Difference in element accumulation and histopathology of Pontic shad (Alosa immaculata) migrants caught in the Danube River in interval of one decade

Abstract

Pontic shad (Alosa immaculata) is an anadromous species that lives in the Black Sea and Sea of Azov and migrates into the Danube, Don and other rivers to spawn. It is still economically important fish species in the Danube River. As the North-Western part of the Black Sea is heavily polluted investigation was performed to determine heavy metal and element accumulation in muscle tissue of Pontic shad as well as to record the level of histopathological changes. Pontic shad specimens were caught on 863 river kilometer of the Danube and the first investigation was performed during 2007 and repeated one decade later in the period 2017-2019. Element analysis was performed by inductively-coupled plasma – optic emission spectroscopy (ICPOES). In both sampling periods, only concentrations of arsenic (As), copper (Cu), iron (Fe), magnesium (Mg), strontium (Sr), and zinc (Zn) were above detection limit. Higher concentrations of As, Cu, and Zn were detected in 2007, while higher concentrations of Fe, Mg, and Sr were measured in 2019. Differences in concentrations of these elements, between sampling periods, were statistically significant. The gills of sampled fish were assessed using histopathology as a marker of general fish health state, using semi-quantitative scoring system. The histopathological results revealed different pattern of histopathological alterations in the gills of fish sampled during two distinct time periods. According to the method used, there were no difference in total gill histopathological index, but alterations were specific for fish sampled at two time points. Hyperemia and hyperplasia of respiratory epithelium dominated in fish sampled at the year 2007, while necrosis of branchial tissue prevailed in fish sampled a decade later.