How is the age of a Fish
|Two methods are used to
determine the age of a fish -- growth "rings"
on scales, and/or ringlike structures found on otoliths
(small bones of the inner ear). The rings correspond
to seasonal changes, similar to the rings of a tree,
and can be counted to calculate the fish's age.
Examined under a microscope, a fish scale reveals
a series of fine ridges, called "circuli,"
in a circular pattern. A series of widely separated,
light rings form in the summer, when faster growth
that the life span of groupers and sturgeons can
reach 40-50 years. This grouper, native to North
Carolina, can live 20+ years and can reach weights
of more than 50 pounds.
During the winter, slower growth is indicated by narrow
separations between the rings, resulting in a dark band.
Each pair of rings indicates one year.
Because scales and scale rings are sometimes influenced
by other factors, such as pollution and contact with harmful
materials, researchers often examine otoliths, whose ringlike
structures also indicate years of life. Like scales, otoliths
exhibit a series of circular rings or bands around a center
point. White bands are formed during the spring and summer
months, while darker bands are formed during the winter.
The fish's age can be approximated by counting the light
and dark bands as one year.
Although scientists can obtain an accurate estimate of
a fish's age by studying these markings, little information
exists on fish longevity. Research reveals that the life
span of a fish can range from a few weeks or months (small
reef fishes) to 40-50 years (groupers, sturgeons). In fact,
scientists believe that some species of groupers may live
to be 80-100 years old. Most species, however, probably
live no longer than 10-20 years, with larger species generally
having a longer life span than smaller species.
North Carolina Division
of Marine Fisheries