Dietary Bacillus species modulate lipid metabolism-related parameters, growth, water quality, and bacterial load in Nile tilapia (Oreochromis niloticus )

Abstract

This study examined the impact of supplementing Bacillus spp. mixtures at concentrations of 0.2 g/kg (PRO-0.2) and 0.5 g/kg (PRO-0.5) on Nile tilapia (Oreochromis niloticus) for 90 days. Fish groups receiving PRO-0.2 and PRO-0.5 exhibited significantly lower water ammonia levels than the control group, in linear and quadratic patterns. Furthermore, their length and weight increased exponentially over time, peaking at the end of the experiment. After 90 days, the PRO-0.5 group displayed the highest mean weight gain. Additionally, both the PRO-0.2 and PRO-0.5 groups had the lowest food conversion ratios and highest protein efficiency ratios in a linear pattern. They also showed improved liver function, as indicated by lower levels of liver enzyme (aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase) compared to the control group. In terms of the lipid profile, the PRO-0.2 and PRO-0.5 groups had significantly lower serum levels of low-density lipoprotein, triglycerides, in linear and quadratic patterns, and cholesterol compared to the control group, with no significant differences in cholesterol levels. High-density lipoprotein increased significantly in both PRO-0.2 and PRO-0.5 groups after 90 days, following a linear pattern. Hepatic alkaline phosphatase levels decreased in both the PRO-0.2 and PRO-0.5 groups, following a significant linear pattern over time. After 30 days, the expression of hepatic fatty acid binding protein 3 (fabp3) significantly decreased in the PRO-0.5 group. Intestinal cluster of differentiation 36 (cd36) and fabp3 expression markedly increased, with cd36 showing the greatest rise. After 90 days, hepatic cd36 expression became prominent in both PRO-0.2 and PRO-0.5 groups. Expression of fas was significantly downregulated in both the PRO-0.2 and PRO-0.5 groups. Notably, hepatic lipoprotein lipase (lpl) expression significantly increased in the supplementation groups after 30 days but decreased significantly after 90 days. Overall, this study highlights the positive impact of dietary mixtures of Bacillus spp. on various aspects, including water quality, growth performance, feed utilization, survivability, expression of lipid metabolism-related genes, lipid profile, body composition, and bacterial load in both water and fish bodies.