Research shows that fish can reduce their activity and metabolism while also being aware of dangers. Some types of species don't need to rest. According to a study by Stanford University School of Medicine, fish produce hormones similar to humans that regulate sleep patterns and calibrate internal body clocks. These include blind, cave fish and deep-water species that swim continuously.
While almost all animals sleep, the way they sleep can vary greatly, especially in fish. Researchers were unable to measure the known brain wave patterns that characterize human sleep and the sleep of many other animals in most fish. For this reason, researchers often refer to fish's sleep as rest.
How do you know if a fish is sleeping?
Don't flush the fish down the toilet as it can be harmful to the native fish in your area. These types of pathogens produce gas and because of this gas, the dead body of fish cannot maintain buoyancy and it starts to swim. Fish don't close their eyes — they don't have eyelids, nor do they show signs of REM (Rapid Eye Movement) sleep. In any case, you will need to have your fish examined by a veterinarian if you notice this type of positioning.
You can take steps to know one way or another by checking your fish's vital signs, dealing with dead or dying fish, and considering other issues with fish that only look dead.
How long does a fish sleep?
Most fish also need to keep moving while they sleep so they pass a constant flow of water past their gills to maintain proper oxygen levels in their bodies. Although research is limited so far, studies in zebrafish suggest that they go through two significantly different stages of sleep, which alternate back and forth. Most of these studies use zebrafish and try to understand things like the effects of sleep deprivation (lack of sleep), insomnia (trouble falling asleep), and circadian rhythm (sleep cycles). Some fish species even stop sleeping at certain times in their lives, such as when they are looking after their young or when they are hiking.