Lethal freezing temperatures of Arctic char and other salmonids in the presence of ice

The lethal freezing temperatures of seawater acclimated Arctic char ( Salvelinus alpinus), brook trout ( Salvelinus fontinalis), Atlantic salmon ( Salmo salar), brown trout ( Salmo trutta) and rainbow trout ( Salmo gairdneri) were determined in the presence of ice. Arctic char showed the greatest resistance to freezing (−0.99°C) followed by brook (−0.87°C) and brown trout (−0.81°C) and by salmon (−0.76°C) and rainbow trout (−0.75°C). Plasma electrolyte levels accounted for 90–95% of the observed freezing temperature values. However, the lethal freezing temperatures of all of the salmonids were significantly lower than their plasma freezing temperatures, suggesting that at least one other factor was involved in preventing the fish from freezing. This difference between fish freezing temperature and plasma freezing temperature was greatest in Arctic char (0.2°C) and accounted for 70% of the difference in freezing resistance between char and salmon. It is hypothesized that the char's epidermis acts as a barrier to prevent ice propagation.