Myxobolus chanosi n. sp., a Novel Myxosporean Infecting Farmed Chanos chanos (Forsskal, 1775) from Alappuzha, Along the Southwest Coast of India

The present study describes a new species of Myxobolus infecting the kidney tissues of farmed Chanos chanos from Alappuzha, Kerala, India. Of the 42 fishes screened, 27 were infected (prevalence 64.28%). The parasites appeared dispersed in the posterior kidney tissues in squash preparations, cysts measuring 56.82 +/- 4.13 mu m x 51.11 +/- 1.40 mu m were observed histologically. Oval, bivalvular spores with smooth shell valves, two unequal and elongate-oval polar capsules, and binucleate sporoplasm place the parasite under the genus Myxobolus. Mature spores measured 11.06 +/- 0.60 x 7.71 +/- 0.74 x 7.62 +/- 0.30 (7.35-8.12) mu m. Unequal, elongate-oval polar capsules with pointed anterior ends were aligned obliquely to the longitudinal spore axis. Large polar capsule occupied two-thirds the spore length, measured 6.61 +/- 0.74 x 4.64 +/- 0.58 mu m; possessed polar filament with four coils, measured 28.05 +/- 0.54 mu m. Small polar capsule, reached half the spore length, measured 3.33 +/- 0.78 x 2.50 +/- 0.41 mu m; with three coils of polar filament, measured 11.81 +/- 0.52 mu m. Vegetative stages ellipsoidal, monosporic and dispersed in kidney tissues. A comparison of the present species with closely related forms showed that it differs morphologically and morphometrically from the others. In BLASTn analysis, the partial SSU rDNA (1239 bp) nucleotide sequence showed close identities with M linzhiensi and Myxobolus sp. SKBU-RC1. In the molecular analysis, it exhibited 4.2% divergence with both M. linzhiensi and Myxobolus sp. SKBU-RC1. Neighbour Joining and Maximum Likelihood trees were topologically similar, and the present species stands out with M. linzhiensi and Myxobolus sp. SKBU-RC1 as sister branches. Gross pathological changes were not apparent in kidneys. However, the fibrous cyst encircling the parasite indicates host immune responses. Based on morphology, morphometry, molecular and phylogenetic analyses, tissue and host specificities along with geographic location, the present parasite is treated as new and is reported here as M. chanosi n. sp. This forms the second report of a myxosporean infection from C. chanos.