Is it true that a goldfish will grow only as much as its tank size allows?
—Paul Grazier, Fairborn, Ohio
The environment of a goldfish may limit its growth, all right, though not in a healthful way. If the tank is large enough to accommodate the fish at its full genetic growth potential (which varies with the type of goldfish), the animal will achieve that size and grow no larger, even if the tank is huge. But if the tank is not large enough for the type of goldfish to grow to its full natural size, the animal will likely be stunted, unhealthy or die before living out its normal life span.
This is often the reason goldfish don’t seem to live long.