Fenton reaction as a possible stimulus to induce spawning in Ezo abalone Haliotis discus hannai during stormy weather

Abstract

Synchronous spawning is an important behavior which increases fertilization success of invertebrates with external fertilization. Previous work has shown that free radicals can induce spawning behavior in tank experiments, but the stimulus for spawning in the wild is not fully understood. Ezo abalone Haliotis discus hannai mainly spawn during stormy weather. Rainwater contains H2O2 and iron (II) ions (Fe2+). We propose that during stormy weather, water layers in the ocean are mixed and the surface layer containing H2O2 and Fe2+ interacts with the ocean bottom; this leads to conditions suitable for the occurrence of the Fenton reaction (wherein Fe2+ ions are oxidized to iron [III] ions by H2O2, and ·OH and hydroxide ions are generated). Hydroxyl radicals (·OH) are generated during the oxidization of Fe2+ by H2O2, and we hypothesized that these induce spawning behavior of abalone in the wild. We observed that H. discus hannai released eggs after salinity decreased as a result of rainfall during stormy conditions. In addition, a tank experiment demonstrated that ·OH generated by the Fenton reaction induced synchronous spawning behavior between the sexes. This study provides a new hypothesis about control of synchronous spawning in H. discus hannai, and the results might be applicable to other invertebrates.