Body Fluids of Marine Teleost

The body fluids of marine teleost are hypotonic to seawater, so these fishes lose water to the environment especially across the gill epithelium. To replace the lost volume of water they drink seawater.

Figure: chloride cells

The ingested seawater along with NaCl and KCl is absorbed across the intestinal epithelium, 70 to 80% of it enters the bloodstream. Most of the divalent ions iuch as ca²⁺, Mg²⁺ and SO^2-₄ are expelled through the anus. The excess salt absorbed along with the water is subsequently eliminated from the blood by active transport of Na⁺ and Cl^- and perhaps K⁺ across the gill epithelium- the seawater. Divalent salts are also secreted by the kidneys. Gills have special type of secretory epithelium known as chloride cells. These cells actively secrete chloride and probably sodium also into the seawater.