nocturnal fish???

[Magnum Man]

so at 1st light, most of my fish are sleeping... I noticed when I had tin foil barbs, that they swam basic patterns unconsciously, so it didn't look like sleep.... but I have noticed my bitterling ( the tank is in an area of the house I rarely witness the lights 1st coming on ), are all out of their hidy holes, in the dark, and seem to disappear as the lights get brighter, consistently enough, that they seem to be nocturnal, aside from a few plecos, that also seem to only come out at night, and some predatory catfish I had previously, any other fish that are most active in the dark??? I assume they have eyes adapted to see better in the dark??? I didn't expect that out of the bitterling...

 

[GaryE]

I was really struck by how many of the fish I've seen in nature had strong light preferences. Mollies and bigger Central American Cichlids were out there in the sun, though the Cichlids liked having cover close in case they spotted birds. In central Africa, the Chromidotilapia also scooted around my legs in the open but seemed to keep cover in mind.

Other fish were never in the sun, in daytime. They hung around under overhanging bushes, or in leaf litter. I think we make a mistake when we put fish in brightly lit boxes where the light everywhere is the same. It's great for plants and for us looking at fish, but I doubt it's good for them. I now like having light zones in tanks - areas where the light strip is intentionally too short for the tank. I'll put a strong LED strip at 24 inches onto a 36 inch tank, and I see a lot of fish, especially smaller ones, avoiding the brightest areas except for food frenzies.

It's not directly about nocturnal fish, but there's something there. Stepping off a road into primary jungle puts you in the half light of late evening, even at noon around the equator. It's really striking how dark it can be in the habitats of many fish. It got to the point where when I walked up a stream, I would try fishcatching in the sunny stretches, but didn't expect much. As soon as there was an arch of vines or trees over the water, the net showed a lot more.

 

[Magnum Man]

the bitterling are in a highly shaded tank, so I wonder if they are truly nocturnal???

 

[GaryE]

From what I've read, it's a diurnal, daytime species. They may just shun bright light.