EVIDENCE FOR COMPENSATORY GROWTH AND ITS UTILITY IN THE CULTURE OF HETEROBRANCHUS-LONGIFILIS

Three trophic levels were tested with the African catfish Heterobranch us longifilis. In the Ist trial, fish with a mean weight of 60 g (12 b atches of 8 fish), were subjected to severely restricted feeding (1% o f body weight) for three weeks, then increased rations for three weeks either to ad libitum feeding or to 3% of body weight. Growth sates we re compared to those of fish that had been continuously fed either ad libitum or at 3% of body weight. Although the final live weights of fi sh on restricted diets were lower than those of fish on unrestricted d iets, the results indicate that a restrictive feeding rate ultimately induces a significantly higher specific growth rate, and a better food conversion ratio. This compensatory growth is caused both by hyperpha gy and by an improved metabolism. A positive effect of hyperphagy was still noted during the following two weeks. During the 2nd experiment, silurids of an initial mean weight of 141 g (6 batches of 18 fish) we re fed for 10 weeks either at a constant rate of 4% body weight, or fe d alternately on a diet restricted to 2% of body weight for one week t hen increased to 4 or 5% of body weight for the next week. At the end of the trial (19 weeks), mean weights were not significantly different . The best food conversion ratio (1.8) was found among the fish on res tricted diets alternated with increased rations equal to that of the c ontrol (4%). In the 3rd experiment, silurids of a mean weight of 340 g (6 batches of 16 fishes) were fed for five months at a constant rate of 3% of body weight and those of fish fed alternately at 2% then 4% u sing 15-day intervals following lunar cycles were compared. At the end of the experiment, final mean weights varied from 977 to 1127 g, whil e the food conversion ratios varied from 2.1 to 2.5. The best performa nces, considering all criteria, were those of group of fish fed restri cted diets of 2% of body weight during the waning moon and then increa sed to 4% during the waxing moon. Conversely, the worst results were o btained with those fish on a restricted diet during the waxing moon. T o fully utilize the phenomenon of compensatory gain as illustrated in the silurid, dietary restriction, even a mild one for a one week perio d can be recommended. However, there appears to be very little profit in attempting to benefit from hyperphagy after restricted diets for tw o weeks.