12. Ecological studies on the circulation of nickel in Abramis brama and Pomphorhynchus tereticollis from the freshwater ecosystem of the Danube river, Bulgaria

During the ecological study of 45 specimens of freshwater bream (Abramis brama (Linnaeus, 1758)) by applying standard techniques for parasites, an infestation with the acantocephalan Pomphorhynchus tereticollis was found. The aim of the present study is to establish the content of nickelin the water, sediments, parasites, tissues and organs of A. brama and its parasite Pomphorhynchus tereticollis, and the possibilities of accumulation and circulation in the freshwater ecosystem of the Danube River. From the tissues and organs of the studied specimens Abramis brama, the content of nickel in the skin samples was higher than in the liver and muscles and ranged as follows: Ni_skin>Ni_liver>Ni_muscles (in both infected and uninfected specimens).
The obtained values for nickel content in the liver and skin of the uninfected A. brama were found to be higher than the obtained values for nickel content in the liver and skin of A. brama infected with P. tereticollis. In contrast to that, the nickel content in the muscles of the infected A. Brama was higher than the nickel content in the muscles of the uninfected specimens of freshwater bream. The acanthocephalan Pomphorhynchus tereticollis showed significantly higher content of nickel than its host tissues and organs. Significant correlations (p<0.05) were fixed for relationships between С_{P. tereticollisNi} – С_liverNi, С_{P. tereticollisNi}– С_muscleNi и С_{P. tereticollisNi} – С_skinNi.

Keywords: nickel, Abramis brama, Pomphorhynchus tereticollis, River Danube