http://freshaquarium.about.com/cs/beginnerinfo/a/lifespan.htm?nl=1

Estimating the life expectancy of fish is a bit like arguing who is the best running back in NFL history, who was the best point guard in NBA or WNBA history, who is the best all time Ladies Professional Tennis player or who is the best all-time left-handed pitcher in MLB history. Several of the estimates in that article seem pretty consistent with what I've heard. Some were not.

The 3-5 year estimate for Bettas and guppies surprised me. Some others may surprise you. Sometimes I think aquarists (ok, me too) get tired of certain fish and neglect them while pouring more care into the tank(s) of newer acquisitions. That neglect may shorten the fish's lifespan. And we then think of them as shorter lived than they could be.

Not surprisingly larger fishes and predators have a longer life potential than smaller, forage fishes. Usually the smaller fishes, including wild guppies, will not survive for even a year.

As a comparison, the eastern cottontail rabbit of the United States can live up to six years. But because they are preyed upon by a wide range of predators including humans, it is a rare cottontail that lives to an age of 12 months.

Shirley leaves out koi. Those colored carp, if kept from herons and raccoons, can live for 75 years. Cases of centenarian koi are known. So when building and stocking a koi pond, let your children and grandchildren know what may be down the road. ;)

That list is also wrong in some cases. They list "killie-fish" as 1-2 years. For annuals like the dazzling Nothobranchius, that is certainly true. There seems to be an internal timer, which clicks on "age" and at a certain point they just go down hill in a couple of weeks! However a South American "annual" in the person of a female Austrolebias nigripinnis resided with us on the cool floor of a townhouse basement for four years. And she had been someone else's fish before that!

By the way, most fish are still best bred at young adulthood. That may be 6 months for many killies and livebearers.

There are over 700 species of killifish and hundreds of strains of those, so a generalization is going to be tricky (a bit like all cichlids... or all livebearers or all characins...) Aplocheilus lineatus (wild color forms of the golden wonder killie) have lived 4-5 years here, if they don't find and jump out of any tiny opening in the tank cover. There is one female of a North American species that I entered in a show in 1997. She is still cheerfully scarfing down food in her 15-gallon tank.

I'd be interested in anyone else's impressions. Have you had a particular fish live as long as the estimated life expectancies? (That may not be entirely fair on a site mostly catering to newer aquarists, but maybe we can snag the thoughts of more experienced aquarists passing through.) What is your response to any particular estimate?