Toxicity and lethal cell density of the harmful flagellate Chattonella ovata (Raphidophyceae) to yellowtail Seriola quinqueradiata
摘要
We investigated the toxicity and lethal cell density of Chattonella ovata in relation to the mass mortality of yellowtail Seriola quinqueradiata. Two bioassays for juvenile yellowtail were performed using three C. ovata and one C. marina culture strain. In addition, plankton survey data collected from aquaculture farms in the Seto Inland Sea, Japan were analyzed. The lethal times of juvenile yellowtails for all C. ovata culture strains were significantly longer than those of C. marina. Juvenile yellowtail died faster when the cell density of C. ovata cultures increased. In aquaculture farms, the cell density of C. ovata was 106–261 cells mL−1 when the mass mortality of yellowtail was observed, whereas no mass mortality was observed in C. ovata of at least several tens of cells mL−1. It was concluded that the toxicity of C. ovata was weaker than that of C. marina used in this study’s culture strains. The cell density of C. ovata, which potentially causes mass mortality of yellowtail in aquaculture farms, is several hundred cells mL−1. Considering the measures that should be implemented with a precautionary approach, we propose that stop-feeding criteria for C. ovata to yellowtail should be established at 10 cells mL−1.