Osmoregulation in fishes

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

Osmoregulation

• Osmoconformer•only Hagfish (Myxini)

• Osmoregulators•Lampreys, elasmobranchs and

teleosts

• Stenohaline• Euryhaline

• 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

Elasmobranch osmoregulation in SW

Osmotic gradients in teleosts

High salinity Low salinity

FW SW

Teleost osmoregulation in SW

Chloride CellSaltawater teleost

Location:Gill & Operculum epithelia

Chloride CellSaltawater teleost

Teleost osmoregulation in FW

“Chloride” CellFreshwater teleost

FundulidaeMummichogFundulus heteroclitus

•Keep cholride cells at all times, even when in freshwater

SalmonidaeAtlantic salmonSalmo salar

•Develop more chloride and accesory cells when migrate to SW (parr-smolt)

•Degenereration of chloride- accessory cell complexes when returning to FW (adults)