Osmosis and Fish

• Marine Bony Fish (saltwater)

  Adaptations:

  • to replace the water they lose, they drink sea water
  • small glomeruli - low filtration rate, high level of reabsorption in kidneys
  • excrete low volumes of highly concentrated urine
  • active transport of salts from salt-secreting cells in gills to seawater
  • impermeable body cover

  Problems:

  • surroundings are hypertonic to their cells
  • lose water via osmosis
  • gains too many salts via drinking sea water and eating
• Freshwater Fish

  Problems:

  • surroundings are hypotonic to their cells
  • gains too much water via osmosis
  • loses too many salts via diffusion and urine

  Adaptations:

  • impermeable body covering
  • doesn't drink water
  • low level of reabsorption in kidneys
  • excrete high volumes of dilute urine
  • gains salt from eating food
  • active uptake of salts from seawater across gills