Determination of fish age by scales and annual rings.

Age can be determined both by scales and by bones, by gill covers and rays of fins. The principle is the same everywhere. Every year, during the period of active life, good nutrition and a comfortable temperature regime, a new layer of the scale plate grows. It protrudes slightly from the previous layer, and this creates the effect of annual rings, like on tree trunks. In an unfavorable period, for example, in winter, the growth stops. With the onset of spring, a new layer begins to form. So one ring is one year of life.