Growth, gut dimension, immune response and resistance to Aeromonas hydrophila in Nile Tilapia (Oreochromis niloticus) fed Onion (Allium cepa. L).

This study evaluated onion (Allium cepa) powder in Oreochromis niloticus diets, focusing on growth, gut area, immune response, and resistance to Aeromonas hydrophila. Six diets, OP0, OP1, OP2, OP3, OP4, and OP5 with onion powder inclusion from 0% to 2.5%, were formulated and fed to triplicate groups of fish (1.79±0.14g) for 10 weeks. Fish were then challenged with A. hydrophila and monitored for 14 days. While growth was not significantly altered by onion supplementation over 10 weeks, survival after Aeromonas hydrophila challenge was significantly improved. Bacterial diversity and total counts increased in gut onion-fed fish, with Bacillus and Enterobacter being the dominant species. Serum biochemistry indicated reduced alanine aminotransferase and aspartate aminotransferase levels in fish fed 0.5% to 1.5% onion diets, while alkaline phosphatase increased. Antioxidant enzyme activities were generally higher in onion-supplemented groups, with reduced levels of malondaldehyde. Villi height and width did not significantly differ across treatments. Aeromonas hydrophila challenge on Nile tilapia showed a significantly higher relative percentage survival (RPS) in onion-supplemented groups, with a record 100% in groups fed 1.0% and above. This study revealed that 1-1.5% inclusion of onion in the diets of Nile tilapia resulted in enhanced immune response, gut health, and disease resistance