# what causes fish to grow bigger?



## mousey (Jan 18, 2005)

I always thought that the bigger the tank the bigger the fish up to the point that they grow to the size of their own species. And I find that the fish fry grow faster in the larger tank. However a friend who has had fish for many years told someone the other day that fish growth is caused by the depth of the water. Fish grow faster and larger if the tank is deeper.
he was talking about when he lived in Africa-- his tanks were taller than wide and they got a lot of big fish there. 
He also said that when the fish got too big, he took them back to the fish market and traded them in for smaller ones.


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## humdedum (Feb 18, 2009)

Unlike warmblooded animals, fish can keep growing for the rest of their life if fed well. 

Ordinary fish, so to speak, wlll indeed grow up into their species size. For example, many convicts are considered "normal" at up to 6 inches. But I know one convict who is nearly eighteen years old and nearing a foot long.


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## emc7 (Jul 23, 2005)

I know veil-tail angels will get bent fins in raised in short tank. I also know you can make fry grow faster by lots of big water changes and/or larger tanks. Something about the fish excreting and detecting something in the water that tells them to slow growth when they are in a small body of water (like a drought or dry season). So I always assumed it was the volume that matters. I saw a time-lapse video a while back of some discus grown in a 2 gallon tank with 1 gallon water changes every hour all day long. It proved you could grow fish quite fast in a small tank.

Some of the biggest of any species I've seen were from huge tanks and ponds.


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## girth vader (Apr 24, 2006)

a couple key factors that can hinder or promote growth are food and stress. The better the food the faster the growth, but the stress factor plays a bigger role. When fish are stressed they produce a chemical (HPI), which was referred to earlier. This is why you never empty a bagged fish directly into the tank after aclimating. You always put them in an container and either net them out, or I use my hand to put them in the tank. You dont want those cheimicals in the tank. The others will pick up on that stress and it will stress the other inhabitants as well. Water conditions stress fish out, hindering growth, poor tank arrangement will also cause this. Mbuna for example are much beter suited in a 75g then a 90g. Both have the same footprint, but Mbuna dont like going up to high to get food, it spooks them... Unless of course your rockwork goes up to the top of the water table....
And of course age plays a role. But the fish will never get old if stressed out....


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## TheOldSalt (Jan 28, 2005)

HPI is better known as "Shrekstoff." 
Well, okay, in certain circles it's better known as that.

Shrekstoff is a German word translating as "Shriek stuff," and is as the name implies a hormone released as a chemical alarm of a sort.

However, that's not the one to blame for retarded growth. That one would be GIH, Growth Inhibitor Hormone. When the level of GIH in a body of water rises to a certain detectable level, the fish stop growing. The reason it would rise to this level is that the population of that fish has gotten too high for that water for some reason.

In an aquarium, GIH buids up fairly quickly, and thusly the fish don't grow so well. Lots of regular water changes, however, remove this stuff and allow the fish to keep growing and growing as if they were in a big lake.

A taller tank has more water volume, and the more water volume you have, the lower your GIH level, and as such the faster the fish growth. It's not a matter of height, but volume. ( although tall fish like angels really need a tall tank )


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## mousey (Jan 18, 2005)

so it is not water pressure then that causes the fish to grow bigger?
My friend said higher pressure and larger fish! Doesn't sound just right to me.
Oh And my angel does have a bent top fin. He is in a 20 gallon regular tank.


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## TheOldSalt (Jan 28, 2005)

Nope, it'd not the pressure, but dilution of GIH by a larger volume of water.


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## emc7 (Jul 23, 2005)

But if you have higher water pressure, it takes less time to do water changes, making them more likely to be bigger.

If you breed the angel, and raise the fry in a 55, the fry's fins will likely be straight.


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