Effects of dietary soybean oil inclusion to replace fish oil on growth, muscle fatty acid composition, and immune responses of juvenile darkbarbel catfish, Pelteobagrus vachelli

An 80 day feeding trial was conducted to evaluate the effects of dietary inclusion of soybean oil to replace fish oil in the diet on growth, muscle fatty acids and immune responses of Pelteobagrus vachelli. Isonitrogenous and isocaloric diets were formulated with four fish oil to soybean oil ratios at 8:0 (FO, control), 6:2 (MO1), 2:6(MO2) and 0:8 (SO) in triplicate. Each diet was fed to juvenile darkbarbel catfish (1.0 ± 0.02 g) twice daily. No significant differences were found in weight gain, special growth rate, hepatosomatic index and intraperitoneal fat ratio among all the treatments. Incorporation of soybean oil significantly modified the fatty acid composition and n-3 and n-6 PUFAs ratio in muscle of fish. Fish fed MO1 showed significantly higher serum lysozyme activity, complement C3 and C4 contents and total IgM content than those fed other diets. These results indicate that partial replacement of fish oil with soybean oil does not compromise fish growth, but improve fish immunity. This study suggests that 25% fish oil replacement with soybean oil can be used in the practical diet of this fish.   Key words: Darkbarbel catfish, Pelteobagrus vachelli, soybean oil, growth, fatty acid composition, immune responses.