Efficacy of the dehydrated lemon peels on the immunity, enzymatic antioxidant capacity and growth of Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus)

This work was performed to investigate the effect of the dietary addition of lemon, Citrus limon (L.) Burm. peels on the growth performance, antioxidant activity, immune status, and disease resistance against Aeromonas hydrophila in two common freshwater fish species (Nile tilapia, Oreochromis niloticus and African catfish, Clarias gariepinus). The fishes were randomly distributed at 10 fish per 60 L aquariums, and fed on three different diets (a control basal diet and two supplemented diets with 1% and 2% dried C. limon peels powder) for 45 days. The growth performance was insignificantly decreased in Nile tilapia fed on 2% followed by 1% C. limon peels supplemented diets and in African catfish fed on 2% C. limon peels when compared with the control fishes. Serum glucose was decreased with increasing levels of C. limon peels (2% followed by 1%) in Nile tilapia diets, whereas no significant effects were observed in African catfish. The cortisol levels remained unchanged in both fish species. However, significant elevation (p < .05) in the level of catalase (CAT) enzyme was seen in both fish species fed on C. limon peels (1% and 2%). Superoxide dismutase (SOD) was significantly increased in African catfish fed on C. limon peels (1% and 2%), whereas no significant change was noted in Nile tilapia. The reduced glutathione (GSH) content was significantly increased in both fish species fed on 2% C. limon peels; whereas no significant change was detected when they fed on 1% C. limon peels. The C. limon peels supplemented diets enhanced the serum lysozymes activity, myeloperoxidase (MPO) level and the phagocytic activity in both fish species. Moreover, nitric oxide level was significantly increased in Nile tilapia fed on 1% and 2% C. limon peels, while no significant change was observed in African catfish. The relative percentage survival (RPS), post A. hydrophila challenge, was found to be boosted in both fish species fed on C. limon peels (1% and 2%), when compared with the control fishes. The results elucidated that the inclusion of C. limon peels in Nile tilapia and African catfish diets could improve the enzymatic antioxidant capacity and immune response, but no significant effect on growth performance was observed. Thus, C. limon peels as a by-product could be successfully used as a cheap feed additive in aquaculture to enhance disease resistance.