I can't say for sure, I have heard that some fish can live for many years. I can tell you that the 2 clowns I have in my tank I bought on August 9, 2003. I have no idea why I still have the receipt.
Scott
A Healthy Clownfish should live 20 - 25 years.
Banggai Cardinalfish 5 - 6 years.
A Zebrasoma Tang about 40 - 45, larger tangs should live 50 - 60 years.