Inclusion of soybean meal in tilapia ( Oreochromis niloticus × O. aureus) diets at two protein levels

Abstract

A feeding trial was conducted with tilapia ( Oreochromis niloticus × O. aureus) to determine whether commercial hexane-extracted soybean meal could be used as a partial replacement for fish meal at two dietary protein levels, 24% and 32%. At each protein level, 30% of fish meal protein was replaced by soybean meal with and without methionine supplementation. Fish meal was used as control. The experiment was carried out for 2 months in a recirculated rearing system. For soybean meal, without methionine supplementation, in diets containing 32% protein, growth and feed conversion were reduced significantly ( P < 0.05) as compared to the control diet. However, the difference between the test and control groups was not significant ( P > 0.05) when the diets contained 24% protein. With methionine supplementation, the differences between the test and control groups were not significant ( P>0.05) for either protein level in the diet. Protein digestibility, dry matter digestibility, and protease activity in the stomach, intestine and liver of tilapia fed the fish meal control diet were identical to those noted in fish receiving the test diet, regardless of dietary protein content. These data suggest that without methionine supplementation, fish meal can be replaced partially by commercial hexane-extracted soybean meal when the dietary protein level is suboptimal for tilapia growth. However, at the optimal dietary protein level (32%), partial replacement of fish meal protein with protein from soybean meal depresses both growth and feed conversion in tilapia.