In this work, I try to approach some general concepts related to the study of stable isotopes. The processes through which isotopes go through. Stable isotopes of some elements are suitable for ecological studies. This is due to fractionation and discrimination processes that occur during their movement through ecosystems. These movements happen due to natural cycles, which the elements undergo in one of their forms. Thanks to these cycles, isotopes enter the bodies of organisms. I especifically focus on fish tissues, primarly on otoliths. To determine the usefulness of otoliths in ecological studies, it is necessary to know their appropriate use, and the appropriate use of other tissues. The aim of this work was to gather information about the possible link between stable isotope analysis and the study of otoliths. Their composition and the information that we can obtain by examining this composition, especially the isotope composition, can be helpeful in studying the course of the fish's life and the environment in which the fish has lived in
