Evaluation of the Optimum Dietary Selenium (Se) Level to Improve Immune Responses in Juvenile Olive Flounder, Paralichthys olivaceus

Abstract

This experiment was conducted to examine the utilization of added dietary selenium (Se) as an immune stimulant in juvenile olive flounder, Paralichthys olivaceus. Fish averaging <TEX>$4.0{\pm}0.1\;g$</TEX> (<TEX>$mean{\pm}SD$</TEX>) were fed one of seven semi-purified diets containing 0.56, 1.07, 2.86, 4.56, 43.15, 90.71, or 161.74 mg of Se/kg (<TEX>$Se_{0.56}$</TEX>, <TEX>$Se_{1.07}$</TEX>, <TEX>$Se_{2.86}$</TEX>, <TEX>$Se_{4.56}$</TEX>, <TEX>$Se_{43.2}$</TEX>, <TEX>$Se_{90.7}$</TEX> and <TEX>$Se_{161.7}$</TEX>, respectively) for 12 weeks, respectively. At the end of the feeding trial, the fish fed diets containing more than 43.2 mg of Se/kg showed above 90% mortality. There were no significant differences in weight gain, feed efficiency, specific growth rate, protein efficiency ratio, or hematological characteristics among the fish fed the <TEX>$Se_{0.56}$</TEX>, <TEX>$Se_{l.07}$</TEX>, <TEX>$Se_{2.86}$</TEX>, and <TEX>$Se_{4.56}$</TEX> diets. Se concentrations of the gill, kidney, muscle and liver tissues occurred in dose-dependent manners. Alternative complement pathway activation and the chemiluminescene responses of the fish fed the <TEX>$Se_{1.07}$</TEX> diet were significantly higher than those of the fish fed the other diets (P<0.05). These results indicate that the optimum dietary supplementation level of Selenium as selenoyeast could be 1.07 mg of Se/kg based on the non-specific immune responses of juvenile oilve flounder, Paralichthys olivaceus.