REFLECTED IN AN INCREASED
GROWTH RATE OF THOSE FISH REMAINING. THIS OCCURRED IN TANK #2 (50 PERCENT HARVEST/WEEK) WHERE THE LAST GILA topminnows HARVESTED HAD REACHED A TOTAL LENGTH
OF 26-27 mm. IN TANK #4, UNDER 20 PERCENT WEEKLY HARVEST, THE LAST GILA TOPMINNOWS HARVESTED ONLY ATTAINED A LENGTH OF 21-22 mm, WHEREAS THOSE IN TANK #1
( UNHARVESTED) WERE 23-24 mm IN TOTAL LENGTH. THE LARGEST medakas IN TANK #3
ATTAINED TOTAL LENGTHS OF 26-27 mm WITHOUT HARVEST AND UNDER A POPULATION DENSITY
COMPARABLE TO THAT OF THE GILA topminnows IN TANK #1. THE Tilapia HARVESTS REFLECT THE GREATER trophic EFFICIENCY OF A HERBIVORE OVER AN OMNIVORE (TABLES II AND
III). THERE ARE PROBABLY NO NATIVE GAME FISHES WHICH ACHIEVE AN EFFICIENCY OF CONVERSION OF GROSS PHOTOSYNTHESIS OF 10 PERCENT AS Tilapia DID IN THESE EXPERIMENTS.
CONVERSION OF ACTUAL NET PRODUCTION WOULD HAVE TO BE CLOSE TO 20 PERCENT. NO
ACCEPTABLE NORTH AMERICAN SPORT FISH IS HERBIVOROUS TO THIS DEGREE, AND THE POPULATION DENSITIES USED IN THE MICROCOSMS EXCEED ANY THAT WOULD PRODUCE A SUFFICIENTLY RAPID INDIVIDUAL GROWTH RATE. IT PROBABLY IS SAFE TO CONCLUDE THAT NATIVE GAME
F8R1&2- JE
4
TABLE II.
Productivities of Microcosms as Numbers and/or Dry Weight in Grams (except where noted otherwise).
11
Tank #1
Tank #211Tank #3
Tank #4
Tank#5
Tank #7
No. Wt. No. Wt. No. Wt. No. Wt. No. Wt. No. Wt.
Organism
/
-
-
-
-
1
0 , 52
1
0. 18
-
-
75
1. 13
71
0.92
3
0. 16
84
0.69
-
-
Medaka
80
0. 72
Xenopus
4
0. 55
Mullet
Gila topminnow
Tilapia
Total vertebrates
-
Tank #811
No, Wt.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
15
3. 58
10
5. 62
25
5. 09
75
1. 13
71
0.92
88
1.95
85
0.87
15
3.58
10
5.62
25
5.09
fil
in
i
CV
GZ
Total additional
organic material
1
Gros s photosynthesis
(as gms oxygen)
II
148
151
105
151
29
38
24
461
520
512
499
276
311
226
,--1
P4
oo
fr-f
A progressive harvest program was started about 30 days after reproduction by Gila topminnows (or introduction
of Tilapia fry). In tanks 4 and 8, 20 percent of the remaining number was removed weekly; in tank #2, 50 percent
was removed weekly.
I/ Initially two mullet fingerlings (2") were placed in each tank as consumers; however, all but two leaped out during
attempted recapture shortly after their introduction. Injuries sustained made it unwise to return them. Slight
weight losses occurred among all mullet in the early part of the experiments. Therefore, no production was lost.
-3-/ Includes algae, bacteria, small invertebrates, detritus and feces.
En
TABLE III. Production Data and Ratios for Microcosms.
Tank #1
Experiment duration (days)
Gross photosynthesis as
pounds 0 2 /acre
Vertebrate harvest as live
weight in pounds/acre
Vertebrate harvest as per
cent of gross photosynthesis
Harvest of medakas and Gila
topminnows as live weight in
pounds/acre
Harvest of medakas and Gila
topminnows as percent of
gross photosynthesis
Tank #2
Tank #3
Tank #4
Tank #5
Tank #7
Tank #8
208
208
208
208
154
154
154
6760
7630
7520
7310
4050
4560
3330
85
69
144
65
294
461
419
[7.1
1-)
i
NI
1.26
85
1.26
0.90
69
0.90
1.92
65
0.88
0.89
51
0.69
7.27
9.90
12.70
60 so
.
c:4
c
rfi
fish production equal to two percent of gross photosynthesis is highly satisfactory
while that falling below 0.5 percent of gross photosynthesis indicates a weak point
in the trophic system.
Literature Cited
McConnell, Wm. J. , 1962. Productivity relations in carboy microcosms.
Limnol. and Oceanogr. , 7:335-343.
McConnell, Wm. J., 1963. Primary productivity and fish harvest in a small
desert impoundment. Trans. Am. Fish. Soc. , 92:1-12.
Prepared by: William J. McConnell
Project Leader
Approved by:
J. Smith, Director
(
R. J. i
ruenewald,
Coordinator
F8R1&2- JE
7