The annual ring is the annual growth of mineralized formations that are deposited on the scales, flat bones of the skull, otoliths (auditory bones), vertebrae and bone rays of fins. It is formed as a result of seasonal changes in the growth rate of fish and is used to determine the age of fish as well as to calculate the growth rate of fish.

If you examine fish scales with a microscope, you can see peculiar rings on them, very similar to those we see on a slice of a tree. Each ring is a witness to another year lived. With sufficient diet and warm water, the ring of scales is wide and light, with minimal activity and a deficit of food it is much narrower and much darker. According to the scales you can determine both the age of the fish and its length, by which it has grown in the previous year.

Exemplars up to 1 meter long have scales with a radius of up to 1 centimeter. The distance from the annual ring (initial) to the central part of the scale is about 6 mm. This information can be used to determine that the fish has grown by 60 cm over the course of a year. Gill covers can be used instead of scales. They have marks which are used to calculate the age. All favorable and unfavorable conditions of development are displayed on the bones and scales of fish in the form of layering. These formations are their peculiarity. A single plate that has grown over the year shows the conditions in which the individual lived for that entire period. It appears under the last year's scales.