What is a Fish?

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Osmoregulation in fishes
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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

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Osmoregulation

• Osmoconformer
• only Hagfish (Myxini)
• Osmoregulators
• Lampreys, elasmobranchs and teleosts
• Stenohaline
• Euryhaline

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Elasmobranch osmoregulation in SW

• 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

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Elasmobranch osmoregulation in SW
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Osmotic gradients in teleosts
High salinity
Low salinity
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FW
SW
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Teleost osmoregulation in SW
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Chloride Cell Saltawater teleost
LocationGill Operculum epithelia
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Chloride Cell Saltawater teleost
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Teleost osmoregulation in FW
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Chloride Cell Freshwater teleost
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• Keep cholride cells
• at all times, even
• when in freshwater

Fundulidae Mummichog Fundulus heteroclitus
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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)