Yes, fish do sleep, but the concept of sleep in fish is different from sleep in mammals. Fish do not have the same type of centralized nervous system as mammals, so they do not experience sleep in the same way.
Fish do, however, have periods of rest and reduced activity, during which they can become less responsive to their surroundings. Some fish will also stop swimming and rest on the bottom of the ocean or riverbed. The amount of sleep that a fish needs can vary depending on the species and its individual needs, but many fish will sleep for short periods throughout the day and night.
It’s also worth noting that some species of fish, such as the swordfish, Marlin, Tuna, Mahi and other pelagic species do not appear to sleep at all, as they must constantly swim in order to pump water over their gills and obtain oxygen.
We all know that often times the morning is a hot bite. But then many times, afternoon is good as well. Mahi Mahi often seem to eat all day but the tuna fishing is good in the morning then again in the evening. Why is this? Then rarely can you ever catch a mahi mahi while fishing at night, but often times you can catch a tuna. But the tuna maybe you catch while chunking at night, whereas it is much less likely to grab a cedar plug or other trolling lure.
Swordfish of course eat better at night as do sharks but marlin is always better fishing during the day.
I believe alot of this all has to do with the fishes sleeping habits. And yes, they are not actually sleeping but they have reduced their activity and aggressiveness. Since most ocean fish tend to do this at night, sharks adapted to hunt during the night – much easier prey. Just like humans, the tuna wake up hungry from their rest, eat a bunch, take another rest then eat again later. Swordfish tend to just eat as they see fit and relax as they see fit, thus night and day bites possible. Marlin don’t have any predator so they just kind rest all evening and eat as they see fit throughout the day.
Would like to hear your comments on when fish eat in your area and when they sleep.