DIETARY INDOLE-3-PROPIONIC ACID ON THE GROWTH PERFORMANCE AND INTESTINAL HEALTH OF LARGE YELLOW CROAKER (LARIMICHTHYS CROCEA) LARVAE

To investigate the effects of dietary isophorone (IPA) on the growth performance and intestinal health of large yellow croaker (Larimichthys crocea) larvae, a 30d feeding trial was conducted. Larvae with an initial mean weight of (4.98±0.07) mg were selected as research subjects and fed micro-diets supplemented with IPA at levels of 0, 0.005%, 0.010%, and 0.020%. Regarding survival and growth performance, supplementation with 0.005% and 0.010% IPA significantly enhanced the survival rate, specific growth rate, final body length, and final body weight compared with the control group. In terms of intestinal development, a significant increase in intestinal fold height was observed in the 0.005% and 0.010% IPA groups relative to the control. Concurrently, dietary supplementation of 0.005% IPA significantly increased intestinalbrush border lactase activity; meanwhile, addition of 0.010% and 0.020% IPA significantly enhanced brush border leucine aminopeptidase activity, whereby promoting intestinal development. In terms of genes related to intestinal development, the mRNA expression levels of pcna, odc, cateninα1, zo-1, zo-2, claudin1, claudin5, and occludin were significantly upregulated by 0.005% IPA compared with the control. In terms of digestive capacity, the activities of intestinal amylase, lipase, and trypsin were significantly improved by 0.005% IPA. Regarding absorptive capacity as reflected by brush border enzyme activities, the activity of intestinal Na⁺/K⁺-ATPase was significantly increased by the 0.005% IPA treatment. In terms of digesting and absorbing related genes, the mRNA expression levels of pept1, slc7a7, slc7a5, slc6a6, slc7a1a, and slc36a1 were significantly upregulated by the 0.005% IPA level; meanwhile, the mRNA expression levels of cck, pept1, slc6a6, and slc36a1 were significantly upregulated by the 0.010% IPA level, thereby enhancing the digestive and absorptive capacities of the larvae. That the growth performance of L. crocea larvae could be significantly enhanced by dietary IPA supplementation was demonstrated in this study. Consistent with the comprehensive analysis of all parameters, the optimal addition level of IPA was suggested to be 0.005%—0.010%.