1. Osmoregulation in fishes

2. Osmosis The phenomenon of water flow through a semi-permeable membrane that blocks the transport of salts or other solutes through it van't Hoff formula for osmotic pressure: p = cRT –c is the molar solute concentration –R is the gas constant –T is the absolute temperature

3. Osmoregulation Osmoconformer only Hagfish (Myxini) Osmoregulators Lampreys, elasmobranchs and teleosts Stenohaline Euryhaline

4. Accumulation of organic osmolytes (metabolic by-products): –Urea –TMAO (Trimethylamine n-oxide) Protein stabilization properties Achieve a slightly higher osmotic pressure than seawater FW sharks and rays do not accumulate urea/TMAO Elasmobranch osmoregulation in SW

6. Osmotic gradients in teleosts High salinityLow salinity

7. FW SW

8. Teleost osmoregulation in SW

9. Chloride Cell Saltawater teleost Location: Gill & Operculum epithelia

10. Chloride Cell Saltawater teleost

11. Teleost osmoregulation in FW

12. “Chloride” Cell Freshwater teleost

14. Fundulidae Mummichog Fundulus heteroclitus Keep cholride cells at all times, even when in freshwater

16. Salmonidae Atlantic salmon Salmo salar Develop more chloride and accesory cells when migrate to SW (parr-smolt) Degenereration of chloride- accessory cell complexes when returning to FW (adults)