Morphologic and Genetic Evidence for Mixed Infection with Two Myxobolus Species (Myxozoa: Myxobolidae) in Gray Mullets, Mugil cephalus, from Korean Waters

The present study was performed to trace the decisive evidence for mixed infection of 2 Myxobolus species, M. episquamalis and Myxobolus sp., in the gray mullet, Mugil cephalus, from Korean waters. Mullets with whitish cyst-like plasmodia on their scales were collected near a sewage plant in Yeosu, southern part of Korea, in 2009. The cysts were mainly located on scales and also found in the intestine. The spores from scales were oval in a frontal view, tapering anteriorly to a blunt apex, and measured $7.2{\mu}m$ (5.8-8.0) in length and $5.3{\mu}m$ (4.7-6.1) in width. Two polar capsules were pyriform and extended over the anterior half of the spore, measuring $3.5{\mu}m$ (2.3-4.8) in length and $2.0{\mu}m$ (1.5-2.2) in width. In contrast, the spores from the intestine were ellipsoidal, $10.4{\mu}m$ (9.0-11.9) in length and $8.4{\mu}m$ (7.3-10.1) in width. The polar capsules were pyriform but did not extend over the anterior half of the spore, $3.7{\mu}m$ (2.5-4.5) in length and $2.2{\mu}m$ (1.8-2.9) in width. The nucleotide sequences of the 18S rDNA gene of the 2 myxosporean spores from scales and intestine showed 88.1% identity to each other and 100% identity with M. episquamalis and 94.5% identity with M. spinacurvatura from mullet, respectively. By the above findings, it is first confirmed that mullets from the Korean water are infected with 2 myxosporean species, M. episquamalis and Myxobolus sp.