Environmental influences on regulation of blood plasma/serum components in teleost fishes: a review

Concentrations of both inorganic and organic blood plasma/serum components of teleost fishes were reviewed in seven habitat/life-history categories. These were: freshwater; inland saline; estuarine and nearshore marine; pelagic and deep-sea; diadromous; southern cold-water; and northern cold-water. Plasma/serum osmolalities were compared among groups acclimated to/living in fresh and in salt water. Contributions of inorganic ions and colligative and non-colligative organic molecules were evaluated including with respect to melting and freezing points, and antifreeze activity of plasma/serum in species from cold marine waters. Possible roles of TMAO in deep-water fishes were reviewed. Discussion also included influences of ambient salinity and temperature on concentrations of plasma/serum components. Seasonal cycles of blood plasma/serum components were discussed, along with antifreeze concentrations in other body fluids and tissues of cold-water fishes. Regulatory patterns of plasma/serum osmolalities were compared among the most euryhaline of teleosts evaluated here. Highest mean values of plasma/serum osmolalities in sea water were seen in southern cold-water and in pelagic and deep-sea fishes. The southern cold-water group also had the lowest plasma/serum freezing points among these groups. Comparisons of mean plasma/serum Na+ and Cl- concentrations among fishes from fresh waters did not differ significantly among groups, but species from cold marine waters showed higher levels than did other groups in marine waters. Plasma/serum osmotic, Na+ and Cl- concentrations of these seven groups of teleosts were compared with those of other fish-like vertebrate groups. Possible impacts of global warming on regulatory responses of plasma/serum components were discussed.