Host impact of monogenean Lepidotrema bidyana infection and intensity estimates for onsite monitoring

Abstract

We developed a rapid effective method for accurate estimation of intensity for the monogenean Lepidotrema bidyana, a gill parasite of silver perch Bidyanus bidyanus. This parasite requires monitoring because high-intensity infections reduce host growth and can lead to secondary bacterial and fungal infections. The most accurate method for counting L. bidyana was visual examination of fresh gills. There was a significant relationship between fish size and parasite intensity; however, there was no significant relationship between fish condition and parasite intensity. Parasite intensity estimates were generated by using the mean intensity of worms on the posterior hemibranch on the first left gill arch, compared to the total mean intensity of worms on all hemibranchs. Estimates were validated by predicting L. bidyana intensity from a random sample of silver perch obtained from aquaculture ponds. Parasite intensity estimates correlated strongly to real counts, and this method can be used to accurately predict parasite intensity on an individual host, and thus represents an improvement over previous methods. KEY WORDS: Monogenea · Bidyanus bidyanus · Lepidotrema bidyana · Prevalence · Intensity Resale or republication not permitted without written consent of the publisherDis Aquat Org 100: [51][52][53][54][55][56][57] 2012 tions. Extrinsic influences include interspecific competition, predation, hyperparasitism and re inforcement of interspecific reproductive barriers (Rohde 1979). The main intrinsic influence is enhance ment of mating success (Rohde 1991, 1993, Geets et al. 1997.In aquaculture, parasite management systems rely on accurate monitoring methods specific to the target species (Grant 1983). When developing specific counting methods, non-random parasite distributions must be considered. Rowland et al. (2006b) monitored Lepidotrema bidyana by sampling 5 Bidyanus bidyanus fish from each treated pond, re moving the anterior-most left gill arch from each fish, examining that arch at 100× magnification, counting the number of parasites in 5 fields of view and reporting the prevalence and mean number of parasites per field of view. Which part or side of the gill should be examined was not specified (Rowland et al. 2006b). Field veterinarians expressed doubt that the method provided accurate intensity estimates. We evaluated this current counting method, and developed a new method to more accurately estimate L. bidyana intensity on an individual host. This method will aid onsite monitoring and research on treatments, and provides information on the relationships between intensity and host growth and condition. We also investigated the relationship between parasite intensity and fish size, and the effect that parasite intensity has on the condition of the host. MATERIALS AND METHODS Source of fish and parasitesSilver perch (n = 660) infected with Lepidotrema bidyana from Pioneer Fish Farm (PFF) (Gloucester, NSW) were maintained in a 10 000 l recirculation tank at Flinders University, South Australia ...

Efficacy of bath and orally administered praziquantel and fenbendazole against Lepidotrema bidyana Murray, a monogenean parasite of silver perch, Bidyanus bidyanus (Mitchell)

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