First report of nematode parasite, Camallanus cotti (Camallanidae) (Fujita, 1927) in Barilius bola (Cyprinidae) (Hamilton 1822), from Jaldhaka river of North Bengal, West Bengal.

In the present study the parasitic nematode, Camallanus cotti (Camallanidae) was identified for the first time in a new host fish, Barilius bola (Cyprinidae), from the Jaldhaka river in North Bengal, the northern part of West Bengal, India, during the period from January 2023 to December 2023. The parasite infected the gastrointestinal region and was protruding from the anal opening, showing excessive mucus secretion in the anal region of its host. Sixty-six (58.41%) out of 113 medium-sized fish were infected. Marked variations in the prevalence, mean intensity, and relative abundance were observed in the summer. These variations might be due to the environmental conditions during different seasons and the presence of an intermediate host for this parasite. Worms were described morphologically and morphometrically by light microscopy and scanning electron microscopy (SEM). Previously identified novel characters were confirmed and reassessed. More studies are required to determine the internal problems of the fish and the impact, establishment and spread of this parasite.