Lernaea cyprinacea infection in a new host Puntius pulchellus in intensive culture system and its control by doramectin.

The present study explored the susceptibility of Puntius pulchellus subadults to Lernaea cyprinacea infection subsequent upon their first introduction to an intensive culture system that had a previous history of Lernaea infection and evaluated the efficacy of doramectin against the parasite. All the P. pulchellus introduced to the culture pond got infected demonstrating 100 % susceptibility of this species to Lernaea infection. Pathological changes caused by the parasite as evidenced by the extensive hemorrhage and tissue necrosis of the host at the point of parasite attachment was most severe in P. pulchellus. On the contrary, among the fish species already present in the pond and were previously exposed to the infection before the start of the present study, only Labeo fimbriatus developed mild to moderate infection. Cirrhinus mrigala, Ctenopharyngodon idella and Cyprinus carpio from the same culture pond did not develop Lernaea infection. Doramectin administration at 1 mg/kg b.wt. of fish incorporated in feed and given orally for 10 days or by a single intramuscular injection at 200 µg/kg b.wt. was found to be effective in controlling L. cyprinacea adult parasite infection in P. pulchellus. Doramectin hastened healing of the wounds caused by L. cyprinacea and did not cause any noticeable adverse reactions or toxicity to the fish host during the present study. In conclusion, P. pulchellus was observed to be highly susceptible to L. cyprinacea upon its first exposure to the infective stages of the parasite and a single intramuscular injection of doramectin at 200 µg/kg b.wt. was more effective than oral administration of the drug in controlling L. cyprinacea infection.

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 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.

Efficacy of doramectin against natural and experimental infections of Lernaea cyprinacea in carps.

Efficacy of doramectin administered via oral and parenteral routes against experimentally induced and natural infections of the copepod parasite Lernaea cyprinacea in carps was studied. Administration of doramectin incorporated in feed at 1mg/kg b.wt. of fish for 10 days effectively controlled experimentally induced Lernaea infection in Labeo fimbriatus fingerlings within an average of 19 days of post-treatment as compared to the normal course of 41 days. Similarly, doramectin given through feed at 1mg/kgb.wt. of fish for 10 days was equally effective in controlling natural infection of this parasite in the underyearlings of Catla catla and L. fimbriatus. Intramuscular administration of doramectin at 200microg/kgb.wt. of fish effectively removed adult Lernaea infection in L. fimbriatus as early as 18 days of treatment as compared to the time period of 43 days taken by the untreated fish to get rid of the infection. Single intramuscular administration of the drug was more effective against the parasite than its administration in multiple divided doses. In all cases, doramectin did not cause any noticeable adverse reactions or toxicity to the fish host. In view of the handling associated stress and other operational difficulties involved, a single intramuscular administration of the drug at 200microg/kgb.wt. is suggested for treatment of heavily infected adults and brood stock of carps. Doramectin incorporated in feed at 1mg/kgb.wt. of fish is best suited for treatment of Lernaea infection in young fish including fingerlings. However, detailed studies on the toxicity and pharmacokinetics of doramectin upon its administration to aquatic organisms and the environmental impact of its usage are required to be undertaken before finally recommending the safe use of this drug for control of parasitic infections of aquatic organisms.