Light microscopic characterization of camallanid<i> </i>nematode parasitizing <i>Tor putitora</i> (Hamilton, 1822) in Mahakali River, Nepal

Helminth parasites infect a wide variety of fish, with nematodes being widely distributed pathogens, especially in wild fish. The present study aimed to document the morphological characteristics of camallanid nematode infecting the golden mahseer (Tor putitora) fish in the Mahakali River along the Nepal-India border of Kanchanpur district, Nepal. Fish samples (n=157) were collected from Khalla and Bhujela areas in the river and nearby markets from March 2023 to February 2024. As revealed by light microscopy, the morphology of the present nematode species closely resembled the Asian freshwater fish nematode Camallanus cotti Fujita, 1927. Notable features included translucent red color in the fresh specimen, a pale yellow buccal capsule with longitudinal ridges and lateral valves, two amphids, eight cephalic papillae, two sclerotic plates, a basal ring separating the oesophagus from the buccal cavity, prongs of tridents extending beyond the basal ring, inconspicuous nerve ring in the muscular oesophagus, deirids at the beginning of glandular oesophagus, oesophagus with short anterior muscular and long posterior glandular portion, pre equatorial vulva and uterus confined in the posterior part of the body containing first stage larvae in gravid female, long tail and finely striated cuticle. The study, thus, confirmed that the camallanid nematode parasitizing freshwater fish golden mahseer is C. cotti.