Morphological, histopathological and molecular characterization of Thelohanellus theinensis n. sp. (Cnidaria: Myxosporea) infecting an Indian major carp, Labeo bata in a cold water wetland in Punjab (India).

A myxozoan parasite belonging to the genus Thelohanellus Kudo, 1933 (Myxosporea, Bivalvulida) was isolated from the gill lamellae of Labeo bata (Hamilton, 1822) inhabiting Ranjit Sagar Wetland in Northern parts of Punjab, India. Histopathology of the infected gills indicated lamellar distortion due to the presence of plasmodia. The intensity of infection was recorded to be moderate as indicated by gill plasmodial index (GPI = 2). The plasmodia were microscopic, ovoid, creamish white, 2.0-4.0 mm in diameter containing 300-400 number of myxospores. The myxospores were broadly pyriform in shape, measuring 8.27 × 4.41 µm, having a prominent pore at the anterior end. The polar capsule was pyriform in shape, measuring 4.15 × 4.10 µm, containing a polar filament coiled perpendicular to the longitudinal axis of myxospore body making 6-7 turns. At molecular level, the analysis of 18S rDNA sequence of T. theinensis n. sp. demonstrated maximum homogeneity of 99 % with T. filli (KR340464) as only 2 gaps were found due to the difference of the last 20 base pairs at the 3' end of T. theinensis n. sp. The current study emphasizes the need for caution when dealing with members of species complex.