Comparison of purified and practical diets supplemented with or without beta-glucan and selenium on resistance of hybrid striped bass Morone chrysops female x M-saxatilis male to Streptococcus iniae infection
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This study was conducted to evaluate the efficacy of -glucan and selenium supplements to the diet on increasing survival of hybrid striped bass Morone chrysops X M. saxatilis exposed to Streptococcus iniae. A 2 2 2 factorial design was employed by including purified casein/gelatin-based diets and practical menhaden fish meal-based diets with supplements of either -glucan from barley at 0 and 0.1% of diet or sodium selenite at 0 or 0.2 mg/kg diet or a combination of these supplements. All diets were formulated to meet the nutritional needs of hybrid striped bass with the exception of selenium. The purified and practical basal diets contained 0.03 and 1.03 mg Se/kg, respectively, and the diets supplemented with sodium selenite had an additional 0.07 mg Se/kg on average. Juvenile hybrid striped bass initially averaging 2.44 0.17 g/fish were fed the eight experimental diets in triplicate 110-L recirculating aquaria for 6 wk, after which they were immersed in a bath of S. iniae at 6.2 106 CFU/mL for 2 h and monitored for 21 d. Weight gain and feed efficiency were significantly (P < 0.05) affected by diet type and selenium supplementation, with fish fed practical diets and those supplemented with selenium having the greatest values. Supplementation of -glucan to the purified or practical type diets did not significantly affect survival of fish after experimental infection. The most notable difference (P < 0.0001) was in the comparison of diet type; the survival rate of fish fed the practical diets was 75% compared to 35% for those fed the purified diets. Dietary supplementation of -glucan did not enhance disease resistance in the present study. Fish fed menhaden fish meal-based diets were significantly more resistant to S. iniae in comparison to the those fed the purified diets. Thus, nutritional influences on disease resistance of hybrid striped bass were evident in this study and warrant further investigation. by the World Aquaculture Society 2004.
