I’ve read more than once that goldfish will grow as big as their tank lets them…but do they become “full-grown” after a certain age like people do and a small tank stunts their growth, or would they get bigger in a bigger tank at any point during their life? (I’m thinking specifically of comets.)
I think the problem with tank size is the bigger the fish the more waste. The more waste in the water the more unhealthy the fish becomes. Unhealthy fish = stunted growth.
Most of the comet type goldfish I’ve had lived many-many years and got to be 5-6 inches in size. Some even bigger. This is in pond and large tank enviroments.
Their main growth slows in about 3-4 years. They continue gaining some bulk for several years after. Their lifespan is about 15-20 years in prime enviroments. I think the oldest recorded was around 40 years old.
Kind of seems sad when people put the little guys in bowls and they die 3 weeks later. Oddly, for such a dirty fish, unfiltered 1 gallon fish bowls are the WORSE place to keep them.