Believe it or not, all goldfish, from the five-for-a-dollar feeders to the prized fish show goldfish of Japan and China, are all the same species. The fantail is no exception. Your fantails' lifespans vary depending on the size of their home and how well you take care of them.
Fantail Life Cycle
Like all goldfish, your fantails lay eggs. These eggs hatch in two to three days depending on the temperature. They don't require food for the first 24 hours as the fry (that's fish-geek talk for "baby goldfish") will live off their remaining yolk-sack. At this point, fantail fry need small, live food to feed on. It takes up to a month for them to take ground-up fish flakes. At four months, they are basically tiny adults and can take normal goldfish flakes. It takes an entire year for fantails to reach sexual maturity.
Lifespan In Fish Tanks
The biggest threat facing your fantails is overcrowding. Unfortunately, most people keep goldfish in tanks (or even bowls) that are way too small. Goldfish need about five gallons per inch of water to be healthy. A small or poorly maintained tank can shorten the lifespan of your fantail and stunt its growth. Fantails in aquariums typically live about 10 years.
Lifespan in Ponds
While your fantail will face threats in ponds that indoor fish don't (when's the last time a raccoon ate your prized fantail out of an aquarium?), they generally live much longer than their indoor counterparts. Despite things like predators and weather conditions, fantails in a pond can be expected to live about twice as long as an aquarium-dwelling fish. This means a fantail in a pond can be expected to live about 20 years.
Adding Years to Your Fantail
These numbers are just averages and estimates. How long your fish lives depends a lot on you. You can do a lot to lengthen the lifespan of your goldfish. For example, strictly adhering to the five gallons per fish-inch rule will improve your fantail's health. If you avoid mixing your fantail with tropical species, clean the tank regularly, and feed your fish carefully, you can greatly extend the lifespan of your fishy friend.