Do fish swallow water when they eat?

[Jack Lambert]

Just curious.

[BrunswickDawg]

Just curious.

I don't know, but they damn sure can swallow my hooks. Little bastards.

[Martianlander]

Best Answer: All fish swallow water but in different degrees depending on whether it's a saltwater or freshwater fish. All fish swallow water with food. But drinking is something saltwater fish do and freshwater fish don't.

Miscellaneous explanation:
Saltwater fish have to keep water inside to maintain osmotic balance against the salty water outside. They separate the salt from the water for cellular action, but need to keep this activity up or risk all their internal water rushing back outside their body into the sea. Their slime coat helps them resist salt and keep water inside. They even have specialized kidneys that help keep water in and pump salt out in scant concentrated urine.

Freshwater fish are saltier inside than out. They have to fight to keep that salt in and water out, so they don't drink water per se (even though their lips move). Their slime coat keeps water from the lake from rushing into their bodies (called dropsy). They have specialized kidneys that pump water out and conserve salt, so they urinate a lot but it's very dilute.