Flathead grey mullet, Mugil cephalus, with mass whitish cystlike plasmodia on their scales were collected at Kerchensky preglass of the Black Sea in 2015. The prevalence of infected fish varied from 15% in spring, reached 100% in summer, and declined to 2.5% in autumn. No fish mortality was detected. The spores were oval in frontal view, tapering to a blunt apex. Two unequal polar capsules were pyriform and extended over the anterior half of spore. Spores were 8.2±0.03 μm (7.9-8.4) long, 5.9±0.23 μm (5.2-7.3) wide, and 4.4±0.17 μm (4.0-4.7) thick. Two pyriform and unequal polar capsules were observed (4.0±0.07 μm (3.3-4.5) long, and 1.5±0.24 μm (1.1-1.8) wide). The investigation of nucleotide sequences of the 18S rDNA gene of the myxosporean spores from scales with universal primer A (5′-ACCTGGTTGATCCTGCCAGT-3′) and B (5′-TGATCCTTCTGCAGGTTCACCTAC-3′) showed 100% identity with episquamalis, and 99 % with M. bizerti, M. ichkeulensis, M. spinacurvata and Myxobolus sp. previously detected in mullets. The results obtained from the present study reveal that M. episquamalis, found on the scales of M. cephalus from Kerchensky preglass of the Black Sea, is new record for Russian waters.
