First report of Perkinsus beihaiensis in Crassostrea madrasensis from the Indian subcontinent

Protozoan parasites of the genus Perkinsusare considered important pathogensresponsible for mass mortalities in many wild and farmed bivalve populations. The present studywas initiated to screen populations of the Indian edible oyster Crassostrea madrasensis, a promis-ing candidate for aquaculture along the Indian coasts, for the presence of Perkinsusspp. Thestudy reports the presence of P. beihaiensisfor the first time in C. madrasensispopulations fromthe Indian subcontinent and south Asia. Samples collected from the east and west coasts of Indiawere subjected to Ray’s fluid thioglycollate medium (RFTM) culture and histology which indicatedthe presence of Perkinsusspp. PCR screening of the tissues using specific primers amplified theproduct specific to the genus Perkinsus. The taxonomic affinities of the parasites were determinedby sequencing both internal transcribed spacer (ITS) and actin genes followed by basic localalignment search tool (BLAST) analysis. Analysis based on the ITS sequences showed 98 to 100%identity to Perkinsusspp. (P. beihaiensisand Brazilian Perkinsussp.). The pairwise genetic dis-tance values and phylogenetic analysis confirmed that 2 of the present samples belonged to the P.beihaiensisclade while the other 4 showed close affinities with the Brazilian Perkinsussp. clade.The genetic divergence data, close affinity with the Brazilian Perkinsussp., and co-existence withP. beihaiensisin the same host species in the same habitat show that the remaining 4 samplesexhibit some degree of variation from P. beihaiensis.As expected, the sequencing of actin genesdid not show any divergence among the samples studied. They probably could be intraspecificvariants of P. beihaiensishaving a separate lineage in the process of evolution