Why do the fish swim more when the light is off?

[Finzzup]

It's taken me a week to notice this.

My fish want to hover at the bottom of the heater when the aquarium light is on. It's a flourescent bulb... as soon as I turn off the light, they are swimming as happy as can be! Is the light hurting them? Do ALL fish do this?

These are Neons and White Clouds. The Betta seems to do whatever he wants whenever he wants...

[OrionGirl]

Nope, they aren't afraid of the light, and there is a simple explanation.

Minnows and neons are both heavily preyed on in the wild by flying hunters--kingfishers. When there's a bright light above, these fish are very noticable and an easy target for winged predators. They tend to hide, either in deep water, or in plants, and stay still so they aren't detected. I bet if you walk up to the tank and cast a shadow that crosses them, they dart suddenly about 1-2 inches, then freeze again, right? Adaptive behavior to avoid being a meal. In the wild, less light means either it's cloudy, so the predators don't have as clear a view into the water, or the sun is on an angle, which creates a lovely glint that prevents predators from seeing the fish below the surface as clearly.

Unless you need the lights for plant, I would opt to use only ambient light. Your fish will be more enjoyable to watch this way. If you do want some lighting, try changing spectrums to something lower--go for the overcast day instead.

HTH

[Anton Wernher]

Not sure about the white clouds however neons inhabit low visability waters for the most part. A tank with clear water and light is probably making them feel a little insecure. You might want to try staining the water a bit. It will probably make the neons more active and will really make them look better.

[Anton Wernher]

I like orions explaination better :)

[OrionGirl]

Don't give me too much credit--it was a special on the Discovery Channel that showed the neon predation...I just made the connection between that and the way my neons and minnows acted with my lights. I changed my light timer around so there's a significant time period where the room is well lit, but the tank lights are off. Makes it easy to watch those fish.

[RTR]

Or add plants - real or plastic - so that there is cover available nearby. When fish know/see cover nearby they will swim in the open more freely.

PS: My small fish are more active while the lights are on.

[Finzzup]

Originally posted by OrionGirl
I bet if you walk up to the tank and cast a shadow that crosses them, they dart suddenly about 1-2 inches, then freeze again, right?
Wow - I was looking around the room for cameras or something! Thought you had a view in here!

Yes, they do exactly that! Thanks for the fantastic explanation! I will work on changing the light somehow... I have kind of an overcast office -- I actually removed my overhead lights and left a small light in the front of the room, so I sympathize with the fish! :D

[Finzzup]

Originally posted by RTR
Or add plants - real or plastic -

RTR - I just did that yesterday and it DID make a difference! They didn't hang out under the heater quite as much, but they still do a LOT. When I turned off the light awhile ago, I was watching and I felt I was watching one of those old zombie movies -- the lights go out and the zombies start appearing in the room, coming out of all the hiding places...

[goldfries]

my fish can be more wild when lights are off too.

last i experimented having lights on/off, the moment i off the lights is when 1 of my tiger barb attacked my guppy. :p

hehe. well now guppies are never barbs in my place. they live peacefully until the lights were off. ;)

[kipp99]

Hi! :)

When I had my 10 gallon last year with 4 platies, I noticed that my fish too acted different when the lights were on and off. When the lights were on they chased each other and were more aggressive. When I turned the lights off the aggressiveness stopped.

Any ideas why?

Kipp