ABSTRACT
The osmotic pressure of fish blood is mostly provided by inorganic salts and is approximately one third that of seawater, with marine fish having slightly more salt in their blood than freshwater species. The ionic fluxes for marine fish are approximately an order of magnitude greater than those for freshwater species. This reflects the greater permeability of the marine fish to these ions. Changes in osmoregulation in fish exposed to some stressor have been generally elucidated by measuring the blood plasma (or serum) electrolytes and/or total osmolality. Handling of a fish can, however, cause changes in osmoregulatory parameters independent of environmental pollutants, due to the phenomenon of handling diuresis, and changes in hormonal levels. Cadmium common pollutant appears to cause only moderate alterations in osmotic regulation, but specific ionic regulation, especially that of divalent cations, is quite sensitive to cadmium. Chlorine and Ozone are strong oxidizing agents which are quite toxic to fish.
