Morphological and Molecular Description of a New Species of Myxobolus (Myxosporea: Myxobolidae) Infecting Planiliza Macrolepis (Smith, 1846) From India

The present paper describes a novel species of Myxobolus parasitizing the gill filaments of the largescale mullet, Planiliza macrolepis from Cochin backwaters, Kerala, India. The parasite develops in the gill filaments; plasmodia elongated, milky white, measured 1.37 – 2.18 (1.78 ± 0.35) mm x 0.07-0.12 (0.10 ± 0.02) mm in size. Mature myxospores ovoid in valvular view, biconvex in sutural view with smooth shell valves and measured 6.24 - 7.02 (6.63 ± 0.23) × 5.01 - 6.18 (5.68 ± 0.25) μm in size. Polar capsules equal, oval with pointed anterior ends, 3.07 – 3.58 (3.33 ± 0.12) × 1.68 – 2.42 (2.09 ± 0.18) μm in size. Polar filaments with 4 coils, measured 29.61 ± 4.75 μm in length when extruded. Sporoplasm binucleate with a rudimentary nucleus and a vacuole. A comparison with related Myxobolus species revealed significant morphological & morphometric differences. In BLASTN and genetic distance analysis, the present parasite showed high divergence with other myxosporean sequences, indicating its molecular uniqueness. In Maximum Likelihood and Bayesian Interference analysis, the present species stands out with M. ramadus as sister branch within the Myxobolus clade. In infected gill filaments, the plasmodia caused swelling/deformation, compression of lamellae and reduction in respiratory surface area. Three of 222 P. macrolepis screened were infected, indicating a prevalence of 1.3%. Considering the morphological, morphometric, molecular and phylogenetic differences with the previously described species of myxosporeans, along with the dissimilarities in host and geographical locations, the present parasite is treated as a new species and the name Myxobolus cochinensis n. sp. is proposed.

First molecular evidence of Thelohanellus wallagoi Sarkar, 1985 (Myxozoa) from economically important food fish, freshwater shark Wallago attu (Siluridae) in India

The freshwater shark Wallago attu (Bl. and Schn.) is a frequent silurid in the River Ganga and one of the most commercially exploit fish in India. In a survey on its infection with myxosporeans, spore type belongs to Thelohanellus species was found in the gills, kidney and intestine respectively. Through morphological and molecular investigations, we identified the spore as Thelohanellus wallagoi Sarkar, 1985. They were pyriform in valvular view and slim in sutural view, and had one pyriform polar capsule with four to five turns. The spores measured 8.0 × 4.0 × 2.3 μm. T. wallagoi developed in small cysts in the gill lamellae, whereas cyst and scattered spores of T. wallagoi were also found in the kidney and intestine respectively. The 18S rDNA sequence of T. wallagoi isolates recovered from gills, kidney and intestine were found similar to each other and differed from any other Thelohanellus species available in GenBank and validated its status after 32 years of original description. Phylogenetic analysis signified that T. wallagoi was placed sister to Myxobolus species in the clade that indicated the polyphyletic nature of the genus Thelohanellus.