Optimum Dietary Protein Level for Growth and Protein Efficiency without Hepatocyte Changes in Juvenile African Cichlids Pseudotropheus socolofi

Abstract

Six diets were formulated with protein levels ranging from 32.5% to 58.8% to determine the dietary protein level that would provide adequate growth and enhanced protein efficiency without pathological changes in the hepatocytes of juvenile ornamental African cichlids Pseudotropheus socolofi. Fish (0.11 g; 1.8 cm) were fed three times daily at 12% body weight per day for 10 weeks. Survival was greater than 95% for all treatments. At the end of the trial, fish on all diets had similar final lengths (P = 0.21). Final weight and final weight gain were significantly different among treatments (P = 0.04 and 0.03, respectively), and both variables exhibited a graded response. Final weight and weight gain increased as the protein level increased to 42.5% and then leveled off at protein levels greater than 42.5%. For fish on all diets, the final carcass protein composition was similar (P > 0.05) to the initial composition. Protein efficiency ratio and protein conversion efficiency decreased with an increase in dietary protein. The hepatosomatic index was not significantly different among diets (P > 0.05). There was a moderate amount of lipid storage in the liver irrespective of diet (40–59% lipid droplet area). Despite this, none of the diets produced liver pathologies. Based on broken-line analysis, the minimum level of dietary protein for optimum growth of P. socolofi to market size, under these experimental conditions and without significant pathological changes in the liver, was 40%.