Effects of dietary supplementation of glycyrrhizic acid on growth performance, survival, innate immune response and parasite resistance in juvenile large yellow croaker, Larimichthys crocea (Richardson).

An 8-week feeding experiment was conducted to investigate the effects of dietary glycyrrhizic acid ( GA) on growth, survival and immune response of juvenile large yellow croaker, in seawater floating net cages. GA was supplemented into the basal diet to formulate four isonitrogenous and isoenergetic practical diets containing 0.00% (the control diet), 0.01%, 0.02% and 0.04% GA of dry weight, respectively. Triplicate groups of 60 fish were fed to apparent satiation by hand twice daily. The results showed that the specific growth rate, survival rate and feed efficiency ratio revealed no significant differences among dietary treatments ( P > 0.05). The phagocytic index of head kidney macrophage was significantly increased by the supplementation of 0.04% dietary GA compared to the control group ( P < 0.05). Fish fed 0.04% dietary GA also showed significantly higher serum lysozyme activity than fish fed the control diet and diet with 0.01% GA ( P < 0.05). The cumulative mortality rate after natural infestation of parasites (protozoan, Cryptocaryon irritans Brown) showed no significant differences among dietary treatments. These results suggested that dietary glycyrrhizic acid improved certain non-specific immunological parameters of juvenile large yellow croaker. However, GA was not able to protect juvenile large yellow croaker effectively from protozoan infection. [ABSTRACT FROM AUTHOR]