Negligible senescence [neg-li-juh-buhl /si-nes-sens] refers to the lack of symptoms of aging in a few select animals. More specifically, negligibly senescent animals do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly senescent animals do not increase with age as they do in senescent organisms. Some fish, such as some varieties of sturgeon and rockfish, and some tortoises and turtles are thought to be negligibly senescent. The age of a captured fish specimen can be measured by examining growth patterns similar to tree rings on the otoliths (parts of motion-sensing organs). Study of negligibly senescent animals may provide clues that lead to better understanding of the aging process and influence theories of aging. The phenomenon of negligible senescence in some animals is a traditional argument for attempting to achieve similar negligible senescence in humans by technological means.
Some examples of maximum observed life span of animals thought to be negligibly senescent are: rougheye rockfish (205 years), Aldabra giant tortoise (255 years), lobsters are believed to live 100 or more years, hydras are observed to be biologically immortal, sea anemones generally live up to 60–80 years, freshwater pearl mussel (210–250 years), and ocean Quahog clam (405 years).