Sporophyll of Undaria pinnatifida: a potential feed for the production of high-quality gonads in the sea urchin Mesocentrotus nudus (A. Agassiz, 1864)

Previous study has shown that feeding fresh Saccharina japonica kelp at the late sporophyte stage to Mesocentrotus nudus from a barren can improve the gonad quality of the sea urchin. In particular, the basal frond portion of S. japonica, which accumulates amino acids during maturation, greatly enhances the sweet and umami taste of the gonads. In the kelp Undaria pinnatifida, resources are accumulated in the blade for growth, then translocated to the sporophyll for maturation at the late sporophyte stage. In this study, we demonstrate the effects of feeding U. pinnatifida sporophyll to M. nudus from a barren from May to July on gonad quality (size, color (L*a*b*), and taste (free amino acids)) compared with the effects of feeding the U. pinnatifida midrib (negative control) and the basal frond portion of S. japonica (positive control). Feeding M. nudus the U. pinnatifida sporophyll, which has high protein, carbohydrate, and total and free alanine contents, improved M. nudus gonad size and color and increased alanine content and decreased arginine content in the gonad, similar to the results of feeding M. nudus the basal frond portion of S. japonica. The sporophyll increased free glutamic acid and decreased bitter-tasting amino acid contents in the gonads of sea urchins, indicating that feeding of the sporophyll improved the gonad taste more than feeding of the basal frond portion of S. japonica. This study first indicated that the sporophyll of U. pinnatifida is a high potential feed to improve gonad taste of M. nudus. The appropriate feeding period in which gonad quality can be improved must be confirmed in order to shorten the duration of M. nudus culture.