Abstract

• Cirrhinus mrigala fingerlings were sampled monthly from Yezin Fishery Station, over 12 months of study period and examined for intestinal myxosporean parasites. Three myxosporean species, Myxobolus sp., Thelohanellus sp. and Henneguya species under phylum Cnidarian were recorded. Among all these parasites, the most dominant species was Myxobolus sp., followed by Thelohanellus sp. and Henneguya species. Spores of Myxobolus sp. elongated and ellipsoid in valvular view. It had 11.6µm±1.1µm in length and 7.6µm±0.8µm in width. The myxospores of Thellohanellus sp. were pyriform in shape, blunt at the anterior end measuring 16.0µm±1.3µm x 8.8µm±1.3µm in size. Spores of Henneguya species are oval in shape and measurement of its length and width were 27.5µm±1.7µm x 3.8µm±0.7µm in size. The highest prevalence and intensity of Myxobolus sp. infection were recorded in December 2018 (84%). The highest prevalence and intensity of Thelohanellus sp. infection were found in November (18%). However, Henneugya species was found only in December with low prevalence infection (4%). Cyst formation of Myxobolus sp. was found on the surface of intestine. To examine the histopathological changes of infected tissues, histopathological slides were prepared and checked under microscope. Histopathological changes such as proliferation of villi, necrosis of serosa, mucosa and submucosa as well as space in villi necrosis and fusion of villi were observed in the intestine of infected fish. Therefore, management practices and pond hygiene should be adopted in nursery operation systems and grow-out ponds for producing quality fish fry and successful harvesting.