Stunting fish for fun and for saving space.

There seems to be a lot of interest in "how big do fish get in captivity" lots of differences of opinion about why or why not fish get to be a large percentage of their maximum wild size. In my experience you can keep fish in great water quality and feed good nutritious foods, even live foods and still end up with a fish much smaller than it's maximum wild size.

As a point of evidence I have kept many iridescent sharks that stayed way below their "max size" most staying well below 12" and most in the 8 to 10 inch range. Even though the fish enjoyed summers in a large yard pond and winters in a 125 gallon aquarium with surface water return and trickle filtration the fish never grew past 12" or less. They lived for many years, as many as ten before something beyond my control killed them, they were all healthy active fish when they died.

It's my hypothesis that these fish become stunted when very small by being kept in a small aquarium where the pheromones they give off to adjust their growth rate keeps them from growing. later even if introduced to a larger habitat they still seem to keep their small size.

What are some possible mechanisms that would allow this size disparity to come about? Does this work on all fish or just some fishes? Are the fish raised this way on purpose as healthy and long lived as their wild counterparts? Is their anything wrong with adjusting the size of the fish to fit the aquarium rather than going for some arbitrary large size in captivity?

More basically, is it wrong to buy fish with the intent of stunting them so they can be kept in a smaller aquarium?

So, are we talking about "bonsai fish" here?

So, are we talking about "bonsai fish" here?

haha. thats a good question you propose. you could look at like well if you didnt keep a fish then the fish had a chance to be part of the food chain or other factors therefore you keeping said fish actually extended its life.

This idea of stunting a fish to make it easier to keep from the stand point of space often gets some highly negative comments, mostly I think, due to the old pet shop idea of fish only growing to the size of their container. While this is not true in most cases it is true that fish are often adaptable enough to allow themselves to adapt to the size of the pond or stream where they live in the wild. Food, space, competition, many things can affect the growth rate of fish but what I am talking about is a permanent stunting of the fish with out affecting the health of the fish in a negative manner.

The first fish I ever tried this with on purpose was the iridescent shark, I've managed to get the process down to almost a science with the iridescent shark. I place one or more 2" I. sharks into a ten gallon tank, a good bio filter, and good food, daphnia and black worms are my favs but a good pellet like Hikari micro pellets are good too. I leave them in the ten gallon tank for a year to 18 months, few water changes but I often use emergent plants to help remove nitrogen.

Once the stunting has taken place (at least in Iridescent sharks) they tend to stop growing altogether or grow so slow you do not notice. I often give my fish summer vacations in yard ponds and bring them back when the weather turns cold in November. this process has allowed me to keep iridescent sharks below 10" for as many as ten years.

Channel catfish also seem to be affected this way, goldfish, koi, in fact every fish I've tried so far will respond to this by stopping their growth and staying smaller. Anecdotal evidence from the wild would seem to indicate that nearly all fish can be stunted this way.

It needs to be asked, is this cruel? Or do the fish live just as healthy and happy as any other fish that is allowed to reach a huge size? Taking the iridescent sharks as an example, is it better to dwarf 7 of them at 6" and keep them in a roomy 125 or is it better to keep one huge fish that can barely turn around in the same 125?

This idea of stunting a fish to make it easier to keep from the stand point of space often gets some highly negative comments, mostly I think, due to the old pet shop idea of fish only growing to the size of their container. While this is not true in most cases it is true that fish are often adaptable enough to allow themselves to adapt to the size of the pond or stream where they live in the wild. Food, space, competition, many things can affect the growth rate of fish but what I am talking about is a permanent stunting of the fish with out affecting the health of the fish in a negative manner.

The first fish I ever tried this with on purpose was the iridescent shark, I've managed to get the process down to almost a science with the iridescent shark. I place one or more 2" I. sharks into a ten gallon tank, a good bio filter, and good food, daphnia and black worms are my favs but a good pellet like Hikari micro pellets are good too. I leave them in the ten gallon tank for a year to 18 months, few water changes but I often use emergent plants to help remove nitrogen.

Once the stunting has taken place (at least in Iridescent sharks) they tend to stop growing altogether or grow so slow you do not notice. I often give my fish summer vacations in yard ponds and bring them back when the weather turns cold in November. this process has allowed me to keep iridescent sharks below 10" for as many as ten years.

Channel catfish also seem to be affected this way, goldfish, koi, in fact every fish I've tried so far will respond to this by stopping their growth and staying smaller. Anecdotal evidence from the wild would seem to indicate that nearly all fish can be stunted this way.

It needs to be asked, is this cruel? Or do the fish live just as healthy and happy as any other fish that is allowed to reach a huge size? Taking the iridescent sharks as an example, is it better to dwarf 7 of them at 6" and keep them in a roomy 125 or is it better to keep one huge fish that can barely turn around in the same 125?

Well... I'm not going to say much about this except for it seriously annoys me to no end that many Internet fish warriors seem to spend much more time on talking out of their butts about record sized fish and "small tanks" than they do giving any sort of useful advice on husbandry of said fish. It is a really annoying trend that seems really popular. Many species can be easily kept in standard aquaria without much issue if you just take the time to actually do some homework. So called stunting, Often just Growth regulation or manipulation... does not in a number of cases prove harmful or Unethical. With an understanding of what you are actually doing it can prove to be a useful captive husbandry method.

I'm not completely sure what causes the fish to stop growing but i am sure pheromones during a critical time have something to do with it. I always feed my fish lits of live food and pellets but i do not strive to stuff my fish to over flowing with food, a typical tank set up to dwarf fish would have a thick layer of mulm over th fine sand, lots of plants, and a sponge filter. I often use a power filter to draw water into the sponge.

I am sure there are fish this will not apply to but so far so good! I think one of the problems with keeping fish small is that it goes against the grain of people who want giant sized fishes, they want five foot red tailed cats and all the attention keeping such a large brings. Bigger is alway better to these people but at some point you have to ask realistically "Will I really set up a new tank when that tiger muskie out grows my tank?"

In most cases the answer is no, so what do i do with the giant hammerhead lumpfish i just bought? In most cases the fish will die and the aquarist can blame the fish as being too big to keep and go on. What i am proposing allows us to see past the "maximum size" thing and see fish for the flexible adaptable animals they are.

I mean, which would you like to have, a school of 7 10" iridescent sharks in a 125 or one, 75lb meter long, iridescent shark, too fat to swim, unable to move forward more than a few inches as it just sits and waits for the next influx of food?

I think lots of people start out with good intentions but we all know what road is paved with good intentions

It needs to be asked, is this cruel? Or do the fish live just as healthy and happy as any other fish that is allowed to reach a huge size? Taking the iridescent sharks as an example, is it better to dwarf 7 of them at 6" and keep them in a roomy 125 or is it better to keep one huge fish that can barely turn around in the same 125?

Well Moon, you've opened a can of worms here. (Hmm, I wonder what that means. I mean, worms don't just spring out of the can and run all over the place, now do they?). With due respect to you and the Brookster, I would not do it. You are either keeping the fish on a starvation diet or you are otherwise making life barely tolerable for them. Your "either/or" scenario is one I would exchange for "neither". How about "stunting fish for fun and profit?" Would you look at it the same way? It isn't fun for the fish I would think. But then, neither is being kept in a glass cage.

Kinda makes me think of that famous story by Ted Sturgeon, "Microcosmic God". It's appropriate in more ways than one

Well Moon, you've opened a can of worms here. (Hmm, I wonder what that means. I mean, worms don't just spring out of the can and run all over the place, now do they?). With due respect to you and the Brookster, I would not do it. You are either keeping the fish on a starvation diet or you are otherwise making life barely tolerable for them. Your "either/or" scenario is one I would exchange for "neither". How about "stunting fish for fun and profit?" Would you look at it the same way? It isn't fun for the fish I would think. But then, neither is being kept in a glass cage.

Kinda makes me think of that famous story by Ted Sturgeon, "Microcosmic God". It's appropriate in more ways than one

Reduction in a fishes growth does not always have to be from starving them or making them live in a toilet bowl... You can also directly manipulate them through environmental factors such as Temperature. It is an interesting thing about Ectothermic animals that you can delay growth then easily restart it by manipulation of environmental conditions. If you understand the species you are working with this can be a management technique. I am BTW not saying this is something that is non species specific. You very much need to know the hows and when as well as the ins and outs of the species your dealing with.

Just let 'em be fish, I says.

Just let 'em be fish, I says.

No fault in that...

My interest in the idea of fish stunting came about when a local petshop offered me an iridescent shark some one had "traded in" the fish was 10" long and according to him had been in captivity for several years. i had a pond in my greenhouse and thought the shark would be cool in it. To make along story short the greenhouse was blown down by a hurricane and I brough the fish inside to my 125. The next summer I put him in a Yard pond and he spent the summer in a 300 gallon pond almost alone but he didn't grow, subsequent summers in the pond didn't result in any growth and about 5 years after i go him a blue heron ended the fishes life prematurely.

But the small shark got my attention and i tried to see if I could replicate the dwarfing in another shark. It worked quite well, the first year or so of captivity seems to be the most important. Good food and good bio filtration is how I keep my fishes but the idea of fish only growing to fit their containers was "I thought" an urban legend started by pet shop owners who wanted to sell any fish the customer wants and when the deal breaker question "will it out grow my tank or how big does it grow" was asked it was in the pet shop owners best interest to answer "it only grows to the size of the tank"

I always felt this was a little bit too self serving kind of like the "native fish will not live in an aquarium" answer we all have gotten at one time or another when we asked the petshop guy if native fish could be kept in an aquarium.

Now I've found that most fish will not grow anywhere near as big as their supposed maximum size when kept in an aquarium. They often live long lives and look perfectly healthy except for the small size. I've never been one for doing lots of partial water changes, 25% year is a lot to me, I prefer to grow plants and keep the aquarium healthy by more natural ways.

The build up of phermones is the best explanation of the fish not growing fast but why do they not continue to grow when the fish is moved to a bigger tank with new water? I have seen some fish grow quite well when kept this way, three hog chokers grew from tiny big as your fingernail fish to 10" long along side the shark previously mentioned. so it's not necessarily a water quality thing and it does result in nice healthy fish, just smaller ones.

My interest in the idea of fish stunting came about when a local petshop offered me an iridescent shark some one had "traded in" the fish was 10" long and according to him had been in captivity for several years. i had a pond in my greenhouse and thought the shark would be cool in it. To make along story short the greenhouse was blown down by a hurricane and I brough the fish inside to my 125. The next summer I put him in a Yard pond and he spent the summer in a 300 gallon pond almost alone but he didn't grow, subsequent summers in the pond didn't result in any growth and about 5 years after i go him a blue heron ended the fishes life prematurely.

But the small shark got my attention and i tried to see if I could replicate the dwarfing in another shark. It worked quite well, the first year or so of captivity seems to be the most important. Good food and good bio filtration is how I keep my fishes but the idea of fish only growing to fit their containers was "I thought" an urban legend started by pet shop owners who wanted to sell any fish the customer wants and when the deal breaker question "will it out grow my tank or how big does it grow" was asked it was in the pet shop owners best interest to answer "it only grows to the size of the tank"

I always felt this was a little bit too self serving kind of like the "native fish will not live in an aquarium" answer we all have gotten at one time or another when we asked the petshop guy if native fish could be kept in an aquarium.

Now I've found that most fish will not grow anywhere near as big as their supposed maximum size when kept in an aquarium. They often live long lives and look perfectly healthy except for the small size. I've never been one for doing lots of partial water changes, 25% year is a lot to me, I prefer to grow plants and keep the aquarium healthy by more natural ways.

The build up of phermones is the best explanation of the fish not growing fast but why do they not continue to grow when the fish is moved to a bigger tank with new water? I have seen some fish grow quite well when kept this way, three hog chokers grew from tiny big as your fingernail fish to 10" long along side the shark previously mentioned. so it's not necessarily a water quality thing and it does result in nice healthy fish, just smaller ones.

"The build up of pheromones is the best explanation" I believe you are on the right track. Fish give off growth inhibitors when overcrowding occurs so food/oxygen requirements remain lower and carbon dioxide doesn't build up as quickly.
In rivers and streams since many fish spawn during flooding there is a risk of especially offspring getting caught in pools after the water recedes. If continued growth occured then those in the pool would soon starve or sufficate. Then when the water again rises the trapped fish can again enter the main water system they were intended to. Growth inhibitors are diluted and the fish can resume growth.
You can see the same kind of example in ponds overcrowded with stunted Bluegills.
I saw an example of this on a website (wish I could remember which one)that shown an experiment with trout I believe. They were confined to a small space as fingerlings but fresh water was constantly flowing through the container. They grew to the point they were crammed together so tight they could hardly move. You did say you hate to do water changes.
Also, if I remember correctly each species give off a distint growth inhibitor that affects only their type. I would imagine that the amount each species released would be determined by habitat and normal growth rate.
Your catfish most likely releases much more than the hog chokers since it can grow to four foot in the wild and comes from such a large river system. And btw they do spawn in during flood season.

This link I found is better than my speculation (and memory for that matter). Go to the bottom and read what AquariumPro has to say. http://www.aquariump...php/t-1457.html
Hopefully this has helped.