The life span of a fish depends greatly on it’s size. Small species, with a high metabolic rate, use up the same number of heartbeats faster than larger animals with slower heartbeats. The general rule is the heart is designed to beat only a limited number of times.
Larger fish will tend to live longer lives than smaller ones. Smaller common freshwater livebearers live for two to three years, and gouramis three to four years. Larger catfish, calico sharks and some cichlids can live up to eight to ten years.