Relationship between different toxic effects of nickel on tolerance and recovery in the freshwater shrimp <i>Neocaridina davidi</i>

Nickel (Ni) is one of the metals present in marine and freshwater environments. By penetrating the animal body, Ni can accumulate in different organs, so many mechanisms may or may not be activated to eliminate degenerative changes at the cellular level. This study aimed to analyse whether exposure of adult freshwater shrimp Neocaridina davidi (Crustacea, Malacostraca) individuals to Ni leads to increased cell proliferation and whether any changes in the cell cycle occur. As the material for the study, we selected two regions of endodermal midgut: the intestine and the hepatopancreas, as organs having contact with different xenobiotics and taking part in homoeostasis maintenance. Additionally, emphasis was put on mitochondria, the organelles involved in cell death or cell survival, and the antioxidative system. We considered the changes that may occur in cells as a result of the animals returning to clean water after previous exposure to the metal. Thus, shrimps were exposed to an aqueous solution of Ni (3.63 mg Ni/l) for one and 2 weeks; then, to verify the reversibility of the changes occurring after exposure, the animals were returned to clean water for one and 2 weeks. Using qualitative and quantitative analyses, the experiment’s impact on the following parameters was checked: cell cycle, cell proliferation, mitochondrial potential, ATP, ADP/ATP concentration, Hsp70, mtHsp70, and MnSOD proteins. Our research showed numerous degenerative changes caused by Ni. Additionally, the return of animals uncontaminated water is insufficient for cell regeneration, despite the fact that some regenerative changes occurred.