Effects of diet containing germinated faba bean (Vicia faba L.) on the intestinal health and gut microbial communities of Nile tilapia (Oreochromis niloticus)

Crisp Nile tilapia (Oreochromis niloticus) is a valuable fish product with high muscle firmness and chewiness generated by dietary faba beans (Vicia faba L.). However, the overconsumption of faba bean could induce intestinal inflammation in Nile tilapia due to its endogenous anti-nutritional factors (ANFs). Germination has been cited as an effective method for reducing ANFs in faba beans. But, the effects of germinated faba beans on the tilapia remain unclear. In this report, Nile tilapia were fed a diet supplemented with dry faba beans (FB0), or germinated faba beans (FB5), or a basal diet (control) for 75 days. Thereafter, samples of the fish were examined for textural quality, digestive enzyme activity, histology of the inner intestinal wall, expression of related genes, and composition of intestinal microbes. The hardest fillets were obtained from the FB5 (406.17 ± 42.51 gf) group, followed by the FB0 (301.17 ± 24.70 gf) and control (117.50 ± 8.19 gf) groups. The amylase levels were lower in the FB0 and FB5 groups, whereas the trypsin activities were up to 1.9-fold higher than in the control group. The gene expressions of IL-1β, CCL3, and TNF-α were significantly up-regulated in both the FB0 and FB5 groups, whereas metallothionein expression was down-regulated in the intestine relative to control group. Moreover, expression of IFN-γ and Hsp70 decreased in FB5, but increased in FB0. In particular, the diversity of intestinal microbiota was higher in the FB5 group than in the FB0 group (Fusobacteria abundance significantly decreased from 79.18% to 55.87%, while Proteobacteria abundance decreased from 8.12% to 7.02%), indicating that the intestinal microbiota structure was affected by altered diets. These results indicate that germinated faba bean could be a good substitute for dry faba beans in tilapia culture.