- One means of evaluating the temperature requirements of an
animal is to determine changes temperature causes in the uses and
losses of energy and materials in the food the animal consumes. To
develop energy budgets for cichlids (Cichlasoma bimaculatum) at different
temperatures (20, 24, 28, 32 and 36 C) data were obtained on
food intake, growth (total, fat, and protein), fecal losses, maintenance
requirements, and other uses and losses of energy and materials
including specific dynamic action, activity, and nitrogen excretion.
Starvation experiments were conducted to provide information
on the metabolic cost of existence and on adjustments in body composition
in the absence of food. Energy expenditure during starvation,
estimated from heat of combustion data, was found to increase
linearly with temperature over 4, 13 and 20 days of starvation.
The caloric cost of existence per fish per day was greatest
during the first four days at all temperatures and decreased as starvation was prolonged to 20 days. Caloric losses, and dry weight
losses showed essentially the same thing. Protein catabolism increased
regularly with temperature and decreased slightly with
duration of starvation. Fat catabolism did not vary significantly with
temperature but decreased markedly as starvation was prolonged.
Food intake, growth, and food conversion efficiency varied
greatly with changes in temperature. Cichlids were fed ad libitum
on small aquatic worms of the genus Tubifex. For food consumption
as well as growth, the optimum temperature dropped from 32 to 28
to 24 C as the experimental period was extended from 5 to 12 to 19
days. Optimum growth in dry weight and calories occurred at the
same temperatures. Growth of cichlids through time at 20 and 28 C
was nearly linear; at 24 C the curve was exponential. At 32 and 36
C, the growth curves rose and then declined. When the fish were
held separately during the experiment, food conversion efficiency of
cichlids was highest at 20 C and decreased with increasing temperature.
Efficiencies decreased with duration of the experiment. When
fish were held in groups during the experiment, efficiency was low
at both high and low temperatures.
The guts of the cichlids were found to contain food up to 30
hours after an ad libitum meal at all temperatures. They were reasonably
empty after 36 hours. Thus, no significant correlation was
found between temperature and the length of time necessary for the guts to empty. Food material not absorbed was measured by wet
combustion. Percentages of absorption of unrestricted rations were
found to be 83, 84, 88, 85 and 69 at 20, 24, 28, 32 and 36 C. Percentages
of food absorption were much higher on the restricted
ration than on the unrestricted ration. Absorption appears to have
been optimal at 28 C.
Specific dynamic action (SDA) was estimated at different
temperatures by taking the difference between oxygen consumption
of unfed and fed cichlids at the same levels of activity. SDA represented
22, 20, 19, 33 and 33 percent of the food consumed at 20, 24,
28, 32 and 36 C, when the fish were swimming at 4 cm/second.
SDA was generally complete within 36 hours after feeding.
Graphs showing energy and material intake, utilization, loss,
and scope for growth at each temperature during different experimental
periods were developed both in terms of calories per fish
per day and calories per gram of fish per day. The evidence suggests
that the optimum temperature for growth of this cichlid is
near 24 C.