Onion Powder and Probiotics Synergistically Improve Growth Performance and Immune Response in Stinging Catfish

Given the rising concerns about antibiotic resistance in aquaculture, the increasing need for sustainable, eco‐friendly alternatives has been highlighted. In response, a 45‐day feeding trial was conducted to evaluate the efficacy of dietary onion powder and probiotics as natural growth promoters and immune enhancers in stinging catfish ( Heteropneustes fossilis ). The study tested six dietary treatments: a basal diet (without prebiotics and probiotics, control), O (2% onion powder + basal diet), P (4% probiotics + basal diet), and three combined treatments—OP3% (1% onion powder + 2% probiotics + basal diet), OP6% (2% onion powder + 4% probiotics + basal diet), and OP12% (4% onion powder + 8% probiotics + basal diet). The trial aimed to assess their effects on growth performance, feed utilization, intestinal morphology, liver health, and immune response. Among the treatments, the OP6% diet demonstrated the most significant improvements. Fish in this group showed marked increases in weight gain (WG), percentage WG, daily WG, specific growth rate (SGR), hepatosomatic index (HSI%), and viscerosomatic index (VSI%). Feed efficiency also improved, as evidenced by a lower feed conversion ratio (FCR) and higher protein efficiency ratio (PER). Survival rates, however, remained consistent across all groups. Gut health was notably enhanced in the OP6% group, with significant improvements in villi length and width, crypt depth, goblet cell numbers, and overall intestinal architecture. Liver histology also indicated healthier hepatocyte structures. Immunologically, the OP6% diet significantly elevated white blood cell (WBC) counts—including lymphocytes, neutrophils, monocytes, and eosinophils—while basophils remained unaffected. In conclusion, the combination of 2% onion powder and 4% probiotics (OP6%) presents a promising natural alternative to antibiotics, promoting better growth, nutrient utilization, gut health, and immune function in stinging catfish.