Table 6. Theoretical growth (AB) equations to describe the growth potential of young
Tilapia rendalli at various temperatures. AB is expressed in joules per day, C is the energy
(J) of food consumed per day and M the fresh mass of the fish, weighing between 40 and
60 g.
Table 7. A comparison of the energy required for satiation in the laboratory (see Table 2)
and the estimated energy required for maintenance as derived from Table 6 when AB = 0,
for Tilapia rendalli feeding on Ceratophyllum demersum.
Maintenance energy
Temperature Laboratory s tiation
B
require ent
OC (kJ d- ) (kJd-? )constant temperature but are usually subjected to varying degrees of daily
thermal fluctuations. If fry (10 g) restricted in aquaria, were subjected to a
thermal oscillation (18°C night, 30°C day), then their growth rate was found
to be very similar to that shown by a control group of fry maintained at
30°C. The major difference between the two groups was found, however, in
their feeding, with those fry maintained at a constant temperature of 30°C
consuming up to twice as much food as those fry subjected to daily temper-
ature changes. Both groups of fry grew from a mean standard length of
about 6.5 cm to a maximum of 10 cm over a 45 day period. This growth
represents an increase from 10 g to about 40 g in mass. Although the two
groups showed very similar growth, their food intake was very different. An
explanation for this difference can be obtained using the growth equations
of Table 6. For example, a 50 g fish maintained at a constant temperature of
30°C and having a growth rate of 1,000 J/d (196 mg fresh mass per day)
would be expected to consume: