A NEW MICROSPORIDIAN PARASITE, Microgemma boleophthalmi sp. nov. CAUSING HEPATIC MICROSPORIDIOSIS OF BRACKISH WATER FISH, MUDSKIPPER Boleophthalmus dussumieri (VALENCIENNES, 1837)

Microsporidians are obligate intracellular parasites that infect both vertebrates and invertebrates. The pathogenic potential of microsporidians in fishes has not yet studied for most of the wild fishes. Mudskippers (Family: Gobiidae) are one of the largest groups of amphibious teleosts. They have a significant role in benthic ecology and recognized as potential bio-indicators  of ecosystem. However, studies on the parasites infecting the mudskippers are scanty.

With this back ground, the present study was carried out to identify and characterize the microsporidian parasites infecting mudskipper Boleophthalmus dussumieri, using light and scanning electron microscopy, histopathology and molecular methods.

B. dussumieri collected from Mumbai, Maharashtra, India showed a microsporidian infection in the liver with a low prevalence (11.6%). Large whitish cysts (xenomas) of 0.3-0.5 mm were observed in the liver of fish (Fig. 1). The cysts enclosed pyriform spore measuring  2.9-3.77 X 1.85-2.67 µm and it was similar to the species of genus Microgemma (Fig. 2). Histological observations of infected liver revealed distinct xenoma of the microsporidian. Scanning electron microscopy of the infected liver showed a distinct groove on the anterior end of the spore for polar tube extrusion. The partial 18S rRNA sequence (~1000bp) of the microporidian showed an average of 1.8% genetic divergence with other reported species of Microgemma.

Based on the morphological, histological and molecular sequence information, the hepatic microsporidian was found to be a new species and named as Microgemma boleophthalmi sp. nov. after the generic name of the host. This is the first description of a microsporidian from B. dussumieri and also the first report of the genus Microgemma from India.