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 500 μg/kg
body weight and 500, 300 and 200 μg/kg
body weight, respectively. The mean time of clearance of parasites was 24 ± 0.149 h for 1000 and 24 ± 0.210 h for 750 μg of
doramectin/kg
body weight fish, however, the dose of 1,000 μg resulted in adverse reactions and mortality in fish. A single dose of 500μg/kg
body weight of
ivermectin also cleared the infestation in 24 ± 0.258 h. In second experiment, L. rohita naturally infested with A. siamensis were administered with
doramectin and
ivermectin intramuscularly as single dose of 200, 150 and 100 μg/kg
body weight. Both
doramectin and
ivermectin at 200 μg/kg
body weight cleared the infestation in 4 ± 0.149 and 4 ± 0.258 h 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 ± 0.314 h for
doramectin and
ivermectin, respectively, when given at a lower dose of 150 μg/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 500 μg/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.