# Fry - Growth Inhibitors



## Christine (Nov 4, 2005)

I know that some fish fry, for example bettas, release some type of hormone that inhibits growth of other fry. Do all/many freshwater fish do this? I have a lot of guppy babies in a tank and I'm wondering if I should split them up for better growth.


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## mousey (Jan 18, 2005)

my guppies all seem to grow at about the same rate.
One batch of swordtails i had seemed to need separating to get them to grow. After i removed the biggest another grew really quickly. i removed him and another started to grow.
The platys seem to grow at about the same rate.
just my 2 cents!
mousey


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## Damon (Jan 18, 2005)

I'm not sure if it has ever been proven that any fish releases hormones to stunt the growth of others. I have always believe so. Splitting them up will give better growth for many reasons.
They won't have to fight as hard for food.
The water will stay cleaner
They have more room to grow and more room means less stress.


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## TheOldSalt (Jan 28, 2005)

Separating the fry will increase growth rates quite a bit, for the reasons Simpte gave and because of GIH ( growth inhibitor hormone ) buildup. 
GIH is used to control the size of the fish in a population within a body of water. If there are too many fish of too large a size in a body of water, the GIH will build up to the point where it stunts the growth. This is to prevent mass starvation. A given body of water can only support so many fish with food & such, but smaller fishes can be crowded more successfully. If there are enough fish in the water to allow the GIH to build up, then things are probably pretty bad in that water, and the fish start to stay small in an effort to reduce their needs. It's really a pretty elegant system in nature, but annoying in aquaria, and since GIH is made to affect fry the most, you have to keep it from building up enough to stunt them. Water changes have the same effect as separating the fry.


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## Christine (Nov 4, 2005)

Thanks for the info guys! One more question about GIH.. is it species specific? It seems from the above explanation that it would not be and that it would affect all fish in that body of water?


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## TheOldSalt (Jan 28, 2005)

It is largely species specific, or at least family specific. The thing is that all the species in the lake are exuding it, so it doesn't seem to much matter.
It wouldn't make sense for a predator to exude GIH meant to retard the growth of it's prey, would it? On the other hand, keeping down the size of competitors for the same foods would be a good thing. Like Simpte said, we're just starting to get a handle on this system, and so we don't have it all figured out yet. I do know that the GIH of some species has no effect on many other unrelated species. That in itself is pretty odd, for most hormones are widely effective on a broad array of species.


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