Hydrolysed wheat gluten as part of a diet based on animal and plant proteins supports good growth performance of Asian seabass (Lates calcarifer), without impairing intestinal morphology or microbiota

Abstract

A trial was conducted to determine the effect of 6% hydrolysed wheat gluten (HWG) inclusion in a low-fishmeal diet on growth performance and intestinal microbiota and morphology of Asian seabass (Lates calcarifer). Fish (initial average weight of 36.3g) were allocated into floating cages (eight replicates per diet, 30 fish per cage). They were fed either a fishmeal-based diet (positive, diet code: POS; 36% fishmeal), or a diet based on a mix of animal and plant proteins (negative, diet code: NEG). The fishmeal inclusion rate in this diet was reduced to 6%, with the major protein sources being soybean meal and animal by-products. The third diet (diet code: HWG) was similar to the NEG diet with the exception that 6% HWG was included in replacement of the other proteins. At the end of the 48day trial, fish were sampled for intestinal microbiology and histology. Growth parameters were also assessed. Final body weight, SGR and daily feed intake were not significantly different across diets. However, the feeding rate was significantly affected, with the lowest rate observed in the POS treatment and the highest with the NEG treatment. The FCR was significantly lower for both POS and HWG fed fish than for the NEG fed fish. High throughput sequencing revealed that the majority of reads derived from the mucosa samples belonged to members of Proteobacteria (70.3% of the reads), Cyanobacteria (10.0%) and Firmicutes (7.6%). In the digesta reads were mainly assigned to Proteobacteria (34.5%), Fusobacteria (34.5%), and Firmicutes (22.6%). The alpha diversity did not differ among dietary treatments. Some differences in OTU relative abundances were obtained between diets, however, the overall community was not modified to a large extent by HWG. Histological appraisal revealed that the HWG fed fish exhibited significantly higher posterior intestinal perimeter ratio than that of the POS treatment. Overall, including HWG in a low fishmeal diet positively affects feed efficiency. Concomitantly the absorptive surface area of the posterior intestine was improved while the intestinal microbiota, described comprehensively here for the first time in Asian seabass, was similar to the microbiota of other healthy carnivorous marine fish species. The mechanisms involved in these changes may be related to the high glutamine content and to the high protein digestibility of HWG. Statement of relevanceFishmeal used to be the major source of proteins, especially for marine fish and salmonids. Nevertheless, its inclusion in diets has been reduced. Some commercial fish feeds may contain less than 10% fishmeal, largely replaced by a mix of animal and plant proteins. Our manuscript demonstrates that hydrolysed wheat gluten may be used to formulate high quality low fishmeal diets.