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GONAD QUALITY OF THE SEA URCHIN Mesocentrotus nudus FED Saccharina KELP BY OFF-SHORE CAGE CULTURE  

Satomi Takagi*, Yuko Murata, Eri Inomata, Ayaka Horikoshi,
Hikaru Endo, Masakazu N. Aoki, and Yukio Agatsuma
 
Graduate School of Agricultural Science,
Tohoku University
Sendai, Miyagi 981-8555, Japan
satomi.takagi.q2@dc .tohoku.ac.jp

Mesocentrotus nudus is a common sea urchin in northern Japan and is harvested commercially. This species inhabits densely in barrens in subtidal rocky bottoms, although the gonads from barrens is smaller and less marketable than those from kelp beds. The aims of this study is to improve low gonad quality by the short-term cage culture.

Sea urchins were collected from a barren and were cultured in a cage suspended from rope for 3 months from February to June 2014. Sea urchins were fed on the stipes inside of sporophylls and color-faded blades of the kelp Undaria pinnatifida for first 2 months, then, the kelp Saccharina japonica ad libitum every 7−10 days until the end of culture. For 30 specimen harvested from the cage and each 30 specimen from the barren and Eisenia bicyclis kelp bed at the start and the end of the culture, their test diameter, body weight and gonad weight were measured. The gonad color (C.I.E.L*a*b*), gonad firmness, and water content were also examined. Using the values of gonad color, we calculated total color difference (∆Eab*) from that in the kelp bed. The content of free amino acids in each gonad was analyzed. Sensory evaluation of the gonads was carried out by fishermen. The gonad index (gonad weight×100/weight) of cultured sea urchins increased from 6.3 to 15.6, significantly higher than that from the barren. The value of ∆Eab* in the gonad of cultured urchins was lower than that from the barren, indicating improvement of total gonad color. The gonad firmness of the cultured urchins was closer to that from the kelp bed. There was no significant difference in water content in gonad among each treatment, suggesting no relation to gonad firmness. The sweet-tasting amino acids, alanine and serine in the gonads of cultured urchins increased. In contrast, the bitter-tasting amino acids, arginine and lysine decreased significantly. The gonad of the urchins from cage culture and the kelp bed was highly evaluated by fishermen. We presume that extension of feeding duration would increase gonad size and further improve gonad quality.




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