Myxobolus nanokiensis sp. nov. (Myxozoa: Bivalvulidae), a new pathogenic myxosporean parasite causing haemorrhagic gill disease in cultured Indian major carp fish, Labeo rohita (Hamilton 1822) in Punjab, India.

The plasmodia of Myxobolus nanokiensis sp. nov. were found infecting gills of Labeo rohita (Hamilton 1822) The infection rate was found to be 36.67 % (30 fishes were examined and 11 fishes were infected) in the Nanoki pond in Patiala district Punjab. Numerous minute plasmodia each filled with 150-200 spores were detected. Smear of scrapped blood-tinged mucous from gills exhibited millions of spores. Histological sections also indicated numerous plasmodia measuring 38.33-40.33 μm in diameter in the blood vessels of gill filaments. Spores of M. nanokiensis sp. nov. were elongate pyriform in shape and morphologically unique in having sharply pointed beak-like anterior end. Spores measured 9.28 μm × 5.71 μm in size. Polar capsules were equal, pyriform, 5.71 × 2.73 μm in size, each having polar filament with 7-9 coils. The present species has been proposed as new on the basis of its peculiar shape and morphometrics. This is the first report of any myxobolid infection in the farmland fishes in Punjab (India). The plasmodia in the gill filaments were of intralamellar vascular type (LV) and were present within the entire length of the filament. These plasmodia caused hemorrhage, necrosis of the blood vessels and cellular infiltration.