Oral treatments for monogenean parasites of farmed yellowtails, Seriola spp. (Carangidae).

Abstract

Japanese yellowtail Seriola quinqueradiata has been commercially farmed in Japan since the 1940s. In comparison, sea-cage farming of yellowtail kingfish Seriola lalandi in Australia is still developing, with commercial production commencing in 1998. In Australia, S. lalandi is parasitised by Zeuxapta seriolae and Benedenia seriolae. In Japan, S. quinqueradiata is parasitised by Heteraxine heterocerca and B. seriolae. These monogeneans affect industries in both countries and management of these parasites is required to prevent impacts on fish health and commercial losses. I investigated efficacy (% reduction of mean parasite abundance) for orally administered praziquantel, fenbendzole and oxfendazole against Z. seriolae and B. seriolae on S. lalandi and the efficacy of orally administered praziquantel and febantel against H. heterocerca and B. seriolae on S. quinqueradiata. Medications were administered to fish by surface coating feed pellets or via direct intubation of the stomach. Seriola lalandi administered fenbendazole and oxfendazole by surface coating of feed had lower abundance of the gill parasite Z. seriolae. Seriola quinqueradiata intubated with febantel had lower abundance of the gill parasite H. heterocerca. Neither fenbendazole nor oxfendazole administered to S. lalandi in Australia, nor febantel administered to S. quinqueradiata in Japan resulted in a lower abundance of the skin parasite B. seriolae. Praziquantel was first administered to S. lalandi by surface coating of feed. Fish rejected medicated feed, suggesting praziquantel affected its palatability. Fish treated with feed medicated with praziquantel had fewer Z. seriolae and B. seriolae than untreated fish. Praziquantel administered to S. lalandi by intubation allowed a more accurate dose to be tested without differential feeding or reduced palatability obstructing results, and resulted in fewer Z. seriolae (99.5-100 % reduction) and B. seriolae (91 – 97.7 % reduction). Intubated praziquantel also led to fewer recruitment life stages of Z. seriolae and B. seriolae, even at low doses, but did not completely eliminate them from S. lalandi. Praziquantel administered to S. lalandi alone and combined with cimetidine had high efficacy (>99%) against Z. seriolae. In comparison, praziquantel administered alone resulted in fewer B. seriolae (68.3 – 69.7 % reduction) than the same doses of praziquantel combined with cimetidine (36.9 – 40.9 % reduction). A 90.4 -100% reduction in H. heterocerca was achieved when praziquantel was administered by intubation to S. quinqueradiata in Japan but there was only a 22-77.8 % reduction in B. seriolae. The dose of PZQ (150 mg kg⁻¹ body weight day⁻¹ for 3 days) on the label of a commercially available product used to treat B. seriolae in Japanese aquaculture resulted in a 50.9% reduction against B. seriolae, but completely eliminated H. heterocerca. In trials against Z. seriolae and B. seriolae on S. lalandi in South Australia, I also screened 27 other anthelmintics and antiparasitics from the chemical groups: amprolium derivatives, benzimidazoles, benzyl ureas, diphosphate salts, imidazothiazoles, macrocyclic lactones, nitromidazoles, organophosphates, piperazines, salicylanilides, substituted phenols and tetrahydropyrimidines. Of these, only the benzimidazole, albendazole, was effective against Z. seriolae and none appeared to have an effect against B. seriolae.