Abstract
A 45-day feeding trial was conducted to study the effect of replacing dietary fish meal (FM) with a tuna by-product meal (TBM) on the growth, feed efficiency, carcass composition and stress oxidative status of juvenile Nile tilapia, Oreochromis niloticus L.). Triplicate groups of fish (2.21 +/- 0.01g) were fed on four iso-nitrogenous and iso-energetic diets. The control diet (A(0)) used FM as the sole source of animal protein. In the other three diets (A(10)-A(30)), 33%-100% of FM was substituted by TBM at 10% increments. There were no significant differences (P>0.05) in growth performance among fish fed on diets A(0), A(10) and A(20). Fish fed these experimental diets (i.e., A(0), A(10) and A(20)) showed significantly (P<0.05) better daily mass gain, specific growth rate and protein efficiency ratio than those fed on diet A(30). Feed conversion ratio increased with increasing TBM content, but only the value found in fish fed on diet A(30) differed significantly (P<0.05) from the other treatments. The fish accumulated increasing quantities of lipids and decreasing levels of ash in their carcasses with increasing levels of dietary TBM. At the end of the experimental period, a significant increase (P<0.001) in catalase and glutathione S-transferase activities was seen only in groups fed on diet A30. Similarly, a significant enhancement in glutathione peroxidase and superoxide dismutase activities was observed in groups fed on diets A(20) and A(30) compared with the other groups. The results show that this product can be included up to 20% in practical Nile tilapia diets without any detrimental effects.