Parasitological and histological analysis of a new species of the genus Thalohanellus and description of a myxozoan parasite (Myxosporea: Bivalvulida) from cultured ornamental goldfish, Carassius auratus L.

An ornamental fish parasitological survey of West Bengal, India during the year 2014-16 revealed that goldfish, Carassius auratus, was the most susceptible species for myxozoan infestation. This communication revealed the presence of two myxosporean species belonging to the genera Myxobolus and Thelohanellus. Although myxozoan infestation has been determined by isolating small to large, spherical to ellipsoidal plasmodia up to 0.5-2.5 mm were filled with disporic pansporoblasts and mature spores. M. ichkeulensis and one new species T. dipaki n. sp. have been isolated infecting the ornamental goldfish (Carassius auratus) for the first time in India. In the present study, new host, and new locality for M. ichkeulensis have been reported. The description of M. ichkeulensis is being considered as a first report from India. Spore of T. dipaki n. sp. measures uniquely 13.99 ± 0.60 × 9.82 ± 0.60 μm in size, having a one globular pyriform polar capsule measuring 7.45 ± 0.62 × 5.91 ± 0.39 μm. The severity of newly isolated myxozoan infestation has also been assessed by the histopathological changes of fins of the hostfish. A combination of light and scanning electron microscopic observation along with its severity of infestation, comparison of same and closely related species has been incorporated to identify the new species. The paper deals with the diversity, distribution and taxonomic descriptions of new and known myxozoan species along with new host, locality records and incidence of infestation.