Growth, feed utilization and body composition of black catfish, Rhamdia quelen, fry fed diets containing different protein and energy levels

Abstract

In order to evaluate the protein and energy requirement of black catfish fry, eight experimental diets containing four protein levels (30%, 34%, 38% and 43%) and two lipid levels (8% and 14%) were tested. For 30 days, 0.3 g fish were fed the experimental diets to approximate satiation, twice a day. Growth was significantly affected by both protein and lipid content of the diets. At the same protein level, final mean weight, weight gain and specific growth rate (% per day) were significantly improved ( P<0.01) by increasing the dietary lipid (energy) content. At the same dietary lipid content, final weight, weight gain and SGR obtained with diets containing 38% and 43% protein were similar and significantly ( P<0.01) higher than those obtained with diets containing 30% and 34% protein. Feed conversion ratio was improved by increasing the dietary protein content, obtaining a value of 0.95 (fed/gain) with diets 38/14 and 43/14. Protein efficiency ratio (PER) was not significantly affected by the different dietary treatments for each dietary lipid or protein level tested, reaching a mean value of 2.80 in fish fed high lipid diets. Results obtained in the present study suggest that for black catfish fry, the optimum dietary protein content is 37% with an estimated optimum digestible protein (DP)/DE ratio of 23.6 mg kJ −1.