Almila Uysal, Kenan Engin
This study investigated the effects of combined dietary fish meal and oil replacement by soybean extract and increasing amount of plant oil mixture on growth performance, whole body and tissue amino acid and fatty acid compositions in Nile tilapia (Oreochromis niloticus). Diets in which 50% of the fish meal crude protein was replaced by soy bean extract along with 60, 80 and 100% of fish oil replacement by mixture of soy, canola and linseed oils (v/v, 1:1:1) were used in the study. Four iso-nitrogenous and iso-energetic experimental diets were prepared and fed to juvenile Nile tilapia (25 fish per tank with average wet weight of 16.24 Â± 0.66 g) twice in equal portions during morning (09:00-10:00 h) and afternoon (17:00-18:00) at a fixed rate of 4% BW.d-1 for 84 days. At the end of 84 day grow out period growth parameters and whole body and muscle tissue amino acid and fatty acid compositions were assessed. Fish in each dietary treatment more than doubled its initial average weight and no statistical differences (P>0.05) were found among dietary treatments in terms of measured growth parameters. It was also demonstrated that diets supplemented with soy bean extract and increasing amount of plant oil mixture proportionally increased the crude protein contents and significantly decreased (P<0.05) the crude ash levels in fish whole body samples compared to that of fish fed fish meal and oil control diet. It appeared that except for one or two amino acids, fish fed diets supplemented with soy bean extract and increasing amount of plant oil mixture tended to increase the muscle tissue essential and non-essential amino acid levels and that L-lysine and DL-methionine used in these diets were effectively used for growth in juvenile Nile tilapia. Except for several fatty acid classes, fish whole body and tissue fatty acid compositions generally mimicked the feed fatty acids following the growth trial. It was also understood that DHA was probably deposited whereas EPA was used for energy production in fish fed diets supplemented with soybean extract and increasing amount of plant oil mixture. Furthermore, fish fed diets supplemented with soy bean extracts and plant oil mixtures had significantly higher (P<0.05) intermediate metabolites like 18:3n-6 and 20:3n-6 of the n-6 LC HUFA biosynthesis in whole body and tissue samples compared to that of fish fed the control diet implying Nile tilapia in this conditions might have activated the Î5 and Î6 elongation and desaturation enzymes. It was demonstrated that the partial replacement of dietary fish meal and 100% replacement of dietary added fish oil by soy bean extract and plant oil mixture did not compromise growth rates or drastically change whole body and tissue amino acid and fatty acid compositions in juvenile Nile tilapia.