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I'm a terrible insomniac, sometimes only getting a couple of hours kip in 24, and I have soft blue/white LEDs for night-time viewing of my tanks so I watch the activity at all kinds of hours. It never seems to stop. The only fish that seem to devote time to resting are the cats and tetras, and only for short periods. My african lake tank is full of life no matter what hour of day or night I have a look, which made me wonder if they actually sleep at all. Can anyone tell me?

if you have an African lake tank with -for example- Xenotilapia's or Callochromis; you'll see fish sleeping alright!
at night they can be handpicked from the tank with ease......during the day these streamlined fish are among the fastest cichlids from Lake Tanganyika

many fish are completely torpid at night and highly active during the day.
or reverse; some Auchenipterids are virtually motionless during the day and rest in the strangest positions in rootwork or dense plants. you can touch them in such a state.

some fish even make some sort of slimey 'bedding'; like the marine Parrotfish. this disables Reefsharks from hunting sleeping Parrotfish by smell; the mucuscocoon blocks the scent from leaking out and making the sleeping Parrotfish easy prey for Reefsharks or Moray Eels (nocturnal hunters)

some fish however never sleep.

my fish all just sit at te bottom of the tank

One thing that I notice in the small hours is that the colour of my fish seems to disappear as follows:-

1. Cardinal Tetras seem to fade to silver and lose their red and blue.
2. Discus go dark and lose all colour and go silvery
3. Bronze corys are very hard to distinguish from Albino ones
4. Sterbai corys lose most of their darkness and patterning
5. A 'Tiger' Pekoltia loses its light and dark brown stripes and becomes more of a uniform colour.
6. And two Bolivian Rams go white with a black spot.

This quickly sorts itself out when the sun comes up or the lights go on in the tank.

Tom

Yes, fish sleep.

As far as I know, all animals sleep. Even animals which are always on the move, like swifts (which can stay airborne for months) or pelagic fish like tuna, sleep, although they sleep only seconds at a time.

I do not, however, know whether fish dream - but frankly I would expect that they do.

I wonder if, when the fish bunch up at night, they go into 'Meerkat' mode. One watch's whilst the others kip. And then swap over.

My Tetra's don't seem to disturb much when the Cory's do their surface run tho'. And I've had the Cory's flip other fish out of the tank.

i noticed the colour changes in my tank

when i used to have Angelfish, the red part on top of the eye would fade completely, And my clown loaches would go a deeper orange, more like brown, and the stripes would turn grey