Toxic effects of nickel on tolerance and regeneration in the freshwater shrimp Neocaridina davidi

Heavy metals cause environmental pollution and produce toxic effects on organisms. Nickel (Ni) is a common metallic pollutant of aquatic ecosystems and potentially can produce multifarious changes in the body of aquatic organisms. The average nickel content in rivers is about 0.7 μg/l. As a result, the homeostasis of the affected organism is disturbed, and processes that can counteract the changes are activated. To better understand the effects of Ni in the freshwater environment and its fauna, it is important to establish whether all changes caused in cells and tissues by Ni exposure are reversible when the animal returns to the non-polluted environment. Thus, the main aim of the study was to analyze changes that occur after Ni exposure and after it is returned to non-contaminated water at various levels of the animal’s body. The freshwater shrimp Neocaridina davidi (Crustacea) was selected as the subject of the study. As the organ for studies, we chose the midgut because it is a barrier against stressors that enter the organism. A concentration of 3.63 mg Ni/l was selected for the experiment, at which approximately 50% mortality of the population was observed after 14 days. The midgut was analyzed using light and transmission electron microscopy (TEM), confocal microscopy, and flow cytometry for qualitative and quantitative results. When the organisms were transferred to clean water, a prolong exposure resulted in a decrease in the values of the analyzed parameters (e.g. ROS, cell death, etc.) proportional to the purification time. The recovery time was insufficient to return to control values in most analyzed groups. Nevertheless, the occurrence of regenerative changes suggests that freshwater shrimps are relatively tolerant to nickel, when the exposure time is short and the recovery time is long.