Efficacy of Aqui-S, formalin and praziquantel against the monogeneans, Benedenia seriolae and Zeuxapta seriolae, infecting yellowtail kingfish Seriola lalandi lalandi in New Zealand

This study assessed the efficacy of bath administrations of Aqui-S, formalin and praziquantel against adults and eggs of Benedenia seriolae and Zeuxapta seriolae, two monogenean ectoparasites of kingfish (Seriola lalandi lalandi). Our results showed that 2.5 ppm praziquantel administered for either 24 or 48 It was the most effective treatment for removing B. seriolae (>99%). However, B. seriolae treated with praziquantel for 24 h deposited viable eggs. Formalin at 250 and 400 ppm for 1 h followed by a 5 min freshwater dip was less effective for removing B. seriolae (ca. 80%), but both treatments inhibited the production of eggs by treated parasites. However, a large proportion of B. seriolae eggs exposed to either formalin treatment remained viable. Praziquantel (2.5 ppm for either 24 or 48 h) and formalin (400 ppm for 1 h + 5 min f/w dip) were the most effective treatments for removing Z. seriolae from the gills of kingfish (>99%) but the parasites thus removed continued to deposit viable eggs. Exposure to the anaesthetic Aqui-S did not significantly increase numbers of B. seriolae or Z. seriolae removed front the host above those of the control, but it was ineffective in preventing the production of eggs by treated parasites, and did not reduce egg viability. Eggs of B. seriolae were not prevented from hatching unless exposed to air for a period greater than 3 h, and Z. seriolae eggs were only prevented from hatching if exposed to air for periods greater than 5 h prior to the development of eyespots. These results indicate that both primary and secondary treatments will be required to successfully control B. seriolae and Z. seriolae infections in captive kingfish. (C) 2004 Elsevier B.V. All rights reserved.