How Old Was the Oldest Fish & How Do We Know?

Fish lifespans vary dramatically, with many species living only a few years, while others defy expectations by enduring for centuries. The study of these long-lived aquatic creatures reveals fascinating adaptations and provides insights into the aging process itself.

The Oldest Known Fish

The Greenland shark (Somniosus microcephalus) holds the record as the longest-living vertebrate known, with an estimated maximum lifespan of over 500 years. This large shark, which can reach lengths of up to 6.4 meters (21 feet) and weigh over 1,000 kilograms (2,200 pounds), inhabits the frigid waters of the North Atlantic and Arctic Oceans. Its existence in these deep, cold environments, typically between -2 and 7 degrees Celsius, is a significant factor in its extreme longevity.

This species exhibits an exceptionally slow growth rate, approximately 0.5 to 1 centimeter (0.2 to 0.4 inches) per year. Greenland sharks do not reach sexual maturity until they are around 150 years old. This delayed maturation and slow growth are characteristics that contribute to their extended lifespan.

Unlocking Fish Age Secrets

Scientists employ various methods to determine the age of fish. One widely used technique involves examining otoliths, also known as ear stones. These calcium carbonate structures, found in the inner ear of bony fish, develop annual growth rings similar to tree rings. By counting these opaque and translucent bands, researchers can estimate a fish’s age.

For some species, growth rings can also be observed on other calcified structures such as scales, vertebrae, or fin spines. Scales, while easier to collect, may sometimes underestimate the age of older fish due to erosion or regeneration. Vertebrae are frequently used for sharks and skates, which lack otoliths.

For extremely long-lived species like the Greenland shark, traditional methods are insufficient because their tissues are too soft to form distinct growth bands. In such cases, radiocarbon dating of specific proteins in the shark’s eye lenses is used. These proteins form before birth and do not degrade, allowing scientists to estimate age by analyzing the carbon-14 isotopes within them. This innovative technique revealed the age of the Greenland shark.

Factors Behind Longevity

The extraordinary lifespans observed in some fish species are influenced by a combination of biological and environmental factors. Cold, deep habitats play a significant role, as low temperatures and high pressure can slow metabolic processes. This reduced metabolic rate minimizes cellular damage and wear over time, contributing to extended longevity.

Delayed sexual maturity also characterizes many long-lived fish. For instance, Greenland sharks do not reproduce until they are approximately 150 years old. This strategy allows them to invest energy in growth and maintenance for a longer period before the energetic demands of reproduction. Genetic predispositions also contribute, as some species possess genes that enhance DNA repair mechanisms and immune system functions, supporting prolonged life. These factors allow certain fish to thrive for centuries in their specific ecological niches.

Other Notable Long-Lived Species

While the Greenland shark holds the record, several other fish species demonstrate remarkable longevity. The Rougheye Rockfish (Sebastes aleutianus), found in the Pacific Ocean, can live for over 200 years. Its deep-water habitat and slow metabolism contribute to its extended lifespan.

The Orange Roughy (Hoplostethus atlanticus), a deep-sea fish, is known to live for over 200 years, with some specimens estimated to be around 250 years old. This species also inhabits cold, deep waters and exhibits slow growth and late sexual maturity, reaching reproductive maturity at 20 to 40 years of age. The Coelacanth, often called a “living fossil,” can live for up to 100 years. This ancient lobe-finned fish was once thought to be extinct, but its rediscovery revealed its capacity for a long life, supported by its slow growth and low metabolic rate in stable deep-sea environments. Koi, a popular ornamental carp, can also achieve impressive ages, with some individuals known to live for over 200 years.