Changes in free amino acid concentrations and associated gene expression profiles in the abdominal muscle of kuruma shrimp (Marsupenaeus japonicus) acclimated at different salinities

Shrimps inhabiting coastal waters can survive in a wide range of salinity. However, the molecular mechanisms involved in their acclimation to different environmental salinities have remained largely unknown. In the present study, we acclimated kuruma shrimp (Marsupenaeus japonicus) at 1.7%, 3.4% and 4.0% salinities. After acclimating for 6, 12, 24 and 72 h, we determined free amino acid concentrations in their abdominal muscle, and performed RNA sequencing analysis on this muscle. The concentrations of free amino acids were clearly altered depending on salinity after 24 h of acclimation. Glutamine and alanine concentrations were markedly increased following the increase of salinity. In association with such changes, many genes related to amino acid metabolism changed their expression levels. In particular, the increase of the expression level of the gene encoding glutamate-ammonia ligase, which functions in glutamine metabolism, appeared to be associated with the increased glutamine concentration at high salinity. Furthermore, the increased alanine concentration at high salinity was likely associated with the decrease in the expression levels of the the gene encoding alanine-glyoxylate transaminase. Thus, there is a possibility that changes in the concentration of free amino acids for osmoregulation in kuruma shrimp are regulated by changes in the expression levels of genes related to amino acid metabolism.