# Do Fish Grow Faster If the Tank Is kept Dark??



## TheSimster (Jul 30, 2009)

One of the people at a LFS told me that if you keep the tank lights off a lot it causes the fish to sleep more and they grow faster. I was curios if this was true because i haven't seen it anywhere,is it?


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## BioG (Oct 12, 2008)

This has been speculated but I have not seen anything conclusive. Eating and movement are both essential to fish growth as well and it is better to provide a balance of light and dark. However, I did participate in a study in college where fish raised under dark green lighting did grow up to 30% larger in an alotted amount of time than those that were not.

Details of the study can still be found online I'm sure but I can fill you in if you like, although the "dark green" part is the jest  HTH


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## DeadFishFloating (Oct 9, 2007)

Not related to the lack of light theory.

One of our local hobbyists carried out an experiment with a small batch of fry he was growing out. He split the group between two 15 gallon tanks, with identical sponge filters and feeding regimes. The only difference was the water change schedule. One tank had a daily 80% water change, the other tank had five 20% water changes a day. After one month, the group which recieved five water changes a day were almost twice the size of the group that recieved one water change per day.


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## BioG (Oct 12, 2008)

True, water changes do seem to work

What do you mean by "Not related to the lack of light theory"


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## Toby_H (Apr 15, 2005)

BioG... what kind of fish did you use in your college experiment?

I know there are a lot of biological differences between cold water fish and tropical fish... and they are affected differently by a lot of things...

I've never heard the theory that fish in the dark grow faster... and I would heavily doubt it to be true...

It sounds to me like someone speculated "if they move less they burn less energy thus that energy can be used to grow."... which is simply not true. This might make them fatter, but not "bigger"...


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## DeadFishFloating (Oct 9, 2007)

BioG said:


> What do you mean by "Not related to the lack of light theory"


Just meant that my input to the discussion wasn't related to the "lack of light theory", but was on topic in regards to increasing growth rates.


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