Brewers’ spent grain as fish feed ingredient: Evaluation of bio-safety and analysis of its impact on gut bacteria of Cirrhinus reba by 16S Metagenomic sequencing

A comprehensive eight week feeding trial was conducted to investigate the potential of brewers' spent grain (BSG) as a sustainable fish feed ingredient. The study assessed both the biosafety of BSG and its impact on the gut microbiome of Cirrhinus reba, utilizing advanced 16S metagenomic sequencing techniques to analyze the composition and diversity of gut bacteria. A total of 90 healthy C. reba juveniles (average weight: 12 ± 1 g) were divided into two dietary groups [for control (C), for BSG meal (tB)] in triplicates. Feed prepared with conventional ingredients was used to feed the control group (C). The group tB was fed with BSG meal. After the feeding trial, the fish in tB group showed significantly higher (p < 0.05) growth parameters as compared to the control group. The results of bio-safety assessment indicated the absence of any pathological symptoms in the BSG meal fed carps. The fish in tB group didn't show any histopathological abnormality. Fish fed the Brewers' Spent Grain exhibited significantly elevated serum biochemical parameters, including alanine transaminase (ALT) and aspartate transaminase (AST), compared to the control group (p < 0.05). 16S Metagenomic sequencing of the fish gut microbiota provides insights into how BSG inclusion affects microbial diversity and composition within the digestive tract of C. reba. The analysis revealed the existence of 240 and 250 diverse bacterial genera in the gastrointestinal tract (GIT) of C. reba in dietary groups C and tB respectively. Importantly, the study found the gut of fish in tB group to be dominated by different beneficial genus including Bacillus, Lactobacillus, Bifidobacterium, Paenibacillus, and Lysinibacillus. Feeding C. reba with BSG meal significantly increased the alpha diversity of the gastrointestinal microbiota, as evidenced by elevated Chao 1 estimator and Shannon index values compared to the control diet (p < 0.05). This study provides comprehensive evidence for the bio-safety of BSG as a sustainable feed ingredient in aquaculture, demonstrating its potential to support healthy fish growth and development. Moreover, the prebiotic potential of BSG in fish has also been highlighted.