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Goldfish Growth In New Tank


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I recently had to get rid of my common goldfish because he was being too aggressive with the fancies. So we gave him to a friend of ours who has a really big tank (I think it's like 200 gallons if I remember correctly but I'll have to check again later). The tank he was in at my house was only 50 gallons (which I thought was a huge upgrade when I bought it, lol...).

But I have heard that even in the short time that he's been there, he has grown a lot bigger than he was in my tank. I have heard so many things about the growth of goldfish, some say they grow as big as their tank allows and some say that's a myth. I thought 50 gallons was big enough for him to grow really big, but is it possible that he wasn't growing as much or as fast as he would have in a bigger tank? I just think the whole growth and tank size thing is very confusing.

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Well, there are two schools of thought on your question.

Some people think that goldfish secrete a chemical into their water that works as a negative feedback loop.

When there is a lot of the chemical in the water, it signals the fish that it should slow or stop growth because there isn't enough room-- hence why a feeder fish in a 1 gallon bowl will stay under 2 inches. More fish in the water mean that there is more of the chemical, so all the fish's growth will slow.

Since your fish is now in a much bigger volume of water, the chemical is so dilute that it is not inhibiting growth.

The other camp believes that instead of a special chemical/hormone, fish growth is regulated by the amount of nitrate in the water. Hence the more water/more water changes one does, the faster and bigger the fish will grow.

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Wouldn't regular water changes keep the growth hormone or the nitrates to low levels? I mean it makes sense what you are saying, it just seems kind of disappointing because even if you have a good sized tank and do regular water changes, your fish's growth might still be inhibited.

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There are a lot of points missing here that are needed to determine the differences aside from the size of tank. Are you're filtration systems pumping out at similar rates (oxygen)? Are there live plants (aids in nitrates)? Are feeding rituals similar? How many other fish are sharing the tank? What was the temperature of your tank (cooler temps promote breeding but not linked to growth)? I'm sure there a many other variables that I am missing, but it's an interesting mystery to solve.

Remember the basics: In order for a goldfish to reach it's maximum size (single tails 12-14 inches, double tails 10-12") they must be provide 10-15 gallons of space EACH. If any daily needs of your goldfish are not the best they possibly can be the fish will either halt or stunt it's growth until those conditions are provided.

Una

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  • Regular Member
Wouldn't regular water changes keep the growth hormone or the nitrates to low levels? I mean it makes sense what you are saying, it just seems kind of disappointing because even if you have a good sized tank and do regular water changes, your fish's growth might still be inhibited.

You would think so, but like Heidi and Una said there are SO many variables. There are all sorts of cues that influence growth, like genetics, feeding, age, lighting, and tank size. Common goldfish are meant to be in ponds and have a TON of space to swim-- perhaps having more area to swim stimulated growth? Or perhaps it was merely a coincidence and he was due for a growth spurt anyway.

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I know a fair amount of fish biology/physiology and have never been able to figure this one out exactly, but I am a firm believer it in happening! I know that every time I've upgraded tanks I've had dramatic increases in growth of my goldies. I've also seen it with freshwater fish like tetras. The most dramatic example I've personally seen though was my brother in law's shark. It was in a 15 gallon tank for years and slowly grew to nearly the length of the tank, but this took a long time. He gave it to a friend with a 200 gallon tank and it grew to the size of a large salmon within a few months, while essentialy eating the same amount of food.

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