Your cart
There are no more items in your cart
Ever wondered how fish sleep ?
Ever looked at fish and wondered do they ever sleep since they always seem to have their eyes open! Unlike humans and other mammals, water dwelling fish don’t have eyelids so it’s difficult to tell whether they sleep by simply looking at them, however, if you observe fish and watch them for a long time you’ll find that there are periods where they stop swimming around. It will become clear from observing their behavior that fish DO sleep and need rest just like us humans.
A study by researchers at the University of Zurich looked at the sleep of many animals and found that all animals including fish sleep however, sleeping methods vary across species. It’s clear that like humans, fish need time to let their bodies rest and repair but how exactly do fish sleep if they don’t have eyelids to close?
How do fish sleep?
Fish don’t show the usual signs of sleep that a mammal does such as REM (rapid eye movements) and closing of the eyelids (since they don’t have any), instead, they have a very interesting manner of sleeping to most other animals, they become inactive. This can be described as a daydreaming like state where they hover in one place whilst their gills continue to move to keep oxygen flowing through their body just like a humans heart continues to pump.
Whilst sleeping, fish still have to remain alert to danger around them to escape predators. Different species of fish use different methods of protection whilst sleeping. Some coral reef fish lodge themselves between coral reefs, others camouflage themselves between the reefs whereas some bury themselves partially in the sea bed. Interestingly, the crafty parrot fish creates a cocoon of vile mucus around its whole body when sleeping to deter predators away.
The mains signs used to spot whether a fish is sleeping is:
1) Extended Inactivity
2) Reduced sensitivity to stimuli around them – for example if you feed them in a tank they will react to the food slower than usual
3) Slower movements
It’s clearly evident that fish sleep in a very different manner to humans but when do they sleep?
When do fish sleep?
Many fish are Diurnal like humans meaning they are active in the day and sleep at night which is why fishes in aquariums and tanks sleep when the lights are turned off. However, some species of fish are nocturnal, they sleep during the day and are active at night and some don’t sleep until they’re adults or they take breaks from sleeping when they have young or are migrating. It all really depends of the species of fish and the environment they’re in. Unlike humans who follow a circadian rhythm for sleep, fish adjust sleeping patterns according to their environment such as water temperature, light, migration and the availability of food however, they’re still affected by sleep deprivation. Interestingly a study on Zebra fish displayed that some fish can suffer sleep deprivation and become less alert when they have not slept.
As the study of animal behavior continues, it’s evident that fish, albeit their differences have their similarities to humans. So if you have fish at home, don’t forget to put on a timed light in their tank and close the curtains so they know it’s bed time.