From what I understand, if you put a fish in a smaller tank like you often see goldfish in (Which can get up to 8 inches) the fish will put out a hormone that will stop its body from growing but the internal organs don't stop growing, which is why you see some goldfish with really big eyes. It also cuts the life expectancy. But that is what I've been told on here though it does make sense, since I had a 6 inch goldfish.
8 Inches is actually the very LOW end of the spectrum, something I am actually surprised Lupin did not point out, lol. Other than my three tiny baby pearlscales, my SMALLEST goldfish is six inches long, And I am talking fancies, NOT comets, commons or shubs.
I think its best to do whats fair to the fish you own. I've seen numerous promises of upgrading the tank size when they get larger, or doing more water changes to compensate, but they rarely actually follow through. The easiest thing to do is to simply get fish that your tank can handle, not the other way around.
I have to say that I agree here. It seems to me that the people that feel the need to make these types of excuses are the ones that are not going to follow through. Smaller than recommended tanks are not a death sentence for every fish. I will admit that I have three baby goldfish in a 30 gallon tank. BUT, I do really big water changes every other day (I did 80 percent water changes in my 80 gallon for MONTHS also) and these little fish have absolutely doubled in size in the last month or so.
I still say that tank size more often than not causes stunting. There are still too many people out there that think that twice yearly or even once monthly water changes are okay. There are still too many people that put a goldfish in a 1 gallon bowl, or a common pleco in a ten gallon with an oscar as a friend. Is it the stores fault for misleading the buyer? Is it the buyer's fault for not doing thier own research? Yes, and Yes. Blame can be apportioned to both.
So, I guess technically, it is a combo of water changes and tank size. Still, I can't see my ten inch + fantail goldfish Mei living in a ten gallon tank, even if I changed the water 4 times a day.
Kristina