Effect of salinity change on free amino acid content in Pacific oyster

In order to identify free amino acids (FAA) that are important as intracellular osmolytes in Crassostrea gigas, we investigated the change in FAA content in the mantle exposed to an abrupt decrease or increase in salinity. In hypo-osmotic adaptation, most FAA showed remarkable and synchronous decreases from 2 to 8 h, suggesting that the non-selective efflux of FAA was mainly responsible for the decrease in FAA. Taurine that accounted for approximately 80% of total FAA content contributed most significantly to the hypo-osmotic adaptation. In hyper-osmotic adaptation, significant increases in glycine, alanine, P-alanine, proline, arginine and taurine were observed. Of these, alanine showed an immediate increase that is important to short-term adaptation to hyper-osmolality, while taurine showed a slower and substantial increase that contributes to a long-term adaptation to hyper-osmolality.