Abstract
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.