Effects of using vital wheat gluten in practical diets on growth, intestinal histopathology, proinflammation-related gene expression, and resistance of white seabream (Diplodus sargus) to Staphylococcus epidermidis infection

Abstract

The current study was carried to assess the effects of using vital wheat gluten (VWG) as a fishmeal (FM) replacer in practical diets for white seabream, Diplodus sargus, juvenile. Five isonitrogenous (~ 40% CP) and isoenergetic (21 MJ/Kg diet) diets were formulated to replace FM protein by VWG protein at levels of 0.0 (CTR), 15 (VWG15), 30 (VWG30), 45 (VWG45), and 60% (VWG60). Fish (1.7 ± 0.1 g) were fed on the experimental diets in triplicated groups up to apparent satiety for 10 weeks. At the end of the feeding trial, fish of each treatment were intraperitoneally injected by pathogenic bacterium Staphylococcus epidermidis and observed for further 10 days. Results showed that only fish fed VWG45 and VWG 60 diets showed significant lower growth and feed intake relative to all other VWG groups. VWG at all inclusion levels did not significantly affect survival rate, proximate composition, or body morphometry of white seabream. The intestine architecture indicated that fish fed the VWG45 diet had mild alterations with abundant absorptive vacuole in the middle intestine, while mild to moderate pathological changes were observed in the distal portion. The intestine of fish fed VWG60 showed severe degeneration with signs of inflammation. Additionally, villi length/width and absorption area in foregut, midgut, and hindgut of white seabream were not significantly changed among CTR, VWG15, and VWG30 but these measurements were significantly lowest at the VWG60 treatment. Comparing with the CTR group, highest IL-1β and TNF-α gene expressions were observed in VWG60 followed by VWG45 groups. The phylogenetic tree indicated that VWG induced changes in muscles protein pattern especially at the VWG60 group. After the bacterial challenge, fish fed 15 and 30% VWG protein showed mild mortality as the control fish (43.3–46.7%); meanwhile fish fed the VWG60 diet were more susceptible to S. epidermidis infection showing highest mortality (63.3%). In conclusion, the present findings elucidated that the performance of white seabass was not significantly affected by partial replacement of 30% FM protein with VWG protein.