How Can the Age of a Fish Be Determined by Its Scales?
Determining the age of fish is of importance to biologists for scientific reasons. A common method used is to examine a fish's scales. The cold-blooded metabolism of fish restricts their growth to certain times of the year, which is reflected in their scales' appearance. This method of determining age is safe for the fish, and the scales that are removed will regenerate after a short period of time.
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Purpose
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Wildlife biologists use fish scales to determine the age and growth patterns as a means of population management. This method is used because it can provide an accurate reading without harming the fish. The process is comparable to counting the rings on a tree, as certain telltale marks appear on the scales that indicate the fish's age.
Procedure
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After catching the fish, scientists remove three to five scales from its body and place them in a small envelope. Other information about the fish is written on the envelope, such as its size, species and where it was caught. Since readings can vary based on the individual fish, the scientists gather readings from several fish of the same species and then average the results together.
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Reading
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As a fish ages, its scales get larger. As fish do not grow during the winter months, a ring forms that indicates the passing of another year of its life. In essence, it is a matter of counting the rings on the outer edge of the scale to determine how old the fish is. In some cases, readings are performed by more than one scientist for accuracy.
Additional Information
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Scientists can also use the scale readings to determine the life history of a particular fish or fish breed. They can indicate the type of environmental conditions the fish has experienced, and growth patterns can be determined for time periods as short as two weeks.
Organizations
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The Northeast Fisheries Science Center (NEFSC) is one organization that began fish scale readings in the 1940s and continues to provide readings for wildlife organizations and government agencies such as the Environmental Protection Agency. They provide data from current readings as well as information that goes back several decades.
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