Saccharomyces cerevisiae Supplementation Enhances Growth and Immune Response in Nile Tilapia During Winter Stress

The purpose of this study was to evaluate the effects of baker’s yeast ( Saccharomyces cerevisiae ) supplementation on growth, immune‐related gene expression, and disease resistance in Nile tilapia ( Oreochromis niloticus ) during the winter season. Fish (an average 5.17 ± 0.33 g) were fed diets containing four different S. cerevisiae concentrations: 0 g/kg (control; T1), 5 g/kg (T2), 10 g/kg (T3), and 20 g/kg (T4) for 90 days. The results showed that weight gain (WG) and specific growth rate (SGR) were significantly higher in fish‐fed the T4 diet compared to the control group ( p < 0.05). Additionally, fish‐fed the T4 diet showed lower carcass yields but higher fillet yields, along with increased amylase and protease activities ( p < 0.05). Significant increases ( p < 0.05) in serum lysozyme activity were found in fish‐fed the T4 supplemented diet, and elevated myeloperoxidase (MPO) levels were observed in fish‐fed the T3 diet. Moreover, upregulation of il-8 transcription in the liver was noted in fish feeding S. cerevisiae (T2–T4) compared to the control group. In a challenge test against Streptococcus agalactiae , survival rates (SRs) were significantly higher in fish‐fed the T4 diet compared to the control group ( p < 0.05). Interestingly, the lowest bacterial counts were recorded in the T3 group ( p < 0.05). These findings suggest that dietary supplementation with S. cerevisiae at 10–20 g/kg enhances growth performance, digestive enzyme activity, immune responses, and disease resistance in Nile tilapia during winter conditions.