Toxicity comparison between Chattonella marina and Karenia brevis using marine medaka (Oryzias melastigma): Evidence against the suspected ichthyotoxins of Chattonella marina

The marine alga Chattonella marina is often associated with massive fish mortality worldwide. Here, we challenge brevetoxins and free fatty acids as the ichthyotoxins of C. marina by comparing the toxicity of C. marina with a brevetoxins-producing alga Karenia brevis as well as their organic solvent extracts using the seawater medaka Oryzias melastigma. Opposite to K. brevis, toxicity of C. marina was highly correlated with its growth rate and exhibited no dose response relationship between cell density and fish mortality. Fish exposed to C. marina developed significant hyperventilation response, but K. brevis induced hypoventilation response in medaka. Moreover, the organic extracts from C. marina showed no toxicity to fish whereas organic extracts from K. brevis showed significantly higher toxicity than the whole K. brevis culture. The toxins produced by C. marina may be protein in nature or small and labile molecular compounds which are not able to be extracted by traditional organic extraction methods.