Production of high quality gonads in the sea urchin Mesocentrotus nudus (A. Agassiz, 1864) from a barren by feeding on the kelp Saccharina japonica at the late sporophyte stage

Gonad quality (color, texture, and taste) of adult Mesocentrotus nudus from a barren can be improved by feeding with the kelp Saccharina japonica. Fronds of cultivated S. japonica accumulate resources from May or June as they form zoospores (maturation). In this study, the effect of feeding cultivated S. japonica at the late sporophyte stage (May-July) on the gonad quality of M. nudus from a barren and cultured in cages suspended offshore in Shizugawa Bay, Miyagi Prefecture, Japan, was investigated. At the end of the culture period, gonad indices, hardness, color (L*, a*, b*), free amino acid (FAA) content in the gonads, the consistency of these traits among individuals, and sensory scores of the cultured sea urchins (CE) were compared to those of a natural population from a barren (BE), an Eisenia bicyclis bed (EE) (fishing ground), and urchins from the barren at the start of the culture period (BS). The CE group exhibited a higher gonad index and L* value, and lower gonad hardness and variation among individuals than those of the BS group. Sensory evaluation showed that gonad taste and overall quality of the CE group was more desirable than the EE group. The desirable taste is a result of sweetness due to a high alanine content, strong umami, and low arginine content. It is likely that increased gonad size and improved gonad quality and consistency among individuals were due to feeding the urchins with mature, nutritious S. japonica at the late sporophyte stage. Further research is required to identify the nutrient constituents of S. japonica at the late sporophyte stage that affect gonad taste.