Effects of Azadirachta indica Leaf Aqueous Extract supplemented Fish Diets on Innate Immune Response and Disease Resistance of Tilapia (Oreochromis niloticus)

Abstract

Pseudomonas fluorescens is an important bacterial pathogen causing economic losses in aquaculture worldwide. The adverse effects of antibiotics raise public concerns on using them in aquaculture. The objective of this study was to examine the effectiveness of aqueous extract of Azadirachta indica leaves on nonspecific immunity and disease resistance in tilapia (Oreochromis niloticus). Fish diets supplemented with aqueous extract of A. indica at the concentrations of 0% (Diet 1), 1% (Diet 2), 1.5% (Diet 3) and 2% (Diet 4) were investigated for their effects on nonspecific immune response and disease resistance in tilapia. The fish given diet 3 and diet 4 for 3 weeks had increased levels of leukocyte phagocytic activity though higher activity was observed in diet 4 group. Diet 3 and diet 4 also enhanced plasma lysozyme activity in tilapia. The similar levels of lysozyme activity were found in the fish receiving both diets for 3 weeks. Only diet 4 had stimulatory effect on respiratory burst activity in tilapia. This effect was observed 3 weeks after feeding the fish with diet 4. Throughout the experiment, no significant differences (P > 0.05) in phagocytic, lysozyme and respiratory burst activities were found between group fed with diet 1 (control) and diet 2. Following 3 weeks after feeding, fish were infected with Pseudomonas fluorescens at median lethal dose (LD50). No mortality was found in the diet 4 group while 50%, 48% and 28% of cumulative mortality were found in the fish receiving diet 1, 2 and 3 respectively. These results indicate that the aqueous extract of A. indica may elevate the nonspecific immune response and enhance disease resistance in tilapia.