<i>Saccharomyces cerevisiae</i> 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 (<i>Saccharomyces cerevisiae</i>) supplementation on growth, immune-related gene expression, and disease resistance in Nile tilapia (<i>Oreochromis niloticus</i>) during the winter season. Fish (an average 5.17 ± 0.33 g) were fed diets containing four different <i>S. cerevisiae</i> 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 (<i>p</i> < 0.05). Additionally, fish-fed the T4 diet showed lower carcass yields but higher fillet yields, along with increased amylase and protease activities (<i>p</i> < 0.05). Significant increases (<i>p</i> < 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 <i>il-8</i> transcription in the liver was noted in fish feeding <i>S. cerevisiae</i> (T2-T4) compared to the control group. In a challenge test against <i>Streptococcus agalactiae</i>, survival rates (SRs) were significantly higher in fish-fed the T4 diet compared to the control group (<i>p</i> < 0.05). Interestingly, the lowest bacterial counts were recorded in the T3 group (<i>p</i> < 0.05). These findings suggest that dietary supplementation with <i>S. cerevisiae</i> at 10-20 g/kg enhances growth performance, digestive enzyme activity, immune responses, and disease resistance in Nile tilapia during winter conditions.