While many fish have relatively short lifespans, certain inhabitants of our oceans and freshwater systems can persist for decades, and even centuries. Understanding which fish live the longest and the biological mechanisms behind their extended lives offers insights into the diversity of life on Earth.
The Longest-Living Fish Species
The Greenland shark (Somniosus microcephalus) holds the record as the longest-living vertebrate. They can live for at least 272 years, with some individuals estimated to reach ages of 392 years, and potentially over 500 years. They inhabit the frigid waters of the North Atlantic and Arctic Oceans, often dwelling at depths ranging from 0 to 1,500 meters, though they have been observed deeper. Their extremely slow growth rate, less than 1 centimeter per year, is a factor in their exceptional longevity, and they do not reach sexual maturity until around 150 years of age.
The Rougheye Rockfish (Sebastes aleutianus), found in the Pacific Ocean, can live for over 200 years. Its extended lifespan is associated with its deep-sea habitat, slow growth, and late maturity.
Other Notable Long-Lived Fish
Many other fish species exhibit impressive lifespans across diverse environments. Sturgeon species (family Acipenseridae), found in both freshwater and saltwater, are known for their remarkable longevity. Lake sturgeon, for instance, can live up to 150 years for females, while males typically reach around 55 years. Other sturgeon species generally live 50 to 60 years, with many exceeding 100 years.
The Orange Roughy (Hoplostethus atlanticus), a deep-sea fish, commonly lives over 140 years, with some specimens estimated to be over 230 or even 250 years old. These fish inhabit cold, deep waters and are slow to mature, often not breeding until 20 to 40 years of age. Coelacanths (Latimeria chalumnae and Latimeria menadoensis) were once thought to live only about 20 years, but recent research using advanced aging techniques suggests they can live up to 100 years. Koi (Cyprinus rubrofuscus) can live for 25 to 35 years on average, and with exceptional care, some Japanese Koi have been documented to live over 50 years, with the oldest recorded individual reaching 226 years.
Biological Factors Influencing Fish Lifespan
Several interconnected biological and environmental factors contribute to the exceptional longevity observed in certain fish species. One significant factor is the consistently cold temperatures of their habitats, particularly in deep-sea or Arctic environments. Cold water slows down metabolic rates, which in turn reduces the rate of cellular damage and the accumulation of harmful byproducts, thereby extending an organism’s lifespan.
Another contributing element is a slow growth rate and delayed maturity. Species that grow slowly and reproduce later in life tend to have longer lifespans. The stable conditions of deep-sea environments, characterized by consistent temperatures, low light, and often reduced predation pressure, also promote slow life histories, allowing organisms to mature over many years. These conditions minimize stress and environmental fluctuations, which can otherwise accelerate aging.
Genetic factors also play a part in determining fish longevity. Studies on long-lived species like rockfish have identified specific genes and genetic pathways linked to extended lifespans, including those involved in immunity, inflammation, and DNA repair mechanisms. These genetic adaptations can enhance cellular maintenance and repair, contributing to a more robust and longer-lasting organism. The size of the fish can also correlate with lifespan within certain ecological niches, as larger body size can sometimes be associated with reduced predation and a slower life history strategy.
Methods for Determining Fish Age
Scientists employ various methods to determine the age of fish, particularly for those with extended lifespans. The most common technique involves analyzing otoliths, often called “ear bones,” which are calcium carbonate structures found in the heads of bony fish. Similar to tree rings, otoliths lay down annual growth rings, or annuli, that can be counted under a microscope to estimate a fish’s age. These rings reflect seasonal changes in growth, with opaque zones representing periods of faster growth and translucent zones indicating slower growth.
While otoliths are widely used, other calcified structures like scales, fin rays, and vertebrae can also exhibit growth rings. Scales are often used due to ease of collection, but they can underestimate the age of older fish. Vertebrae are commonly used for aging sharks and rays, which lack otoliths.
For exceptionally long-lived species like the Greenland shark, traditional methods are insufficient because their tissues do not calcify in a way that allows for growth ring analysis. For these extreme cases, radiocarbon dating of the eye lens nucleus is employed. The center of the eye lens is composed of metabolically inactive tissue that forms before birth, preserving a chemical record of the environment at that time. By measuring the levels of carbon-14 isotopes, particularly the “bomb pulse” from mid-20th-century nuclear testing, scientists can estimate the age of these ancient fish. This technique has been crucial in confirming the astonishing lifespans of the oldest fish.