Improvements to the RTgill-W1 fish gill assay for ichthyotoxins: a comparison of the potency of different toxin fractions and extracts tested with different microplate materials

Different microplate materials were compared for in vitro screening of purified phycotoxins and algal extracts using the fish gill cell line RTgill-Wl. Glass plates coated with collagen I were more suitable for assays with brevetoxin and for methanol extracts of the haptophyte Prymnesium parvum (up to 33% more toxic). By contrast, polystyrene plates showed better results with karlotoxin (19% more toxic), and with extracts from the dinoflagellates Karlodinium veneficum, Karenia mikimotoi and Amphidinium carterae (20- 37% more toxic). Care should also be taken to conduct tests in light or dark conditions when toxins or extracts are light sensitive, as was found with Chattonella, Fibrocapsa and Prymnesium extracts (53-90% difference among results). As a first screening step for unknown toxins the use of both glass and plastic plates is strongly recommended. The differential behaviour of ichthyotoxins in plastic or glass containers and in light and dark conditions also contributes to our understanding on how these compounds can mediate fish kills in nature.