What are Otolith rings?

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.