Efficacy of two avermectins, doramectin and ivermectin against Argulus siamensis infestation in Indian major carp, Labeo rohita

The efficacy of two avermectins, doramectin and ivermectin via oral and parenteral routes and their prophylactic effects against Argulus siamensis infestation in Indian major carp, Labeo rohita was studied. Doramectin and ivermectin were fed once to L. rohita sub-adults naturally infested with A. siamensis parasites at graded levels of 1000, 750 and 500μg/kg body weight and 500, 300 and 200μg/kg body weight, respectively. The mean time of clearance of parasites was 24±0.149h for 1000 and 24±0.210h for 750μg of doramectin/kg body weight fish, however, the dose of 1000μg resulted in adverse reactions and mortality in fish. A single dose of 500μg/kg body weight of ivermectin also cleared the infestation in 24±0.258h. In second experiment, L. rohita naturally infested with A. siamensis were administered with doramectin and ivermectin intramuscularly as single dose of 200, 150 and 100μg/kg body weight. Both doramectin and ivermectin at 200μg/kg body weight cleared the infestation in 4±0.149 and 4±0.258h respectively, however, those resulted in adverse reactions viz., black pigmentation, lethargy and poor appetite in fish. The mean time of clearance of parasites from fish was 6±0.210 and 12±0.314h for doramectin and ivermectin, respectively, when given at a lower dose of 150μg/kg body weight. The prophylactic effects of both drugs were also evaluated by challenging naïve rohu with metanaupliar larvae of A. siamensis after feeding the fish single dose of the doramectin and ivermectin at 750 and 500μg/kg body weight, respectively. The effects of both the drugs were found to last for 17–18 days. The effects of bath treatment with doramectin and ivermectin at different concentrations on adult A. siamensis and metanaupliar larvae of A. siamensis were also evaluated. The results suggested that ivermectin could act more rapidly compared to doramectin. However, detailed studies on the toxicity and pharmacokinetics of doramectin and ivermectin upon their administration to aquatic organisms and the environmental impacts of their usage are required to be undertaken before finally recommending the safe use of these drugs for control of parasitic infections.