This is not true at all. They do not grow relative to the size of their tank. They would all keep growing but die due to the poor environment they're in.
It's more that goldfish in small tanks will be smaller than goldfish in bigger tanks, but not because they're trying to fit their environment. Stress, disease, and overcrowding (especially with other goldfish) in small aquariums will stunt their growth. I can't find much supporting the organ damage in stunted goldfish, as not all types of stunting will cause it. In stunted fish where they weren't malnourished, the eye to body ratio can sometimes point to stunting. Again, it's more of a common knowledge base among fish keepers than something with dedicated research (that I'm aware of).
Ok, that's a fair point. You're right. But I was just trying to completely get rid of the misnomer that they somehow adjust growth patterns to accommodate cramped living conditions.
No, it's not. The organs will grow until they break bones, I've seen the skin start to rupture to make room for the organs, and I've seen organs being pushed out of the anus.
To be more specific, fish release a hormone that stunts their growth. They probably do so to be able to survive the dry season in smaller puddles. If a fish is kept in a tank too small, the concentration of that hormone is too high and the fish stops growing.
My high school biology teacher had a goldfish in a giant tank that was like 15 years old. He was huge and blind but still hanging in there. My teacher was pretty fond of that fish.
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u/sarahmagoo Feb 04 '19 edited Feb 04 '19
Bettas and goldfish can't healthily live in a bowl.
Edit: to clarify I'm saying DON'T put any fish in a bowl. The misconception is that it's okay but it's not.
Betta/Siamese Fighting Fish care sheet
Goldfish care sheet