Do Fish Sleep? - Eduauraa

Every living organism of any species needs rest for proper functioning.

However, throughout the animal kingdom, the form of rest or sleep looks very different compared to one another.

For instance, African elephants sometimes sleep only 2 hours a day while human babies can sleep for 18 hours within a day.

Scientists are continuously studying the sleep cycle of all the known living organisms, and the species that have attracted them the most are the fishes.

With more than 32000 species of fish found at the moment, scientists are continuously monitoring the biology and behaviour of these aquatic creatures.

Sleeping of Fishes

Sleep habit is to consider a two-way approach- a behavioural approach and a brain activity approach.

a. Behaviour

According to behavioural studies, sleep can be defined as a reversible state of reduced responsiveness, which is associated with a lack of body movements.

Moreover, sleep rebound signifies the tendency to sleep for longer after a time of sleeplessness.

This is another behavioural sign of sleeping which different fishes make.

b. Brain activity 

In general terms, sleep is the rest given to the brain. Hence, concerning Brain functionalities, sleep can be quantified through distinct changes in the brain's electrical activity.

However, this sleep measurement through brain activity has been measured only in birds, reptiles, and mammals.

Concerning these approaches and trying to understand the sleeping habits of fish, several challenges are coming in front of the researcher.

First of all, measuring brain waves underwater is difficult. Another issue is the missing neocortex.

It is a part of the brain used for measuring brain waves in humans.

However, it is missing inside the fish.

Hence, some researchers term the sleep-like activity in fishes as rest due to the inability to record the brain waves to understand the signs of sleeping.
 

Reason for sleeping in fishes

There are several hypotheses regarding the need for sleep within living organisms such as humans, fishes or other creatures.

These hypotheses can be divided into primary 2 two sectors – adaptive and restorative.

a. Adaptive

This hypothesis theorizes that sleeping lets animals adapt faster to their environment.

There are also suggestions that sleeping has evolved to assist animals in preventing predators and surviving all day.

b. Restorative

The restorative sleep hypothesis focuses on the need for sleep as a means of repairing.

These theories suggest that the body repairs continuously in sleep mode, successfully processes new memories and data, and improves the immune system.
 

Ways in which Fishes Sleep

Even though sleep is an essential process of living beings, the difference lies in the timing and the amount of sleep.

Therefore, the timing of a fish's sleep and quantity depends on its diet, anatomy, and surroundings.

There are several examples where different fish species exhibit different sleeping patterns.

1. Sharks

The habitat of sharks varies greatly throughout the ocean floors.

The different groups of sharks can live in salty oceans or freshwater rivers.

Interestingly, a saltwater shark species called nurse shark rests during the day, and it responds very slowly when disturbed.

2. Zebrafish

Zebra fishes are freshwater organisms that are mainly used for medical purposes.

However, they sleep at night just like Humana, and they breathe slowly and stop swimming at that time.

3. Mexican Cavefish

Also known as Mexican tetra, Mexican cavefish live in two kinds of environments- caves and rivers.

Scientists have reported that cave fishes have evolved according to their distinct environment and have lost their eyesight.

As a result, this has decreased their requirement for sleep when they are starving.

Places of Sleeping for Fishes

Fishes mostly live in water, and it covers more than 70% of the Earth's surface. Therefore, fishes sleep in different places as well as in different ways.

1. Floating

Certain space species don't swim while they are asleep.

Examples are buccal pumping sharks and Port Jackson sharks.

They breathe using their mouths and push water through the gills.

Another example is the nurse hound shark species that sleeps with eyelids half-closed.

2. Sleep while swimming

Several fish species need a continuous supply of oxygen-rich water through their gills.

For example, some damselfish increases their speed of fin movement while resting.

3. Resting in sand or corals

Fishes sometimes use their environment for defence while sleeping. Lemon sharks rest in a dormant state on the sandy ocean floor for a long time.

Similarly, parrotfish look for a protected place on coral reefs before resting, and once found, use their mucus to make a cocoon-like structure for protection.

Therefore, this is some interesting information about the sleeping habits of fish.

Scientists are continuously trying to learn more about these habits and have concluded that fishes need rest like humans and other animal species.