Growth, gut dimension, immune change and impact of Aeromonas hydrophila in Nile Tilapia (Oreochromis niloticus) fed Onion (Allium cepa. L) fortified diets.

Abstract This study investigated effects of powdery Onions (Allium cepa) on the growth, gut area, innate immune reaction of Oreochromis niloticus and ability to resist Aeromonas hydrophila challenge. Six 35% crude protein diets were prepared adding fresh onions at 0.0% (OP0), 0.5% (OP1), 1.0% (OP2), 1.5% (OP3), 2.0% (OP4) and 2.5% (OP5) levels. Diets were allotted to triplicate groups of fish (1.79±0.14g) twice daily to apparent satiation for 12 weeks. Fish in each treatments were then challenged with Aeromonas hydrophila and followed for 2 weeks. After 84 days of feeding, growth was not significantly (P>0.05) varied by onion powder. Percentage survival rates was higher in fish fed onion supplements with a regression equation (Y = 75.655 – 10.423X – 1.399X2). Total heterotrophic count (THC) increased with higher inclusion of onion. . Red blood cells were higher in fish fed onion based diets in comparison to OP0 with values ranged from 1.68 x106/µL in OP0 to 2.83 x106/µL in OP1. Alkaline phosphate was higher in fish fed onion supplements. Villi height and width showed no significant variation across treatments. Relative survival was highest in fish fed onion powder supplements when challenged with Aeromonas hydrophila. This study showed onion powder improved survival of Oreochromis niloticus, but did not affect growth and nutrient utilization.