These tiny bones are located in the fish’s skull just below the brain and help with hearing and balance (just like the bones in our ears) and can reveal an amazing amount of information about the life of a fish.

Because they continually grow along with the rest of the fish’s body, the tiny bones have growth rings – just like a tree trunk – that can be counted to determine how many years a fish has been alive and how much it grew each year.[1]

Due to the nature of the crystals that help to form them, otoliths have a lattice structure that can also trap elements from the water the fish is living in. In this way, the bones act as a time capsule which scientists can examine to reveal where the fish grew up.[2]

Essentially, the ear bones let us learn the age and movements of fish over the course of their lives – crucial to effective monitoring and protection efforts.

This type of testing means the survival of Australian Bass, released into the Snowy River in an effort to revive the dwindling population, is not left to chance.

Over 200,000 hatchery-raised Bass were released between 2007 and 2009 as part of a restocking program. Scientists are now studying juveniles they have captured in different regions of the river to monitor the success of the program.

By comparing the chemical make-up of the otoliths of the fish they can find out how many are the hatchery-raised fish they released and how many started life in the river. This allows them to monitor survival rates, growth and the preferred habitat of the fish.

The information collected will help scientists to plan the best time and place to carry out future releases which should give them a big advantage in their efforts to revive Australian Bass numbers in the Snowy River.

[1] www.reef.crc.org.au/research/fishing_fisheries/fishage.htm

[2] www.marinebiodiversity.ca/otolith/english/home.htm