A possible stimulus to induce SPAWNING in Ezo abalone Haliotis discus hannai during a stormy condition: Fenton reaction induces spawning behavior

Synchronous spawning is an important behavior to increase fertilization success of invertebrates with external fertilization. Previous work has shown that it is possible to induce spawning behavior using free radicals 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 Fenton reaction to occur. Hydroxyl radicals ({middle dot}OH) are generated during the oxidization of Fe2+ by H2O2 and we hypothesized these induce spawning behavior of abalone in the wild. This study observed that H. discus hannai released eggs after salinity decreased due to the rainfall during stormy conditions. In addition, our tank experiment demonstrated that {middle dot}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 could be applicable to other invertebrates.