Effects of indole-3-butyric acid supplementation in diets containing high soybean meal on growth, intestinal inflammation, and intestinal flora of pearl gentian grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatu♂)

Abstract

Soybean meal and its processing products have been widely used in fish feeds. In aquaculture, there is a lack of effective targeted protection against food-borne enteritis caused by feeding soybean meal. Our preliminary research found that Indole-3-butyric acid (IBA) has the potential application value. The present research evaluated the influence of supplementing different levels of IBA to diets containing high soybean meal on alleviating intestinal inflammation in juvenile pearl gentian grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂). The feeding experiment lasted for eight weeks. The FM diet with fish meal as the main protein source was prepared. In addition, six diets were prepared in which soybean meal was used to replace some of the fish meal as a secondary protein source. IBA was added to these six diets at 0 g/kg, 0.8 g/kg, 1.6 g/kg, 2.4 g/kg, 3.2 g/kg, and 4.0 g/kg, respectively. The use of soybean meal to replace some of the fish meal in the diet resulted in weakened growth performance of the fish. Growth inhibition due to SBM ingestion was significantly reduced in fish fed diet supplemented with 2.4 g/kg IBA. Feeding the SBM diets caused a severe inflammatory reaction in the distal intestine of the fish, and IBA helped to suppress the inflammation, as evidenced by changes in histological characteristics, immune-related biochemical index levels, and immune-related gene expression levels between the groups. In addition, this study investigated the role of IBA feeding on fish from the perspective of intestinal flora. IBA interacts with the intestinal flora, leaving the intestinal flora of fish with enteritis in a recovering state. These findings provide a theoretical basis for IBA to mitigate SBMIE in pearl gentian grouper and promote the further application of soybean meal in carnivorous fish.