During the present study, two myxosporean species, M. nanokiensis Kaur et al., (2015) and M. slendrii Kaur and Singh (2010) have been described from the gills of Cirrhinus mrigala Hamilton vern. mrigal and Labeo rohita Hamilton vern. rohu at nursery ponds located in village Fagan majra, District Fatehgarh Sahib, Punjab, India. Earlier, M. nanokiensis were described from L. rohita and M. slendrii from C. mrigala. 40 speciemens of Labeo rohita and 40 specimens of Cirrhinus mrigala were examined from November 2014 to April 2015. Out of which 33 and 21 fishes were infected respectively. The age of the fish was recorded as 2-3 months and length of the fish was 4-4.5 cm. The prevalence rate was more in M. nanokiensis (82.5%) than M. slendrii (52.5%). The histological effects of the pathogen were observed by light microscopy. The plasmodia of M. nanokiensis were located in the fine blood capillaries at the centre of gill lamella and plasmodia of M. slendrii were located located within the arteries at the tip of the gill filaments. M. nanokiensis was highly pathogenic than M. slendrii. The plasmodia of M. nanokiensis were typed in “A” category caused complete necrosis of cellular elements and degeneration of gill lamellae and M. slendrii also in “A” category caused total destruction of the gill filament. The gill plasmodial index (GPI) was 1 for both species.
