Abstract

Bloom-forming ichthyotoxic microalgae commonly cause important losses to the Seafood Industry and impact negatively on marine ecosytems. Examples of this kind of microalgae are Heterosigma akashiwo (Raphidophyceae) and Karlodinium veneficum (Dinophyceae). Currrent understanding of the toxicity of H. akashiwo relates it to the production of neurotoxins (e.g. brevetoxins), reactive oxygen species (ROS) or polyunsaturated fatty acids (PUFAS). In the case of K. veneficum, the background indicates the presence of ichthyotoxic toxins (e.g. karlotoxins) with hemolytic, and cytotoxic properties. In this work, the embryotoxic effects of methanolic extracts prepared from biomass pellets of both species on early development stages of zebrafish were studied. Biomass of both species were obtained from cultures carried out in pHcontrolled photobioreactors (12L). Cells were harvested in stationary phase. Zebrafish embryos were exposure to different concentrations of methanolic extract ranging from 50 to 200 mg/L. The embryotoxicity assay was initiated with eggs in the gastrulation phase and it were mounted in 96 well plates with 3 replicates for each concentration. The embryos were observed daily recording the percentage of embryonic mortality (48 hours post fertilization), the percentage of hatching and the presence of larval malformations. For K. veneficum, the average toxicity percentage increased with the concentration of methanolic extract in the well. A maximum of embryonic mortality (>50%) was found at the maximum extract concentration assayed (200mg/L). Although at lower concentrations, the embryonic mortality decreased, sublethal effects on the hatched larvae were observed such as high frequency of malformations. In the case of the Heterosigma extracts, the tendency was similar. However, the magnitude of the effect was lower. Among the most frequent larval malformations observed were caudal torsion, pericardial and yolk sac edema. These results indicate the greatest harmfulness was in Karlodinium veneficum extracts.