Outbreak of gill henneguyosis in pond-cultured Oxyeleotris spp. (Eleotridae, Perciformes) caused by Henneguya shaharini Shariff, 1982 (Myxosporea: Bivalvulida) in south China

Henneguya shaharini Shariff is reported for the first time and found to be the possible cause of high rates of mortality in pond-reared marble goby, Oxyeleotris marmoratus Bleeker and Oxyeleotris lineolata Steindachner and the hybrid species of O. marmoratus (♀) ˟ O. lineolata (♂) in multiple major production areas of south China which expands the geographical distribution and host range of this parasite. This episode of epizootic gill henneguyosis had a distinct seasonal pattern which generally occurred from late December to middle May when water temperature ranged from 13 to 22 °C, but no significantly geographical bias was found. No remarkable clinical symptoms were found in affected fish with the early onset of disease. The severely infected fish, however, swam lonely and listlessly at the water surface and the gill filaments of moribund fish had much smudge attached. Upon necropsy, large amounts of myxosporean plasmodia of variable size could be found in the gill filaments. Histopathological investigations showed that the plasmodia were generally intralamellar, but rarely interlamellar and no distinct inflammatory responses surrounding the intact plasmodia were observed. The high infection intensity causing the displacement of gill filament by plasmodia and respiratory failure was possibly the main cause of fish mortality. Phylogenetic analysis indicated that H. shaharini clustered with two gill-infecting congeners to form an independent Gobioidei-infecting branch in a freshwater Henneguya cluster within a marine Henneguya-Myxobolus clade. The possible source of H. shaharini in China is discussed.