Ionic regulation in fish: the influence of acclimation temperature on plasma composition and apparent set points

1. Published data on the influence of acclimation temperature on normal ionic concentrations in fish plasma are summarized. 2. Although osmolality rises near 0°C in many marine fish, there is otherwise no general tendency in marine species for osmolality, Na and Cl to fall with increasing temperature. 3. The suggestion that osmolality, Na and Cl in freshwater fish typically fall with decreasing temperature is not supported. 4. K and Ca generally rise with increasing temperature, or stay constant. 5. Mg generally falls with increasing temperature, or stays constant. 6. Evidence on concomitant variations in set points is sparse, but apparent set points for osmolality/Na/Cl, except near 0°C, usually vary by less than ±2%°C−1