LAUSR

Abstract Dactylogyrus vastator is a hermaphroditic monogenean ectoparasite that attacks fish gills and can rapidly infect entire fish stocks causing economic losses. Chemotherapy is still the first choice among drugs used for the treatment of monogenean infections. However, these chemo-drugs are expensive and may have severe side effects. Hence, there is a need to find out alternative and eco-friendly therapeutics to control and treat these parasitic diseases in fish. Therefore, the present study was conducted to assess the use of dietary Tridax procumbens leaves extract (TPLE) as a functional feed additive to control this possible parasitic infection. Four isonitrogenous diets (300 g/kg crude protein) were prepared to contain 0.0 (control), 2, 4, or 6 g TPLE/kg diet. Nile tilapia, Oreochromis niloticus, juveniles (4.6 ± 0.06 g) were fed one of the experimental diets up to apparent satiation thrice a day for 8 weeks. After that, fish from each treatment were exposed to D. vastator solution (40 individual/L) and closely monitored for any fish mortality for 14 days. It is noted that dietary TPLE levels significantly promoted the fish growth and feed consumption but feed conversion ratio and fish survival were not affected. Additionally, dietary TPLE levels significantly enhanced villi length/width and absorption area of fish intestine. Dietary TPLE significantly elevated the antioxidant and immunity responses. Also, post-challenge mortality in TPLE-fed fish was significantly reduced in a directly proportional manner. The lowest fish mortality (10.0%) was observed in fish fed a diet containing 6 g TPLE/kg diet, while highest mortality (36.7%) was recorded in the control fish group. The current study concluded that dietary TPLE has no harm effect on fish welfare and stimulated fish performance, intestinal morphometry, antioxidant, and immunity responses of Nile tilapia as well as its resistance to D. vastator infection with optimum levels of 4–6 g/kg diet.