Effects of replacement of dietary fish oil by soybean oil on growth performance and liver biochemical composition in juvenile black seabream, Acanthopagrus schlegeli

A 9-week feeding experiment was carried out on juvenile black seabream Acanthopagrus schlegeli to evaluate the effects of dietary replacement of fish oil by soybean oil on fish growth and liver biochemical composition. Fish in triplicate were fed four diets, in which 0% (FO as control), 60% (60SO), 80% (80SO) and 100% (100SO) of fish oil was replaced by soybean oil. The weight gain of fish fed 60SO or 80SO diet was similar to that of fish fed the control diet, but a total replacement of fish oil by soybean oil significantly reduced fish growth. Although the inclusion of soybean oil resulted in an increase in the crude lipid content of the liver, the level of fish oil replacement did not significantly alter the hepatosomatic index, feed conversion ratio, condition factor and liver proximate composition. The inclusion of soybean oil in seabream diets increased hepatic α-tocopherol concentrations, but reduced thiobarbituric acid-reactive substances and plasma cholesterol. Linoleic acid and linolenic acid significantly increased in fish fed soybean oil diets, but docosahexaenoic acid, eicosapentaenoic acid and the ratio n - 3/n - 6 were significantly reduced by the inclusion of dietary soybean oil (P < 0.05). Our results indicated that the inclusion of soybean oil increased the hepatic α-tocopherol content and reduced lipid peroxidation in fish. However, complete substitution of fish oil with soybean oil reduced growth efficiency. Thus, 60-80% replacement of fish oil by soybean oil is recommended in diet formulation for black seabream.