I am just curious, can goldfish or any other species see at night, I mean in complete darkness, when I turn off the lights? I think plecos do.....
I don't know about fish seeing at night, but I do know there are fishes that are in hiding all day and come out only at night. A lot of catfish are this way. Maybe they can see Who knows. Or maybe they only rely on their "feelers" (the barbels they have).
I'm not sure they "see" at night but fish have acute senses of smell.
maybe that's what my crab does, because they never come out during the day, at one point I thought he had escaped from my tank ( because he can climb up to the top of the tank where my hearter is placed) so I moved my rock and saw the crab hiding under neath it, I think he only comes out at night.