Age Determination of Fish

Fish age is estimated by counting seasonal rings in hard body parts such as scales, bones and otoliths. The basic principle is the same as counting rings on a tree. Fish growth is generally fastest in the summertime. Period of fast growth is represented in the scale or otolith as a wide light-coloured zone. Periods of slower growth, Finnish winterseason for example, are narrower and darker. Wide and narrow zones together form the annual growth ring.

Why do we need to know the age of fish?

For fish biologists (ichthyologists) the age of a fish is at least as important information as the length or weight of the fish. The age determination of the fish is used to find out the age structure of the studied fish stock, the strength of fish of different ages and how well the fish grow in general. Among other things, information on the state of fish stocks is needed for planning the management of fishing water and fish stocks

Try to determine the age of the fish at home!

You can try the age determination at home, using for example the scales of a pike or a bream. Use tweezers to remove the best possible scale under the lateral line of the fish or from the area between anus and the pelvic fins of the fish. Hold the scales against the light and try to count the number of annual rings using a magnifying glass!

How long do fish species in Finland live?

Fish keep growing throughout their lives. How long does a fish live? Depends on a fish specie. The sea stickleback (Spinachia spinachia) lives just a little over one year, while a sturgeon that once lived in Finnish waters can live for more than 100 years.The longest living fish specie of our current fish is an eel with a record age of 72 years. The oldest perch found in Finland was 29 years old and oldest salmon caught in Finland was 13 years old.

Brochure of Fish Age Determination (Currently in Finnish language only)