Fish "chemistry" question...

MatsP · Post by **MatsP** » 23 Mar 2005, 10:12

I've read several places that fish release ammonia through their gills. My question is: Is it really ammonia, or urea that is released by the fish?

Urea, chemical formula (NH2)2CO, is what human urine[1] contains to release excess nitrogen from proteins, and it breaks down to ammonia pretty easily under the right circumstances...

[1] And just about any other animal that I'm aware of releasing something like urine.

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Mats

Post by **Silurus** » 23 Mar 2005, 10:28

It's ammonia. Humans (and all mammals) excrete urea as the nitrogenous waste because it uses less water. Ammonia is the initial waste product, but to excrete it requires a lot of water, and desiccation is always a prime evolutionary concern for terrestrial animals (this is obviously not a problem for fish). For the same reason, arthropods, reptiles and birds excrete nitrogenous wastes in the form of uric acid.

MatsP · Post by **MatsP** » 23 Mar 2005, 10:41

Thanks for the explanation. I should have realised that it's got to do with the fact that fish live in water, shouldn't I...

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Mats