Abstract Fish gills are commonly attacked by Dactylogyrus vastator , which can quickly infect entire fish stocks and result in biological and financial losses. Chemotherapy remains the preferred option of treating D. vastator infestation in fish farm but these chemotherapy medications can have serious adverse effects and are costly. There must be new and environmentally acceptable therapies for the treatment and control of such kind of parasitic infestations in fishes. In order to control this potential parasite infestation, our study investigated the utilization of herbal leaves mixture extract (HLME) as a functional feed supplement. Four different isonitrogenous diets (300 g/kg crude protein) containing 0 g (control), 2 g, 4 g, or 6 g of HLME/kg of diet were prepared. For eight weeks, juvenile Oreochromis niloticus (Nile tilapia) weighing 5.1±0.09 g were fed with assigned diet six times a day until they appeared satiated. Following that, fish of each treatment group were treated with the solution of D. vastator (40 individual/L of water) for 14 days, they were rigorously watched for any signs of fish mortality. While fish survival was unaffected (P = 0.326), dietary HLME levels considerably increased fish feed intake (P=0.001), body weight gain (P=0.003), and specific growth rate (P=0.001). Likewise, notable elevations were recorded in the concentration of PVC (P=0.003), Hb (P=0.011), RBCs (P=0.001), WBCs (P=0.004), and PLT (P=0.001) in Nile tilapia fed with enriched diets. Antioxidant profiles of fish fed with diet having various levels of HMLE were significantly elevated (P<0.05), while MDA level showed significant (P=0.001) decrease due to supplementation of HMLE in the diet of Nile tilapia. The immune response of fish suggested maximum elevation in activities of respiratory burst (1.3 mg mL −1 ; P=0.001)) and lysozyme activities (13.1 unit mg −1 protein; (P=0.013)), when they were fed with diets enriched with 6 g HMLE kg −1 diet. However, fish fed with the control diet presented the lowest values of these parameters. Additionally, there was a high and directly proportional decrease in post-challenge mortality in fish fed HLME. Fish nourished with 6 g HLME/kg diet showed a significantly lower (P=0.001) mortality rate (3.0%) as compared to the control group (54.6%). Overall, it can be concluded that HLME has not shown any ill effects on the well-being of Nile tilapia and optimal value (4.0 g/kg of diet) ameliorated immune response, intestinal morphometry, and antioxidant performance as well as resistance to Dactylogyrus vastator .
Paray et al. (Wed,) studied this question.