What are Otolith rings?

Dec. 12, 2023

Recently, marine biologists at the University of Southampton have developed a technique to decode the chemistry of otoliths.

About Otolith rings:

  • The otolith is a stony lump in the fish ear.
  • These are much like tree rings which reveal fish's age.
  • Different forms or isotopes of oxygen in the otolith indicate the temperature the fish experienced when it was alive. Carbon isotopes reveal how quickly food was converted into energy.
  • Fish carry their fitness trackers in their ears. They are commonly known as "earstones," are hard, calcium carbonate structures located directly behind the brain of bony fishes. 
  • There are three types of otoliths, all of which aid fish in balance and hearing:
    • Sagitta: The largest of the 3 pairs of otoliths, sagitta is involved in the detection of sound and the process of hearing, or converting sound waves into electrical signals.
    • Asteriscus: This type of otolith is involved in the detection of sound and the process of hearing.
    • Lapillus: This type of otolith is involved in the detection of gravitational force and sound.
  • Different species have otoliths of different shapes and sizes; and cartilaginous fishes, such as sharks, skates, and rays, have none. 
  • Significance:
    • Features of otoliths can be used to identify the species, size, age, growth rate, and season of death of an individual fish.
    • Analysis of the oxygen isotope values of fish otoliths can provide information on the temperature of the water in which the fish lived.
    • While studying concentrations of trace elements such as barium can indicate the salinity levels of the water.

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