The circles of deposition of the scales in the trout 27 Jan

The circles of deposition of the scales in the trout

To know how to protect a species and manage the human activities connected to it, it is important to know its biological characteristics, dynamics and behaviors.

The age, the growth rate of the trout and therefore the length reached at the first reproduction are decisive parameters. To estimate the age of the fish, we can analyze the scales deposition circles under a microscope. When the fish grows quickly between one circle and another of the scale, more space is formed, while in the periods in which the trout grows more slowly, each circle is closer to the next. As with tree trunks, the seasons can also be recognized from the spawning circles.

Also, the scales can tell us a lot about an individual’s life. The scale shown below

belonged to a female about 45 cm long, captured in the main course of the Biferno river. In it we can read that for several months (perhaps a year and a half) the trout remained swimming in the same spring waters in which her parents had deposited their eggs. In fact, at the center of the scale there are many circles close to each other, with a constant spacing, testifying to a cool temperature that is always the same over the seasons, typical of springs. This phase was followed by a migration downstream, towards places richer in food, as evidenced by a sudden widening of the distances between the circles. From this moment on, the succession of winters, summers and reproductive migrations can be reconstructed.


The release: