light on and light off

[megnmick]

This question is actually for a friend of mine. He just got a 55 gal. that has two seperate hoods on it. When he gets fish he says he's just going to leave one hood light on and the other off ALL the time. So one side is always light and one side is always dark. Is this a good idea? I don't think it is. Any opinions?

[madasafish]

Some would say it makes no difference....

I'd say that this will mess with the fishes' circadian rythms. They need some time in almost pitch dark (with a little "moonlight") to feel safe. Fish often change colors drasticallty in the dark--neon tetras are perhaps the best example of this. If the light's on in half the tank, the fish probably think they're under a mangrove overhang in one half of the tank, and in full river in the other.

Also, you'll notice if you turn the light off and put on a weak overhead lamp that the fish calm down and swim quite slowly in the dark (nocturnal fish exempted). My tetras and danios almost stop moving. The danios just rest at the water's surface.

So, I'd say that your friend's idea is ingenoius, but not natural.

[LondonGman]

I think all lights should go off unless he can mimic moonlight. Fish do things at night and they probably need a break from us

[Electrobes]

yeah the lights are most likely fluorecent too... its pretty good about lighting up everything anyway.. besides it would be like a person sleeping in a room with a lightbulb all the way to the otherside of the room... oh and lets also add that the person has no eyelids to shut his/her eyes... you get my point