Comparative effects of different dietary pectin types on growth performance and intestinal health in pearl gentian grouper ( Epinephelus fuscoguttatus♀ x E. lanceolatus♂)

Pectin, a non-starch polysaccharide found in plant materials, has been shown to have positive effects on intestinal health. However, there is limited research on the specific effects of different types of pectin on fish. This study aimed to investigate the effects of different dietary types of pectin on the growth performance and intestinal health of pearl gentian grouper ( Epinephelus fuscoguttatus female x E. lanceolatus male). Four experimental diets were formulated, including an 8 % common low-ester pectin (CLP) diet, 8 % amidated low-ester pectin (ALP) diet, 8 % high-ester pectin (HP) diet, and a control diet in which 8 % pectin was replaced by 8 % dextrin. Each diet was randomly assigned to triplicate groups of 35 juvenile groupers (6.66 +/- 0.07 g) per tank in a rearing system for 10 weeks. Daily growth coefficient and feed conversion ratio were calculated to assess growth performance, while intestinal mucosal barrier function as well as intestinal physical, chemical, immune, and biological barrier was evaluated to assess intestinal health. The results indicated that dietary inclusion of 8 % pectin generally promoted the growth performance of grouper, but significant difference was observed only in the ALP group. The various type of pectin decreased the intestinal lipase activity and plasma lipopolysaccharide level, increased the intestinal total antioxidant capacity, and down-regulated the expression of intestinal TNF-alpha and IL- 8 but up-regulated the expression of intestinal IL-10. Moreover, dietary 8 % ALP inclusion increased the alkline phosphatase activity, mucoprotein 2 content and the expression level of zonula occludens and Claudin3 in the intestine; while dietary 8 % CLP inclusion increased the intestinal mucoprotein 2 content but decreased intestinal muscularis thickness. Dietary 8 % CLP and ALP inclusion notably increased the relative abundance of Turicibacter and Cetobacterium in the intestine, with Turicibacter contributing to short-chain fatty acid production and Cetobacterium producing vitamin B12, both of which have positive implications for fish health. In conclusion, dietary 8 % ALP inclusion increased the relative abundance of beneficial bacteria in the intestine, enhanced the content of mucoprotein 2, suppressed intestinal inflammation, promoted tight junctions in intestinal cells, reduced intestinal permeability, and facilitated nutrient absorption, thereby supporting the growth of pearl gentian grouper, suggesting the potential of ALP as an additive for enhancing growth and gut health in marine fish.