Like all things born, fish too, have an age. It is actually a good tool in following a specific year’s cohort of fish. There are two ways to determine the age of a fish, one being non-lethal (meaning the fish will most likely survive afterward), and the other must be done after a fish has died.
The non-lethal method involves removal of scales (using tweezers), which will be prepared in a lab for reading. The lethal method involves the removal of the otoliths (paired bony-like structures which are located near the brain).
To determine the age, one should count the series of thin rings on the scales or otoliths.