Well a fish does grow to its environment and the more room you give it the bigger it grows. Ive never seen a fish where its organs burst out because it was kept somewhere small.
You can get goldies that are only a couple of inches long kept for a number of years in say a bowl with maybe a few litres of water and the fish grows very slowly, and the tell tale sign is a bigger head and maybe a deformed spine and or fins..
Here is a pic of my own fish that i bought from a fish store. She was kept in a display tank for two years and was only around 3 inches long. You can see by the head its too big and the fins are too short for a shubunkin.
http://smg.photobucket.com/albums/v...ent=P1010314.jpg&refPage=40&imgAnch=imgAnch48
She has been in my pond since july and ive just brought her in. I wish i had a pic but my camera isnt working but she is two inches longer and filled with eggs and doing really well.
Its not good for the fish as they are stressed and the lifespan is shortened.
I dont know if its been scientifically proven but I just dont believe that organs keep growing. You dont see it on people with dwarfism, any animal thats smaller than what it should be. Its just a myth to frighten people into getting larger tanks.
By the way im not saying to put fish in bowls either as its cruel and unnecessary, but for people to say the fish bursts open just isnt true. Im on a number of boards that deal solely with goldfish and its never been reported.
So if anyone can prove me wrong then I would love to hear it.
Fish that have opened up are those that live in ponds where they have picked up an internal parasite that wasnt meant to grow in them and the worm gets too big and comes out the side of the body.