Fish are earlier than reptiles in the evolutionary tree, in most cases, (some were reptiles but returned to the water) so they probably don't as a general rule have spindling cells in their musculature, Spindling seems related to REM sleep paralysis, so I wonder do Fish have REM sleep?
Thank you Dr Fayza but I believe that Joachim has covered it with his web search.
Sleep in fishes is not extensively studied.[9] Some species that always live in shoals or that swim continuously (because of a need for ram ventilation of the gills, for example) are suspected never to sleep.[10] There is also doubt about certain blind species that live in caves.[11] Other fishes seem to sleep, however. For example, zebrafish,[12] tilapia,[13] tench,[14] brown bullhead,[15] and swell shark[16] become motionless and unresponsive at night (or by day, in the case of the swell shark); Spanish hogfish and blue-headed wrasse can even be lifted by hand all the way to the surface without evoking a response.[17] A 1961 observational study of approximately 200 species in European public aquaria reported many cases of apparent sleep.[18] On the other hand, sleep patterns are easily disrupted and may even disappear during periods of migration, spawning, and parental care.[19]
I'd be interested in the [18] 200 species European public aquaria study from 1961, if you could find the reference again. Thank you. Daud.
Some fish as I understand it, have a lizard evolutionary heritage from when they retreated back into the sea, during a die back. Can anyone tell me whether the zebrafish, tilapia, tench, brown bullhead, or swell shark have a reptile heritage? Thank you.
It could be that different fish have a different genetic heritage and only a small amount of them actually experience REM sleep but Joachim's search did bring up that a small percentage of 200 aquarium species according to Daud's quote tended to go through something closely resembling sleep, and that a smaller percentage had near mammalian sleep characteristics. If this is in error, I wish to know. Thank you.
Come to think of it, has anyone done one of those genetic comparison tests to see how far apart various fish species are? there might be a case of a wide range of genetic constellations over the history of fish species. If we knew which species corresponded to which historical retreat into the ocean we could possibly re-work the fishes genetic tree to keep it straight from a genetic point of view.
Just some observations of my own to add about fish sleep (sorry not about REM).
1. Parts of my fish tanks are placed in the basement, with artificial light that is turned on and off by a timer clock. One time I realized that many of the fish (especially cichlids) had a somewhat spiritless or slumber behavior over many days, maybe even some weeks. I did not realize, that the timer clock did not work and the fish had permanent light 24 hours over all that time.
2. But also in cichlids I made the experience that they do not really sleep deeply when it is completely dark. Because I remember when I got my first laser pointer many years ago, I was not only teasing my dog and cat with this brand new toy, but also the fish in the aquarium, and I could see, that the fish even tried to catch the red point, when the light was already off for hours.
3. Of course fish in aquariums are absolutely disorientated when after a while of complete darkness suddenly the light is turned on. Either they get in panic and run amok or they pretend like sleeping, and can then easily be caught. But imagine you could not close your eyes, and it would happen to you. But just use some red diodes (from a bicycle back light for instance) and watch an aquarium in complete darkness. You will be surprised how many fish are still active.
4. In this case I was very much surprised to see that little catfish of the species Tridensimils brevis are not only during daytime restless swimmers, but even more in the night, when they circle faster and their radius of movement is enlarged.
The Catfish of course have whiskers that they can use to detect other fish etc, as they move around. As such a night activity cycle is much more likely than a daytime one, they are not as reliant on their sight.
I believe that some mammals and birds have REM sleep , but cold-blooded animals such as turtles, lizards and fish do not.
How would you test to find out?
is there such a thing as a fish EEG? EOG? etc.
To answer this question we have to distinguish between behavioral quiescence and what we call sleep in mammals (and birds and a few higher reptile species). Fish certainly exhibit occasional quiescence, but the literature I reviewed several decades ago (published in , Biology Data Book, Fed. Amer. Soc. Exp. Biol., 1971) revealed no indication that they exhibit the slow EEG waves characteristic of mammalian sleep. In fact, their brain waves are continually activated. Nor did I find any indication of REM, which though it too has low-voltage, high frequency activated EEG, there was no report of rapid eye movements or muscular twitching that are characteristic of REM sleep in mammals.
http://thankyoubrain.com
The short answer is that there is no evidence of REM in fish. They definitely sleep, some probably sleep one hemisphere at a time (eg tuna).
I think it is porpoises that sleep one hemisphere at a time so they won't drown. Fish don't have to worry about drowning. I know of no evidence that fish "sleep." They do show behavioral quiescence -- see my earlier comment.
I discuss these and other ideas in my $9.95 neuroscience ebook, Core Ideas in Neuroscience. See http://thankyoubrain.com/neurobook/index.htm
In fact some species will drown if they stop swimming because they rely on ram ventilation
For key papers on fish sleep search for zebrafish and sleep in google scholar. They are used as models for understanding sleep in vertebrates . Eg:
http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0050277
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