The optimum dietary protein level for the Mexican cichlid<i>Cichlasoma urophthalmus</i>(Günther): a comparison of estimates derived from experiments using fixed-rate feeding and satiation feeding

Abstract

Optimum dietary protein levels of young Cichlasoma urophthalmus (Günther) of 0.3 g mean weight were determined at 28°C using two methods, a fixed feeding rate of 6% body weight per day and satiation feeding. In the fixed rate trials nine isoenergetic diets were formulated with protein levels ranging from 347 to 561 g kg−1 using brown fish meal (anchovy) as the only protein source. In the satiation feeding trials, ten diets were formulated based on brown fish meal (mackerel) ranging from 0 to 450g kg−1 protein. When fish were fed a fixed rate diet, the best absolute growth was obtained with diets between 435 and 560 g kg−1 protein. Broken-line analysis showed that, in terms of weight gain (%), the optimum protein level was about 453 g kg−1. When fish were fed to satiation, the best absolute growth was obtained with the 383 g kg−1 protein diet, and broken-line analysis suggested an optimum of about 325 g kg−1. The difference between the two results, using the two techniques, is very marked. The probable mechanism underlying these data is discussed.