5 Fascinating Fish Facts: Do They Sleep, Do They Wee And Other Fun Questions

How Many Of These Fish Facts Do You Know?

Whether you are a pet fish owner or fly-fishing enthusiast, I am sure you'll find them interesting.

Fish Fact #1: Do Fish Sleep?

Yes and no. Most saltwater fish (as well as freshwater fish) do not have eyelids, so technically they cannot close their eyes to sleep.

They do however rest in different ways: many eat and swim during the day and remain inactive at night, while some are always semi-resting (daydreaming) as they virtually spend their whole lives motionless.

Fish Fact #2: Do Fish Wee?

Yes! Similar to humans, fish have an internal organ called kidney to help filter the nitrogenous waste in the blood, to be passed out as urine. Some of the urine is also diffused through the gills.

Fish's kidney has an extra function: to regular the amount of water in its body. In nature, water tends to flow from a less salty environment to a more salty one in a process called Osmosis.

For saltwater fish, since its body is less salty than salt water, its body tends to lose water to the surroundings through Osmosis. The fish's kidney has to work hard to return as much water to the body as possible.

On the other hand, freshwater fish's body is more salty than the surroundings and it tends to absorb too much water. Its kidney has to pump out as much water as possible.

Isn't it interesting that saltwater fish wee little, while freshwater fish wee a lot?

Fish Fact #3: Do Fish Have Ears?

Fish actually have ears (ear-holes) in their heads, but they do not function very well. Instead, they "hear" from a line of sensitive receptors located on both sides of the body. Fish are able to detect water current and vibration in the surroundings, including the motion of fish and other creatures nearby.

By the way, most fish have very good sense organ and their eye-sight is as good as humans.

Fish Fact #4: Can Fish Swim Backwards?

Most can't, because their fins are not designed to "paddle" backwards. Exception includes fishes in the eel family.

Fish Fact #5: How Can A Fish Stay in Water Instead Of Floating Like Us?

Unlike human beings, fish's body tissue is actually denser than water, so fish don't (and can't) float like us. However, their bodies have to do something to avoid the opposite -- sinking into the deep waters!

This is achieved by an unique organ called swim bladder, which contains gas and regulate its level such that the density of the overall fish is similar to the density of water. Therefore, if the swim bladder does not function properly, the fish cannot swim, may lose its balance and even turn upside down.

I Hope You Enjoyed These Fish Facts

So next time, in addition to showing off your fish, remember to brag out your new found knowledge as well!

* Photograph courtesy of laszlo-photo @ flickr