Subject: Where do Fish urinate from?

In my country, when someone wants to say "I'll show you who calls the shots 
around here", the phrase he might use is: "I'll show you were the fish 
urinates from". (I don't know what's the origin of this phrase. It might be 
from Yiddish).
Everyone who ever owned an aquarium knows where the fish defecates from. I 
always assumed fish urinate from the same place. However, someone told me it's 
wrong, and that fish extract urine from its gills. Which is the truth? and is 
it the same for all kinds of fish, including sharks?
Are there other animals that urinate from unexpected places?
Thanks in advance
Tally.

Re: Where do Fish urinate from?