No they do not absoluley NEED to have the lights on but it is certainly of benefit to them for thier continued health. UV light is important for them to remain healthy in the long term & they will feel much more comfortable if there is a defined night & day.Aren't the number of hours lights are on for mainly for the health of plants? I always wondered whether fish need artificial light at all. Given the conditions most of them come from the bright artificial light we use are way more light that they would have experienced in the wild.
What can happen if they get 5 hours per day instead of 12 hours? Will they be ill?Yes fish do sleep but they have more instinctual body functions happening than humans when they do. Breathing, swim bladder control, pectoral fin control & survival instinct are all instinctual & require no thought on the fishes part. Us humans just need to close our eyes & breathe. The fish is asleep but it can do all of the body functions mentioned above & be aware of danger close by.
In thier natural environment tropical fish get about 9hrs of full darkness with a sunrise & sunset changing of the light period either side of that. A minimum of 8hrs lights out is needed IMO & 10hrs is even better.
They adapt to it, imagine all of the fish in places like alaska where in some parts during the summer it is daylight for 18 or even 24 hours a day.And what if fish have lights off but there is still light in the surroundings so that in reallity the fish get like 3hours to no time of "absolute darkness".
Oh you remind me that when I switch off the lights at 19:00, sometimes my father is still watching television and the aquarium gets a little light, but the fish are still active. Will they go to sleep when they want to at that time?And what if fish have lights out but there is still light in the surroundings so that in reallity the fish get like 3hours to no time of "absolute darkness".