One of life’s unanswered questions and one I was always curious of being, “Do fish sleep?” They do not have eyelids and always seem to be constantly going. People just assume they do not because they have trouble thinking of a fish laying down to get some rest similar to the way mammals do. It also probably enters the mindset of a few people that fish always has to be protective of themselves just in case certain species are near them that want to use them as prey. Most species need food to survive, for many types it is themselves. Which leads to assumptions that fish are awake on high alert at all times. Well, if you were one of the curious human beings that did assume that, your inference was incorrect.
To finally answer your question, fish do sleep. Not all fish sleep the same, but all species do sleep. It is hard to process since they do not sleep like mammals. Fish take naps and sleep when they get tired, just like mammals. Humans sleep by closing their eyes and looking at their eyelids while a certain brain wave pattern is featured in their neocortex. Fish have neither of those functioning in or on their body so their resting time happens quite differently. When analyzing a fish to know they are sleeping, there are four definitive observations to notice during that period of time. The four consist of inactivity for a long time, a resting posture, a certain period of time each day they do rest, and decreased sensitivity to their environment.
Most fish rest, but some complete the process in different ways Cardiac and respiratory rates are lowered along with less movement occurring in vital places. The mackerel and bluefish have never been spotted sleeping. Both species constantly swim and around night time they happen to swim less and create less movement, but never come to a complete stop. Also, depending on the habitat they live in (yes, they all live in water) such as lower depths or a higher surface can influence the amount of sleep they get. It has been recorded that surface fish sleep four times more than cave fish. All fish are different
Research shows that there is a specific gene in all fish that is either dominant or regressive that determines how long and if they sleep. The proof shows that the cave fish’s gene is dominant, which leads to their shorter need for sleep. The only similarity between a mammal’s rest and a fish’s rest is that they both process and refresh brain functions from sleeping. Fish are different from mammals, but it should be a universal question whether they rest or not. Most of every species need rest, they just receive that sleep in different ordeals.
Sources:
http://www.todayifoundout.com/index.php/2015/03/fish-sleep/
http://thefisheriesblog.com/2014/03/09/do-fish-sleep/
https://sleep.org/articles/do-fish-sleep/
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http://thefisheriesblog.com/2014/03/09/do-fish-sleep/