Dietary Mitracarpus scaber leaves extract improved growth, antioxidants, non-specific immunity, and resistance of Nile tilapia, Oreochromis niloticus to Gyrodactylus malalai infestation

Abstract

Gryodactylus malalai is a monogenean ectoparasite that causes damage to the skins and gills of the infected fish. It is a viviparous organism and easily transmitted to other fish in an aquatic ecosystem resulting in huge biological and economical losses. The use of chemotherapeutics is the method adopted by farmers in the treatment, and control of monogenean infections. However, the use of these chemotherapeutics has been discouraged because they are costly, have residual effects on fish tissues, and contribute to environmental pollution. Thus, a substitute for synthetic chemotherapeutics needs to be investigated and developed. Effects of Mitracarpus scaber leaves extract (MSLE) on growth, antioxidants, immunity, and resistance of Nile tilapia, Oreochromis niloticus to G. malalai infestation have been examined. Four diets of 300 g/kg crude protein were formulated and fortified with MSLE at 0.0 (control), 2, 4, or 6 g/kg diet. Each diet was fed to Nile tilapia juveniles (3.5 ± 0.02 g) to noticeable satiation three times a day for 56 days. Then, fish were experimentally challenged using bath method by releasing the fish into a solution containing 40 G. malalai per liter for 14 days. The infected fish were observed for any clinical signs and mortality. It was observed that MSLE fortified-diets significantly enhanced the fish growth, feed intake and utilization, but no significant differences were observed in feed conversion ratio and fish survival rate. Further, intestinal villi length, villi width, and absorption area were markedly increased in fish fed MSLE-based diets. Also, hemato-biochemical, antioxidant, and immune indices were significantly improved in Nile tilapia fed dietary MSLE levels. After exposure of fish to parasitic infestation, mortality was significantly decreased in Nile tilapia fed with MSLE-based diets especially at 6 g MSLE/kg diet (5.0%); meanwhile fish fed with the control diet showed the highest mortality (62.9%). Thus, it was concluded that diets supplemented with MSLE promoted fish growth performance, antioxidants, and non-specific immunity of Nile tilapia. Also, resistance of Nile tilapia to G. malalai infestation were elevated when fed MSLE-fortified diets ranged from 5.5–6 g/kg diet.