This is a very good question, one that scientists are still researching. There is a fish called the Killifish that lives less than one year. It lays its eggs in temporary waters that dry up each season. The Catalina Goby is another fish with a short lifespan. This fish only lives for a year or two. In comparison there are the Groupers. Some species of Groupers may live 20, 30, or 50 years. Some scientists believe that Groupers may live to be 80 to 100 years old.