Accumulation of a bitter amino acid, pulcherrimine, in sea urchin ovaries and its relevance to the annual reproductive cycle

Hemicentrotus pulcherrimus in the Tohoku area is not utilized as a fishery product because the ovaries have a bitter taste almost all year. To discover the cause, we compared the annual reproductive cycles and ovarian accumulation of a bitter amino acid, pulcherrimine, in H. pulcherrimus collected at Mikuni (Fukui Prefecture), where it is fished in summer, and Iwaki (Fukushima Prefecture), where it is not utilized. At both sites, pulcherrimine increased in maturing ovaries as oogenesis proceeded from autumn to winter, decreased after spawning in spring, but remained in spent and immature ovaries for a few months. In Mikuni, pulcherrimine was scarcely detected in the ovaries for several months in summer. However, in Iwaki, late spawning delayed the disappearance of pulcherrimine in summer, and early initiation of oogenesis advanced the restart of pulcherrimine accumulation in autumn compared to Mikuni. Consequently, the period when the ovaries were palatable because of the absence of pulcherrimine during summer was short in Iwaki. The major cause of such short-term palatability could be the lower seawater temperature in the Tohoku area. Furthermore, pulcherrimine was never detected in other sea urchins, although a bitter taste was found in the mature ovaries of some species.