Chandrika M. Liyana-Pathirana

The effect of an artificial diet on the biochemical composition of the gonads of the sea urchin (Strongylocentrotus droebachiensis)

Green sea urchins (Strongylocentrotus droebachiensis), taken from the wild were fed on a grain-based artificial diet over a 9-week period. At intervals, the animals were harvested and the gonads analysed for proximate composition, lipid class distribution, fatty acid and carotenoid pigment compositions. During the feeding period the lipid content decreased and the moisture content increased. Meanwhile, the protein content was highest after 9 weeks of feeding on the artificial diet. Major non-polar lipid classes were triacylglycerol (TAG), free fatty acids (FFA) and sterols (ST) while dominant polar lipid classes were phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The content of PC was much higher than that of PE on week 0. However, PE became dominant on week 9 after feeding on the artificial diet. The fatty acids 14:0 and 16:0 were the major saturated fatty acids (SFA), consistently present in the total, non-polar and polar lipids of sea urchin gonads. Polyunsaturated fatty acid (PUFA) 20:5n-3 (eicosapentaenoic acid, EPA) was the highest on week 0 while 18:2 n-6 became dominant with increased feeding period with a concurrent decrease in the content of 20:5n-3. Further, 20:1n-15 was the major monounsaturated fatty acid (MUFA) at week 0, but its content decreased significantly (P<0.05) after introducing the artificial diet. The total carotenoid content decreased by 50% at the end of the feeding period. Major carotenoids present in sea urchin gonads were echininone and β-carotene. The relative content of echininone was lowest at week 0, but increased when the urchins were fed on the artificial diet with a simultaneous reduction in β-carotene levels. The study demonstrates the importance of feed supply in lipid composition of sea urchin gonads.

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.