Sublethal effect of the toxic dinoflagellate Karlodinium veneficum on early life stages of zebrafish (Danio rerio).

Dinoflagellates of the genus Karlodinium are ichthyotoxic species that produce toxins including karlotoxins and karmitoxins. 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 the supernatant of K10 contained the mono-sulfated KmTx-10, KmTx-11, KmTx-12, KmTx-13, and a di-sulfated form of KmTx-10. Total egg mortality was observed for karlotoxin concentration higher than 2.69 µg L-1. For 1.35 µg L-1, 87% of development anomalies were evidenced (all concentrations were expressed as KmTx-2 equivalent). Larvae of 8 days postfertilization 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.

Physiological Response of Atlantic Salmon (Salmo salar) to Long-Term Exposure to an Anesthetic Obtained from Heterosigma akashiwo.

Despite the invaluable role of anesthetics as a tool for ensuring animal welfare in stressful situations, there is currently a lack of anesthetic drugs that meet the requirements of intensive aquaculture. In response to the growing interest in anesthetic substances of natural origin, this study evaluated the physiological and health impact of an anesthetic based on an extract of the microalga Heterosigma akashiwo on juvenile salmon (Salmo salar) exposed for a period of 72 h. To simulate a condition closer to reality where fish are subjected to stimuli (e.g., transport), the animals were exposed to 50 mg L-1 of algal extract and to physical stress. Functional, physiological, and histological parameters were evaluated in blood and tissues at different sampling periods (0, 24, and 72 h). There was no mortality and the induction and recovery times observed were within the established criteria for anesthetic efficacy. The anesthetic extract did not induce any side effects, such as stress or metabolic damage, indicating that this extract is a viable option for supporting fish welfare during deleterious events. This study provides information to support that the anesthetic extract tested, derived from H. akashiwo, is a promising candidate drug for operations requiring sedation (e.g., Salmonid transport).

Neuro-2a cell-based assay for toxicity equivalency factor - proposal and evaluation in Chilean contaminated shellfish samples.

There are two official PSP detection methods (mouse bioassay and HLPC-FLD) and a number of alternative methods. Ethical considerations have led to regulations being adopted in some countries that limit or prohibit the application of mouse bioassay. Analytical methodologies (e.g. HPLC-FLD or LC-MSMS) have the disadvantages of not being able to detect new toxins or analogues or reflecting the overall toxicity of the sample. In addition, they require highly trained personnel and expensive equipment, which are not always available. In this work, we have evaluated a method based on the Neuro-2a cell-based assay to detect substances that inhibit voltage-dependent sodium channels (Manger's method). We tested PSP standards and natural samples contaminated with PSP. Here we demonstrate that the adapted Manger's method is suitable for calculating Toxicity Equivalency Factors (TEF) for STX-analogues. The method was shown to be useful for screening contaminated natural samples in concentrations above the regulatory limit for these toxins (80 µg STX equivalents/100 g shellfish). We were able to detect PSP in 19 natural mollusc samples from South Chile despite the presence of other marine toxins. These preliminary results suggest that the method could be used as a first step in screening programmes.