“I don’t think they’re telling the truth.” This is probably what you’re saying in your head when you read that goldfish can live WELL over 20 years, while the goldfish you remember keeping last only lived 20 days. Will goldfish really live that long? I mean seriously? Although sometimes the life span of some fish such as goldfish may seem completely ridiculous, that statement may be at least partially true.
Many reasons why fish may die so early is simply because the water that it was living in was dirty. One reason why fish keepers are so “anti-fish bowl” is because most fish bowls are quite small (1 gallon or less). Fish bowls are okay for goldfish, just you must set it up right so it won’t get too dirty and such. Small tanks with large fish, especially fish like goldfish, means (possibly) dirtier water. Dirtier water could mean messed up water parameters (certain things in the water such as ammonia), messed up water parameters means (possibly) higher chance of your fish getting sick and dying.
For more convincing “proof” as you may call it, I myself have fish that have lived well over the 1 year mark (I know, crazy). This is actually not really long for most experienced fish keepers out there. There are many fish that can live much longer. In fact, the betta (which I also have) can live as long as 5 years! And the neon tetra, 1-2 years. So can fish really live as some say? Perhaps they can!
I never had a goldfish that lived 15 or 20 years and some say they can, but I do think they can. There’s even examples of goldfish that live for over 40 YEARS! The best way to keep your fish healthy and making sure they live longer could be as simply adding a filter and heater if it they need it. Most types of goldfish do best in cool water, so a heater is not recommended at all for them, but a good filter is always recommended.