I know of a pair of clowns which are more than 30 years old, and they are with a bubble tip anemone which has been in the same LFS for more than 40 years.
Few people realize fish generally live a long time - much longer than dogs or cats. When I set up aquariums for my customers - salt water or fresh - they would often have fish when their children were born, and keep those same fish when their kids went off to college.
I've had fish live more than 35 years (clown loaches). I traded an entire tank of New Guinea & Australian rainbowfish simply because I was bored with the seeing the same fish after 18 years. And I won't even get into how long some cichlids live.
Salt water fish are very long lived as well. Most should live at least 10 - 25 years.
Invertebrates are, for all intents and purposes, immortal.