The Effect of Dietary Wheat Gluten Products on Gut Morphology, Non-Specific Immune Parameters, and Allochthonous Intestinal Microbial Population of Juvenile Rainbow Trout (Oncorhynchus mykiss) Fed with a High Plant Protein Diet

Abstract

Background: Diets for Salmonids contain less fishmeal and more plant (and especially pulse) proteins that can impact gut microbiota, morphology, and non-specific immune system. The objective of the study was to investigate if including 10% of three different types of wheat proteins in a soy-based diet affects in the same manner gut microbiota, morphology and non-specific immune parameters of juvenile rainbow trout. Methods: Over the course of a 66 day nutrition feed trial, triplicate tanks of juvenile rainbow trout (31 fish per tank; initial weight=24.80 ± 0.31 g) were fed three experimental diets containing 10% inclusions of varying types of wheat proteins. Wheat protein inclusions, vital (VWG), hydrolysed (HWG) and a soluble hydrolysed (SWG) were incorporated into a basal feed at the expense of soy protein concentrate (SPC diet). Growth performance was monitored throughout the trial. At the end point intestinal samples were taken for microbial, molecular and histological analysis. Findings: Growth performance was unaffected by 10% dietary inclusions of wheat proteins, especially because growth already achieved high level with the SPC diet, with a feed conversion ratio of 0.99. Modulation of the allochthonous intestinal microbiota at genus level was observed, with increased proportions of Weissella in the 10% VWG treatment compared to the SPC and SWG products. Bacillus relative abundance was significant increased with 10% SWG diet. Leuconostoc was significantly higher with HWG diet. Transcription level expression of TNF-α and Heat Shock Protein 70 (HSP 70) was significantly down-regulated in all wheat protein diets compared to the SPC treatment. A PCA performed on these parameters revealed that SPC diet was significantly associated with the first dimension characterised by high relative abundance of TNF-α, IL10, TGF-β, Glute ST, IL8 and HSP70; while SWG diet was negatively associated with the second dimension which was positively correlated with high relative abundance of IL8 and HSP70 and negatively correlated with relative abundance of IL10 and TGF-β. Increased Intra-epithelial leukocytes (IEL) counts and lamina propria width was observed with 10% VWG and HWG inclusion. Conclusions: All types of wheat proteins are promising plant protein source with the benefits of enhancing growth of potential beneficial bacteria in the intestine, reducing intestinal stress and potentially enhancing the non-specific immune system of rainbow trout fed with a low fishmeal, high pulse diet.