Influence of toxicants on reproductive system of fish – representatives of different families in water bodies of the Dagestan part of the Middle Caspian Sea

In recent decades, a special vulnerability of the Caspian Sea ecosystem has been observed, which is exposed to the influence of large-scale anthropogenic impact. At the same time, the Caspian Sea is a unique ecosystem known for its numerous aquatic inhabitants. The most pressing problem of the basin remains the preservation of biological resources and the restoration of commercial Caspian fish stocks. Due to the limited number of studies on the reproductive system of different fish species under the conditions of probable influence of toxicants contained in the reservoirs of the Dagestan part of the Middle Caspian Sea, it was important to evaluate these features in commercial fish species of the carp, catfish, perch and pike families of the analyzed region during the last 20 years.
Complex studies in ecological-morphohistological and physiological directions at different levels (macroand microscopic) have shown that any disturbances in the morphology of reproductive systems of individuals of the analyzed fish species of the Caspian Sea (families of Carp, Pike, Catfish and Perch) can bring deep and irreversible changes in their structure and functioning. In the process of adaptation of fish individuals to new habitat conditions, profound changes occur in gametogenesis and gonadogenesis, in the passage of sexual cycles, in the rhythm of reproduction and in the ecology of spawning. The study of different parts of the reproductive cycle in fish species with different ecology, from different systematic groups, combining cellular, organ, organismal and population levels of research, showed that all parts of the reproductive cycle are closely interrelated; changes in one of these parts, caused by different conditions, are inextricably linked to changes in adjacent parts of the cycle.
Analysis of possible ways of fish adaptation to the changed conditions of reproduction in the studied water bodies after their reconstruction showed that the most frequent way of evolutionary transformations in different parts of the reproductive process is a change in the rate of development of reproductive glands and products of their activity (oocytes and spermatozoa) and the organism as a whole, which is reflected in the rate of reproduction of populations in the reconstructed water bodies of the Dagestan part of the Middle Caspian Sea. 

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