MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF Myxobolus baskai Molnár, Székely, Mohamed & Shaharom - Harrison, 2006 INFECTING THE GILLS OF FINGERLING STRIPED CATFISH (Pangasianodon hypophthalmus) IN CAN THO CITY, VIETNAM

Abstract

During a survey on the occurrence of myxosporean spores (Myxozoan) parasitizing the gills of striped catfish (Pangasianodon hypophthalmus) fingerlings in the Can Tho city area, a total of 100 fish samples were collected from ponds in Trung Nhut ward and the Agricultural Service Center in Vinh Thanh commune, Can Tho city. Morphological observation of fresh wet mount preparations revealed that 25 out of 100 fish were infected with spores of Myxobolus baskai located in the gill tissue. The cysts ranged in size from 0.3 to 0.9 mm and were attached to the gill lamellae. Each cyst contained numerous spores. The mature spores were ovoid in shape when viewed from the frontal plane. The posterior end of the spore was rounded, while the anterior end was tapered and thickened. The average spore dimensions were 14.5 µm in length (range: 13.8 - 15.1 µm), 11.1 µm in width (10.5 - 11.8 µm) and 6.4 µm in thickness (6.2 - 6.9 µm). Each spore possessed two relatively equal, pyriform polar capsules, measuring 6.4 µm in length (6.1 - 6.6 µm) and 3.2 µm in width (3.0 - 3.6 µm). Inside each polar capsule, the polar filament was coiled into 4 to 5 turns. The SSU rDNA gene fragment obtained from the spores was 1,552 base pairs in length. Phylogenetic analysis of the SSU rDNA sequence revealed that M. baskai is genetically closely related to M. eszterbaueri, a species previously reported parasitizing the gills of P. hypophthalmus in Thailand.