Growth and physiological response of Nile tilapia (Oreochromis niloticus) fed a fermented flax meal inoculated with Saccharomyces cerevisiae or Bacillus subtilis

The trial was conducted to evaluate the impacts of substitute fish meal (FM) by fermented flaxseed meal (FFM) on growth, feed utilization, digestive enzyme activity, antioxidant capacity, and physiological responses in juvenile Nile tilapia ( Oreochromis niloticus ). A total of 225 fish were arbitrarily dispersed into five dietary treatments with three replicates each. The basal group received a conventional diet with fish meal, while other groups received diets where YFCSM 25 % and YFCSM 50 % of fermented flaxseed by saccharomyces and (LFCSM 25 % and LFCSM 50 % ) of fermented flaxseed by Bacillus subtilis. The results showed that the LFCSM 25 % had significantly better final body weight, weight gain, feed conversion ratio, protein efficiency ratio, and energy retention versus other groups (P ≤ 0.05). BFCSM and BFCSM also exhibited enhanced digestive enzyme activities (amylase, lipase, and protease), reduced oxidative stress markers (MDA), and increased antioxidant levels (GSH, TAC). Blood biochemical analysis indicated improved liver function. Morphometric measurements obtained showed no significant differences between specimens from different groups Moreover, hepatocytes showed variable degrees of cellular vacuolation. This alteration is significant among groups. In conclusion, replacing 25 % of fish meal with LFCSM improved growth performance, nutrient digestibility, and antioxidant status without adverse effects on health or tissue structure. This dietary approach presents a maintainable and profitable substitute to fish meal in aquafeeds for Nile tilapia. • T4 group had significantly better growth and feed utilization efficiency. • T4 and T5 also exhibited enhanced digestive enzyme activities. • T4 and T5 also exhibited reduced oxidative stress markers (MDA). • Liver function and antioxidant levels improved of fish group fed diets contained fermented cotton seed meals. • Morphometric measurements showed no significant differences between specimens from different groups.