Fish that change color, when it’s dark???

[Magnum Man]

So, I was up before the tank lights came on again this morning, I do this occasionally, and I noticed something this morning… both of my Cupid Cichlids change colors… when they sleep… when the lights 1st start coming on, they were both storm cloud grey, way darker, the stripe across their eye, and target not visible… none of my other various fish change color that much… I was worried there was something wrong with them, but 10 minutes after the main lights came on, they were colored up as normal… I have a pretty big variety of fish in the 4 tanks, that I often watch the fish wake up, and no one else has ever done that???

I’ve noticed the Rummy Noses, will often be not as bright of red on their heads, if they are not group spawning at 1st light, and the electric blue rams, not as bright ( but I think they seem to rely on the tank light for their “electric” color ), but it’s also funny the electric blue Acaras are just as blue in the early light… but none of the other fish change as dramatically as those Cupids…

 

[Colin_T]

Lots of fish change colour during the day and night. They have nocturnal colours and diurnal colours. Nocturnal colours often involve a darkening of the entire body, or grey or dark patches on the body. Diurnal colours are what we normally see on fish in aquariums.

 

[Essjay]

Dwarf pencilfish (Nannostomus marginatus) show this day/night difference quite markedly. In the daytime they have horizontal stripes, and night they have vertical stripes.
Neon tetras turn brown at night.

Having had both those species, I was a bit worried the first time I saw the night colours/patterns.