Posted by sami on June 2, 2005

Q: why do fish need a larger surface area to extract oxygen from the water then an animal of similar size would need on land?

A: Because there is much less oxygen available to animals living in the water than there is on land. In the air, at sea level, there is about 21% oxygen available to a lizard, for instance, but much less oxygen is present in water (oxygen levels can vary a great deal in water). Therefore, organisms living in water must be much better at "capturing" that oxygen to ensure they have enough for life. Ectotherms (cold-blooded animals) need less oxygen than endotherms (warm-blooded animals) but if you compare a lizard with a fish, the fish must be better at obtaining its oxygen needs than the lizard simply because it is living in an environment that has less oxygen available. I hope this helps. Thanks for you question.

John Wiessinger ( June 2, 2005)