Occurrence of Multispecies Myxozoan Parasite Infestation by Genus <i>Thelohanellus</i> Kudo, 1933 in a Group of <i>Labeo rohita </i>(Hamilton, 1822)

Abstract

We describe two Thelohanellus Kudo spp. namely, T. bifurcata (34.94x 8.9μm) on gills and T. caudatus (13x8.9μm) on the caudal and dorsal fins, found infecting Labeo rohita (Hamilton, 1822) fingerlings in a wet lab facility of West Bengal India. The L. rohita fingerlings having spores on fins and gills were segregated and gross pathology was observed for one month. It was done to characterise the morphology of mature spores and to examine the histopathology of infected gills. There were 5-6 white cysts (1-2 mm in length) on the gill filament that were mostly persistent during the one-month study period and infected fish (12.5% prevalent) were listless, anorexic, and emaciated before eventually all of them perished. Spores of 4- 7 mm size in 1-4 numbers were found on caudal and dorsal fins which were visible for two weeks before it gets mature and released, whereas infected fish (20%) were active and underwent normal growth. Additionally, it was discovered that 5% of fingerlings had cysts on their gills and fins. The distal tip of the primary gill lamellae is where the gill epithelium ruptures, releasing the spores. The histological inspection of the infected gill clearly demonstrates infective sporoplasm entry, presporogonic stage, plasmodial maturation, and release of spores. Within a month, it was discovered that 100% of the fingerlings with infected gills died. This is because the plasmodial spores on primary gill filaments damage the structural framework of the gill filament and cause epithelial and vascular cell displacement. Our comparative analysis with previous studies support that orders and families of the parasites are strongly correlated with Thellohanellus Kudo sp: a pathogenic strain of T. bifurcata and a non-pathogenic strain of T. caudatus infecting L. rohita. The spore-forming stages of the gill-damaging T. bifurcata (entry, pre-sporogonic, and sporogonic) are extremely pathogenic to fish fingerlings and cause significant damage to gill tissue