Sublethal Effects of The Toxic Alga Karlodinium Veneficum On Fish

Abstract Dinoflagellates of the genus Karlodinium are ichthyotoxic species that produce karlotoxins. Karlotoxins show hemolytic and cytotoxic activities and have been associated with fish mortality. This study evaluated the effect of toxins released into the environment of Karlodinium veneficum strain K10 (Ebro Delta, NW Mediterranean) on the early stages of Danio rerio (zebrafish). Extracts of supernatant of K10 contained KmTx-10, -11, -12, -13, and a sulfated form of KmTx-10. Total egg mortality was observed for karlotoxins concentration higher than 2.69 µg L−1 and the 1.35 µg L−1, 87% of development anomalies were evidenced (concentrations expressed as KmTx-2 equivalent). Larvae of 8 days post-fertilization exposed to 1.35 µg L−1 presented epithelial damage with 80% of cells in the early apoptotic stage. Our results indicate that supernatants with low concentration of KmTxs produce both lethal and sublethal effects in early fish stages. Moreover, apoptosis was induced at concentrations as low as 0.01 µg L−1. This is of great relevance since detrimental long-term effects due to exposure to low concentrations of these substances could affect wild and cultured fish.