Do Fish Pee?

Yes, of course, fish urinate. But not all fish urinate the same way. Freshwater fish must rid themselves of the water that is constanly accumulating in their bodies through osmosis. The kidneys of freshwater fish must produce exuberant amounts of dilute urine to prevent their tissues from becomming waterlogged.
Compared to their freshwater counterparts, marine fish, who lose water through osmosis, produce little urine.
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