Researchers determine the age of fish by counting growth rings on structures like scales, otoliths, vertebrae, and the operculum. The most common technique uses the sagittal otolith, as it records an annual cycle of opaque and translucent zones. Scales are also widely used due to their structure recording growth rates, while slices of vertebrae and the operculum examined under a microscope reveal rings that indicate age.

1. Age Determination of Fish
 Knowledge of fish age is necessary for stock assessment and
studying the population dynamics .
 So , researchers interested in determining fish age look for
structures which increase with age .
 The most widely used techniques involve counting natural
growth rings found on structures as ( scales , otoliths ,
vertebrae , operculum , etc…

2. 1- vertebrae & Operculum
 Cut the operculum or the centrum of vertebrae into number of
rings by jewellery saw .
 Slices are placed in glycerin in glass slide under microscope .

3. 2- otoliths
 Fish otoliths are earbones of teleost or bony fish.
 Function in hearing and equilibrium .
 Fish has 3 paires of otoliths : 1- Lapilli 2-sagitta 3- astersci
 The sagittal otolith is that used for age determination of most
fish ..

4. 3- Scales
 Are the most widely used for the determination of bony fish
age , which are provided with cycloid and ctenoid scales
 The structure of scales and its development is useful in
determining growth rate .