Physiological Performance of Anadromous Masu Salmon (Oncorhynchus masou) in Relation to Salinity

Salinity is a key environmental survival factor for all aquatic organisms, especially migratory species. The masu salmon (Oncorhynchus masou) is a representative migratory fish species. Following the freshwater parr stage, anadromous masu salmon briefly inhabit brackish water and transition before migrating to the ocean. To demonstrate the physiological responses of masu salmon (length: 8 ± 0.5 cm, water temperature: 10 ± 0.5 °C) to variations in salinity, we carried out three gradual transfer experiments (gradual daily increases direct transfer experiment of 3.2 (D10), 1.6 (D20), and 1.1 (D30) ppt until reaching 32 ppt) and one (immediate transfer to 32 ppt on day 0) as domestication regimens for masu salmon. The results indicated the following: (1) In the gradual transfer experiment group, growth performance, along with ion and hormone indicators, suggested that the D30 treatment group of anadromous masu salmon exhibited a high level of adaptability. (2) In the direct transfer experiment, in addition to the activity of antioxidant enzymes, both ion concentrations and hormone indicators returned to a stable state within 7 days. Our findings provide a scientific protocol for salinity regulation during the artificial propagation of masu salmon and establish critical acclimation parameters for land-based recirculating aquaculture systems aimed at marine salmonid farming, thereby highlighting their practical value.