| Summary: | An 8-week feeding trial was conducted to investigate whether extruded soybean meal (ESBM) replacing fish meal (FM) in the feed affect the growth performance, plasma components and intestinal barrier of Epinephelus coioides. Five isonitrogenous, isocaloric experimental diets were formulated using ESBM substitution for FM protein at incremental levels of 0, 15%, 30%, 45%, 60%. Each diet was randomly assigned to one of the five groups with triplicate tanks of 20 juvenile fish with an average initial weight of (52.97 ± 0.10) g, and hand-fed twice daily across the feeding trial. Weight gain rate, specific growth rate, feed efficiency, feed intake and the whole-body lipid had negative linear and/or quadratic responses to dietary ESBM inclusion levels. There are similar patterns for the plasma levels of HDL-C, LDL-C, TP, TC, TG, C3, and IgM, but the opposite trend was observed for plasma endotoxin and endothelin-1 levels. The trypsin activity in mid intestine (MI) and distal intestine (DI) and protease activity in DI showed negative linear and quadratic responses to increasing dietary ESBM inclusion levels. The muscle layer thickness of MI and the mucosal fold length and muscle layer thickness of DI showed negative linear and quadratic responses to increasing dietary ESBM inclusion levels. The mRNA levels for IL-8 in MI and DI, IL-10 in the three intestinal segments (proximal intestine (PI), MI, and DI), IL-1β, IL-12 and TNF-α in PI showed positive linear and/or quadratic responses to increasing dietary ESBM inclusion levels, whereas negative linear and/or quadratic responses were observed for TGF-β1 mRNA levels in MI and DI. The above results indicate that dietary ESBM inclusion at above 45% FM protein could reduce the growth performance and immunity of grouper by reducing intestinal digestive capacity and plasma lipid levels, as well as inducing inflammatory reactions.
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