Effects of dietary supplementation of garlic (Allium sativum) extract on the resistance of Clarias gariepinus against Edwardsiella tarda infection

The effects of dietary supplementation of garlic (Allium sativum) extract on the growth and disease resistance of African catfish, Clarias gariepinus was evaluated. Also in-vitro evaluation of susceptibility of fish-borne multidrug resistant (MDR) pathogenic bacteria to aqueous extract of garlic was done. Aqueous garlic extract exhibited inhibitory activity against MDR bacteria and the degree of inhibition increased significantly with increasing concentration of garlic extract. The garlic supplementation at the rate of 10g/ kg feed improved the food conversion ratio, specific growth rate and protein efficiency ratio of C. gariepinus significantly (p < 0.05). On the other hand, it increased the disease resistance of C. gariepinus significantly when challenged with Edwardsiella tarda (p>0.05). No significant difference was observed between plasma protein and glucose levels of the control treatment and garlic supplemented treatment during the 56 days of the experiment. Additionally significant differences in plasma protein and glucose levels of control and garlic supplemented treatments in 2 days and/or 15 days post-challenge. The varying levels of plasma glucose and protein suggested that the stress posed by the bacterial infection persisted in fish even after 15 days of challenge. The results demonstrated that bacterial infection can negatively alter blood biochemical profile of C. gariepinus, and dietary supplementation of garlic extract would help improve the resistance of fish to E. tarda infection in culture condition.