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About otoliths (ear stones in fish)

An overview of otoliths, growth rings and what we can learn from them.

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Otolith definition

Otoliths (ear stones) are small, white structures found in the head of all fish other than:

  • rays
  • sharks
  • lampreys

Otoliths provide a sense of balance to fish in much the same way that the inner ear provides balance in humans. Fish otoliths also aid in hearing.

Growth rings

To fisheries biologists, the otolith is an important tool for understanding the life of fish and fish populations.

Growth rings (annuli) record the age and growth of a fish from the date of hatch to the time of death. Daily growth rings form in the first year of life and record daily age and growth patterns in detail. However, they're only visible through a microscope.

Learning from otoliths

Virtually the entire lifetime of the fish is recorded in the otolith. Sophisticated chemical techniques can reveal:

  • hatching year
  • water temperature
  • migration pathways

For that reason, almost every fisheries laboratory in the world uses and studies otoliths. They also make ideal class or science projects, suitable for both high school and supervised elementary school students.

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