After spending the first few years of life in fresh water, young  Atlantic salmon (Salmo salar) undergo a complex series of physiological changes that allows them to better withstand the high concentration of salts as they migrate to seawater. Young salmon tolerate the salts in the environment through the development of cells, called ionocytes, that secrete sodium and chloride and a specialized enzyme that acts as a pump to transport these electrolytes.

Landlocked salmon, on the other hand, remain in freshwater and it is unknown if, over time, this has resulted in physiological differences compared to salmon that migrate between freshwater and seawater over their lifecycle (anadromous). So, Dr. Stephen McCormick of the US Geological Survey led a team to investigate if there was a difference in expression of the enzymes responsible for salt transport, as well as the underlying hormonal regulation, between the two types of fish.

McCormick and his team brought salmon into the laboratory to monitor their responses to controlled changes in the environment. They found that levels of an enzyme that allows the fish to live in salty environments and the hormones responsible for regulating seawater acclimation, like cortisol and growth hormone, were higher in anadromous salmon than landlocked fish. These findings shed light on the complex physiological changes that occur during sea-going salmon development as well as how these salmon populations have evolved over the last 14,000 years.