Effects of Salinity and Turbidity on the Free Amino Acid Composition in Gill Tissue of the Pacific Oyster, Crassostrea Gigas‪.‬

ABSTRACT Effects of salinity and turbidity stresses on free amino acid (FAA) composition in Crassostrea gigas was investigated using high performance liquid chromatography. Oysters were exposed for 2 to 5 days to low salinity (LS, 7 [per thousand]), normal (control, 30 [per thousand]), high salinity (HS, 39 [per thousand]), and high turbidity in normal salinity (HT, 30 [per thousand], 0.326 g kaolin clay/l). Levels of aspartic acid, glutamic acid, serine, glycine, [beta]-alanine, taurine, and L-alanine in the gill tissues were then monitored using a HPLC. Taurine and glycine were the two major contributors to the total FAA in gill tissues of oysters collected from fields, ranging from 200.7-324.7 and 42.9-69.0 [micro]mol/mg dry tissue. On day 2, total FAA in HS and HT was significantly higher than the levels in the control and LS: taurine and glycine levels in HS and HT were significantly higher than the levels of the controls and LS (P 0.05). In contrast, most FAA levels in LS had dropped except for glutamic acid, glycine, and [beta]-alanine; [beta]-alanine level of oysters in LS on day 2 was about 10-fold higher than the control. Aspartic acid and Glutamic acid levels in HT on day 2 were significantly higher than the level observed in HS. LS and control (P 0.0.5). From day 2 to 5, total FAA in the control increased 11.4% whereas total FAA in HS, LS, and HT decreased 17.3%, 21.6%. and 19.3% respectively. Aspartic acid and glutamic acid levels in the control also increased 29.1% and 50.6% between day 2 and 5 whereas the levels in HS, LS, and HT dropped dramatically, from 47.1 (HT) to 72.0% (LS) in case of aspartic acid and 53.5 (HS) to 68.5% (LS) in glutamic acid. Response of FAA composition in the gill tissues to salinity and turbidity stress was unique in this study, suggesting that FAA analysis is a useful tool to diagnose environmental stress to C. gigas, as was observed in C. virginica. KEY WORDS: free amino acids. Crassostrea gigas, salinity, high turbidity, stress, HPLC, oyster