Physiological Benefits of Probiotic Refeeding After Short-Term Fasting in Nile Tilapia: Growth Performance, Histomorphological, and Gene Expression Responses

This study investigated the physiological benefits of probiotic supplementation during refeeding after short-term fasting in Nile tilapia (Oreochromis niloticus). A total of 180 fish were assigned to three groups: continuously fed control or subjected to 5 days of fasting followed by 15 days of refeeding with either a basal or probiotic-enriched diet containing Bacillus subtilis, B. licheniformis, and B. pumilus. Growth performance indices (body weight, length, weight gain, specific growth rate, condition factor, relative feed intake, and feed conversion ratio) were measured. Muscle samples were collected for histomorphological evaluation and quantitative real-time PCR analysis of antioxidant genes catalase (cat) and superoxide dismutase 2 (sod-2), growth-related genes insulin-like growth factor 1 (igf-1) and suppressor of cytokine signaling 2 (soc-2), anti-inflammatory gene transforming growth factor beta (tgf-β), and myostatin genes. Fasting significantly reduced (p < 0.05) body weight compared to control, confirming the impact of nutrient deprivation. Upon refeeding, fish on the basal diet showed partial growth recovery but remained below control levels, whereas probiotic-fed fish exhibited superior recovery, surpassing both control and basal groups in body weight, length and weight gain. Condition factor exhibited insignificant changes among all groups after fasting and upon refeeding. Specific growth rate of the entire experiment was highest in the probiotic group, while insignificant. Relative feed intake decreased in both refed groups, yet feed conversion ratio improved, particularly with probiotics. Gene expression analysis revealed fasting-induced upregulation of antioxidant (cat and sod-2) and myostatin (p < 0.05), alongside downregulation of growth-related (igf-1 and soc-2) and anti-inflammatory (tgf-β) genes (p < 0.05). Basal refeeding restored most expressions, whereas probiotics enhanced antioxidant, growth, and anti-inflammatory genes while normalizing myostatin (p > 0.05 vs. control). Histological evaluation showed fasting-induced muscle atrophy, which was most effectively reversed by probiotics. Overall, probiotics accelerated recovery, highlighting their potential to optimize post-fasting growth in aquaculture.