Effect of season and artificial diet on amino acids and nucleic acids in gonads of green sea urchin Strongylocentrotus droebachiensis

The content of total and free amino acids (FAA) in green sea urchin (Strongylocentrotus droebachiensis) gonads varied with the season and feeding on an artificial diet. Glycine was the dominant amino acid in each season contributing 12.9-16.6% to the total amino acid (TAA) content, peaking in the spring. In the FAA profile, glycine accounted for 30.3-61.4% in different seasons. A grain-based artificial diet had noticeable effects on the total and FAA compositions of S. droebachiensis. Although, glycine was the dominant amino acid in the TAA profile during early harvesting, tyrosine in gonads became more dominant on week 9 of feeding. Furthermore, glycine was the dominant amino acid in the FAA pool after feeding the artificial diet. The total FAA content in the gonads increased significantly (P<0.05) from 20.6 on week 0 to 180.6 mg/g dry mass tissue on week 3. There were no significant (P<0.05) changes between week 6 and week 9. Deoxyribonucleic acid (DNA) content exceeded that of ribonucleic acid (RNA) in each season, while in cultured urchins, RNA content exceeded that of DNA only on week 6. The RNA/DNA ratio was significantly increased in the summer, whereas this ratio was increased up to week 6 followed by a decrease on week 9 in cultured counterparts.