Efficacy of praziquantel against Centrocestus formosanus metacercariae infections in common carp( Cyprinus carpio Linnaeus)

ObjectiveThree treatment regimes were tested for controlling acute gill infections (open gill disease)caused by Centrocestus formosanus in juvenile common carp.MethodA total of 1620 common carp juveniles (70 days old)naturally infected with C.formosanus in the gills at the start of the experiment.The carp fishes were collected and treated with CuSO4,formalin and praziquantel,and compared to controls (kept on a normal diet and without exposure to chemicals)for 6 weeks.ResultInfected fishes exhibited a lower growth rate,both with regard to length and weight.The intensity of metacercarial infections of C.formosanus was reduced throughout the experiment.Praziquantel (50 and 75 mg/kg supplied with feed for 5 days) killed all metacercariae in carp gills.Treated juveniles recovered from the opened gill disease.At the dosage of 25 mg/kg,only 35% of the parasites became inactivated.Immersion and bath in CuSO4 and formalin at all concentrations did not inactivate any metacercariae.Snail-borne trematode diseases should preferentially be controlled by controlling snails and improving hygienic measures.Conclusion The opened gill disease of common carp due to metacercariae of C.formosanus could not be successfully treated by using normal chemicals (CuSO4 or formaline )applied through bathing or immersing methods.However,it can be treated by praziquantel (50-75 mg of praziquantel per kg of feed ) administered through feed for 5 days.