Seasonal variation and identification of parasitic fauna of edible ornamental fish investigated by light and electron microscopy with special reference to histopathological tissue alteration of infected organs

This communication deals with seasonal variation of protozoans of edible ornamental fishes of West Bengal, India. During this survey, 1566 edible ornamental fishes were collected from different fish farms, ponds, and nearby markets of several district of West Bengal namely, Nadia, South 24 Parganas, Hooghly, North 24 Parganas, Birbhum, Purba Barddhaman, and Paschim Barddhaman from November 2019 to December 2022. Three ciliate ectoparasites belonging to the genera Trichodina, Trichodinella, and Tripartiella and three myxozoan parasites belonging to the genera Myxobolus, Thelohanellus, and Kudoa have been identified from edible ornamental fish, namely, Anabas testudineus, Bloch, 1792. Our study shows ciliate parasites have a higher rate of infection than myxozoan parasites. The highest prevalence of ectoparasitic infection has been reported during the post-monsoon season, i.e., from November to February, followed by monsoon season while lowest prevalence has been observed during pre-monsoon season, i.e., March to June, implying that environmental variables play a role in the spread of infections. The identification of these ciliates and myxozoans parasites was done by a widely used staining technique, along with an ultrastructural study of the myxozoan parasites using scanning electron microscopy. The current work also reveals the histopathological alterations in the gill and fin of Anabas testudineus, after infection with myxozoan parasites along with an ultrastructural study using scanning electron microscopy, which has not been previously studied. Therefore, this investigation also allows some insight into the previously unrecorded tissue-level alteration of infected host organs due to parasitic infestation.