Species composition and morphological status of juvenile fish in the Koltsovo-Mordovin floodplain of the Saratov reservoir in 2017-2018

During 2017-2018, the proportion of individuals with various morphological disorders among larvae and fry of mass fish species in the Koltsovo-Mordovin floodplain of the Saratov reservoir, which belongs to the specially protected territory of the national Park "Samara Luka", increased, which may be caused by the impact of man-made pollution. The total incidence of abnormal fish larvae and fry reached 18.2% in Chub in 2017, 15.6% in bream and 21.1% in Rudd in 2018, which is more than four times higher than the established norm for healthy natural populations. However, the overall occurrence of abnormal fish larvae and fry in the Koltsovo-Mordovinskaya floodplain of the Saratov reservoir has significantly decreased compared to the previous study period (1995-2014), which may be evidence of normalization of the quality of water masses of the studied reservoirs and watercourses. It was found that the dynamics of occurrence of morphological anomalies does not correlate with the species belonging to individuals, but is directly dependent on the stage of development of the examined larvae and fry. With the highest occurrence of abnormal individuals in the early larval stages of development, such specimens are rare among early fry (stage E) and not found among late fry (F and G), which is proof of the lethal nature of all detected anomalies. By analyzing the occurrence of morphological anomalies in young fish of different age groups, it is possible to adequately judge the ecological state of the reservoir under study and the nature and quality of replenishment of the populations of mass fish species of the Saratov reservoir in the current environmental conditions.