Report of Amyloodinium ocellatum in farmed black scraper (Thamnaconus modestus) in China

Abstract

Black scraper, Thamnaconus modestus is a filefish with high market value but the standing stock has been decreased in the past years due to the overexploiting and environmental fluctuations. Industrial culture of black scraper relieved the tense between supply and demand but at the same time brought some disease problems. In this study, we reported a mass death case of cultured Thamnaconus modestus caused by Amyloodinium ocellatum in China. The disease outbroke at temperature of 22–24 °C and the main clinical symptoms were anoxia, decreased feeding activity, reduced mobility, lost balance and subcutaneous hemorrhage. According to the observation, the trophonts of A. ocellatum were non-transparent, suborbicula and the main parasitized tissues were gill and fin, accompanying with the necrocytosis of gill lamella, and hyperplasia of fin cell. The amplification and sequencing of the ribosomal RNA gene showed the parasite was 97.41–99.92% similar with A. ocellatum. The case that amyloodiniosis only occurred in T. modestu but not in turbot cultured with the same condition, indicated the tolerance of former was lower than the latter and farmers should take more surveillance to avoid the mass fish mortality in temperate season. This is the first report about the occurrence of amyloodiniosis in the black scraper.