Evaluation of poultry by-product meal in commercial diets for juvenile cobia ( Rachycentron canadum)

Abstract

A 10-week feeding trial was conducted to evaluate the potential use of poultry by-product meal (PBM) as a partial replacement of fish meal protein in the commercial diets for juvenile cobia. Five isonitrogenous (approximately 45%) and isolipidic (about 11%) diets were formulated to contain graded levels of PBM, and fish meal protein was replaced with a pet food-grade PBM at 15, 30, 45, 60% level (PBM15, PBM30, PBM45, PBM60, respectively) without lysine and methionine supplementation. The reference diet (PBM0) contained fish meal and soybean meal as protein sources. Each diet was fed to groups of 20 juvenile cobia initially averaging approximately 5.8 g in triplicate 500-l tanks twice daily to apparent satiation. The results showed that growth performance and survival for fish fed PBM-supplemented diets were not significantly lower compared to fish fed the reference diet ( P > 0.05). However, protein efficiency ratio and feed efficiency ratio were significantly affected by the replacement level of fish meal protein with PBM, fish fed the PBM30 and PBM45 diets had higher PER and FER than fish fed the reference diet and the other diets. The condition factor, viscerosomatic index and intraperitoneal fat ratio were not significantly affected by the dietary treatments, however, fish fed the PBM45 diet had a higher hepatosomatic index than fish fed the other diets. There were no significant differences in moisture, crude lipid, ash, calcium and phosphorus content in whole body among all treatments, but the fish fed the reference diet had higher crude protein in whole body than fish fed the PBM-supplemented diets. There were no differences in liver superoxide dismutase, catalase, glutathione S-transferase and glutathione peroxidases activities among fish fed the experimental diets. Hematocrit, hemoglobin, red blood cell and total immunoglobulin were not significantly affected by the replacement level of fish meal protein with PBM. With the exception of plasma glucose content, there were no significant differences in plasma triglyceride, cholesterol and total protein concentration in fish fed the experimental diets. The results of this study indicated that good quality terrestrial PBM can successfully replace fish meal in the commercial diets for cobia, and the optimal level of fish meal replacement with PBM was determined by quadratic regression analysis to be 30.75% on the basis of maximum protein efficiency ratio.