Protozoan parasites of the genus Perkinsus are considered important pathogens responsible for mass mortalities in many wild and farmed bivalve populations. The present study was initiated to screen populations of the Indian edible oyster Crassostrea madrasensis, a promising candidate for aquaculture along the Indian coasts, for the presence of Perkinsus spp. The study reports the presence of P. beihaiensis for the first time in C. madrasensis populations from the Indian subcontinent and south Asia. Samples collected from the east and west coasts of India were subjected to Ray's fluid thioglycollate medium (RFTM) culture and histology which indicated the presence of Perkinsus spp. PCR screening of the tissues using specific primers amplified the product specific to the genus Perkinsus. The taxonomic affinities of the parasites were determined by sequencing both internal transcribed spacer (ITS) and actin genes followed by basic local alignment search tool (BLAST) analysis. Analysis based on the ITS sequences showed 98 to 100% identity to Perkinsus spp. (P. beihaiensis and Brazilian Perkinsus sp.). The pairwise genetic distance values and phylogenetic analysis confirmed that 2 of the present samples belonged to the P. beihaiensis clade while the other 4 showed close affinities with the Brazilian Perkinsus sp. clade. The genetic divergence data, close affinity with the Brazilian Perkinsus sp., and co-existence with P. beihaiensis in the same host species in the same habitat show that the remaining 4 samples exhibit some degree of variation from P. beihaiensis. As expected, the sequencing of actin genes did not show any divergence among the samples studied. They probably could be intraspecific variants of P. beihaiensis having a separate lineage in the process of evolution. KEY WORDS: Edible oyster · Crassostrea madrasensis · Protozoan parasite · Perkinsus beihaiensis · Brazilian Perkinsus sp. · Indian subcontinent Resale or republication not permitted without written consent of the publisherDis Aquat Org 98: [209][210][211][212][213][214][215][216][217][218][219][220] 2012 zoospore. Transmission of Perkinsus spp. does not require an intermediate host. In moribund hosts or when cultured in Ray's fluid thioglycollate medium (RFTM), the mature trophozoites transform into hypnospores. In sea water, these hypnospores develop into zoosporangia, undergo zoosporulation and produce infective zoospores. Trophozoites and hypnospores are also infective .Since the introduction of molecular techniques in disease diagnosis, new species belonging to the genus Perkinsus have been described from various molluscan hosts across the world (Dungan & Reece 2006, Moss et al. 2008. Through culture in RFTM, the standard diagnostic method for Perkinsus spp., the parasites can be identified up to the genus level. The broad host range and highly variable and overlapping morphologic and morphometric features of these parasites makes their species-level identification difficult (Goggin & Lester 1995, Perkins 1996, Coss et al. 2001. ...

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A detailed pathological survey was carried out on the commercially important edible oyster, Crassostrea madrasensis (Preston), from two distinct coastal/brackish water ecosystems of south India. Samples were collected twice a year during wet and dry seasons from 2009 to 2012. Bacterial colonies in the form of prokaryotic inclusions, protozoans (Perkinsus beihaiensis, Nematopsis sp. and ciliates Sphenophrya sp. and Stegotricha sp.), metazoans (trematodes, turbellaria, cestodes and crustaceans) and shell parasites (Polydora spp. and Cliona spp.) along with various pathological conditions (digestive tubule atrophy, ceroid bodies, haemocytic infiltration, tissue necrosis and neoplastic disorders) were observed in C. madrasensis collected from two sites. Intensity, spatial and seasonal variations in infection prevalence and pathological effects on the host were studied. The protozoan parasite, P. beihaiensis; shell parasite, Polydora spp. and pathological condition, digestive gland atrophy were most prevalent in occurrence. High-intensity infections with P. beihaiensis, larval trematodes and Polydora spp. were found to cause significant impact on host physiology. All other parasites were observed with low mean prevalence and intensity. Karapad in Tuticorin bay, the site reported with marked pollution levels, exhibited higher number of parasitic taxa and high mean prevalence and intensity for pathological conditions.