new fish!!

[Rikko]

No one's offended; just having a little fun..
Anyways, aquarists' observations over time about that sort of thing generally can't be reliable - there are simply too many variables in a home aquarium that aren't accounted for. I don't know of any lab experiments that have been conducted but I expect that the general laws of biology as I understand them should hold. In short: there is no mind over matter. The conscious mind cannot control biological growth just as it can't control, say, body temperature or blood pressure (directly - giving yourself a panic attack I'm not counting).
Quite often I got FW customers swearing up and down that their goldfish did great in a bowl and it only grew to 2" long (this is a comet that will reach at least 12" in proper conditions). They correlated the fish's size with the bowl - as though the fish determined that it was taking up x% of the environmental volume and thus was not permitted to grow anymore. They didn't consider that once the fish grew to 2" that their monthly regimen of doing a partial water change wasn't sufficient to purge wastes from the water - the fish was living in absolute filthy water and its growth was retarded by the wretched living conditions and not by being stubborn or clever.

That said, I have definitely noticed much higher growth rates from fish in larger tanks as compared to smaller ones. Is there something there? I still kind of doubt it, because then I go back to my discus-rearing days.. When they were in a 3 gallon tank I did a 50% water change every other day. They grew like stink. Once they were big enough I moved them to a 20 gallon and did maybe 25% every week to ten days. Growth rate slowed down dramatically.

Nay, I think water quality is the real culprit as far as growth goes. A large (read: will get large) fish in a smaller tank isn't guaranteed to be in sordid condition, but I'd bet money that the water is going to be noticeably poorer than the same fish in a larger tank.