Pacific white shrimp, , is one of the most important commercially farmed species worldwide because of its rapid growth and osmoregulatory capacity. Abiotic factors such as freshwater inflow, rainfall, and seasonal variations result in fluctuations in water salinity in various aquaculture environments such as ponds and estuaries. To determine the response of to periodic salinity fluctuations, a 30-day experiment was conducted in the laboratory. In this experiment, two salinity fluctuation amplitudes of 4 (S4 group) and 10 (S10 group) were designed, using constant salinity of 30 (S0 group) as the control. The free amino acids (FAA) content, and the transcript levels of genes related to water, ion channels and FAA metablism were determined. Fluctuations in salinity strongly affected the transcript levels of genes related to ion and water channels. With increasing amplitude of salinity fluctuations, the transcript levels of genes encoding Na⁺/K⁺-ATPase α and β, carbonic anhydrase, and V-H⁺-ATPase 1 significantly increased, while the transcript levels of the gene encoding aquaporin 4 significantly decreased (+-ATPase 1 and the Na⁺/H⁺ exchanger were in the S4 group (<0.05). The transcript level of the gene encoding chloride channel protein did not differ significantly among the three groups (>0.05). However, the FAA total content in the gill was significantly increased by increasing salinity fluctuations (<0.05). Compared with the control shrimps (salinity of 30; S0 group), those in the S10 group showed significantly increased transcript levels of the gene encoding alanine transaminase, and significantly decreased transcript levels of the genes encoding aminomethyltransferase and proline dehydrogenase ( generates an active response to salinity fluctuations at the transcriptional level. With the increasing amplitude of salinity fluctuations, the osmoregulation capacity can increase. These results provide a scientific reference for further research on the osmoregulation of shrimps in stressful environments and also for the regulation of water quality in aquaculture.