I guess we have to admit the possibility that at least some fish might adjust their size to their environment with out causing health problems? Is this a reasonable conclusion? I would have to say that there has to be limits. I wouldn't expect a flathead catfish to stay at 3" because I was keeping it in a 5 gallon tank. If I thought that was true I would be looking for a Wels Catfish! (I always wanted one!)Here is the opinion of a large fish seller called LA Fish:
A: My verdict, based upon the wisdom of Solomon, is that some do and some don't. We've all seen goldfish that kids win in contests and keep (or their mom's keep) in 2.5 Anchor-Hocking flat fishbowls. I get reports that these comets have survived in these quarters for 5 to 8 years. (Maybe it just seemed that many years?) At the local golf course and park ponds (in the absence of blue herons, channel cats, and raccoons), they'd grow to a foot or more and live beau coup years.
In the 600 gallon pond we used to have in the middle of the room (1,400 gallons per hour waterfall, 50% daily water change, and coin-operated food machines for the kids), we never had an iridescent shark grow over 18 inches. Of course they were competing with koi and tinfoil barbs.
Cindee McDonald reports a 13-year-old at 27 inches in 900 gallons
Lori Clarke reports a 15-year-old at 23 inches in 195 gallons
Lucas Jiang reports that they grow to 7 kilos in 50 x 50 ponds
If you put plastic plants at the ends of their tank, they won't ram the ends.
Anyway, most fish will stunt with minimal problems. You know those sunfishes just get dinkier and dinkier in most ponds and out compete the bass (in the absence of channel cats and rotenone). Those dinky sunfish are not handicapped in any way except size. They just adapt to their environment.
Several of my customers have said the chain pet stores tell them pacús will only grow to 6 inches. It could be to sell more pacús, but more likely it's because they don't know any better. Maybe both. LA
PS You'll still get various opinions, because people believe what they want to believe.
MatsP wrote:None of this explains the fish i had and the ones I have seen that are much smaller than they are supposed to be and yet they are healthy, alert, and don't show any of the signs you would expect to see in a fish that had been stunted.
And how do you know it was not already mistreated in some way before you got it (perhaps they were in a pond with it's relatives, and "choosen" for the aquarium trade because it was only 3" when it's "friends" were at 6").
I can't explain why your particular fish is smaller than the genetic ability of these fish, nor why it's being more mild-tempered than the average fish of this genus.
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Mats