Metal Toxicity: Effects on Energy Metabolism in Fish.

Metals are dispersed in natural environments, particularly in the aquatic environment, and accumulate, causing adverse effects on aquatic life. Moreover, chronic polymetallic water pollution is a common problem, and the biological effects of exposure to complex mixtures of metals are the most difficult to interpret. In this review, metal toxicity is examined with a focus on its impact on energy metabolism. Mechanisms regulating adenosine triphosphate (ATP) production and reactive oxygen species (ROS) emission are considered in their dual roles in the development of cytotoxicity and cytoprotection, and mitochondria may become target organelles of metal toxicity when the transmembrane potential is reduced below its phosphorylation level. One of the main consequences of metal toxicity is additional energy costs, and the metabolic load can lead to the disruption of oxidative metabolism and enhanced anaerobiosis.

Biological responses of whitefish (Coregonus lavaretus L.) to reduced toxic impact: Metal accumulation, haematological, immunological, and histopathological alterations.

Bioaccumulation of the main pollutants in the organs of whitefish, as well as their haematological parameters, were examined dynamically over a 40-year period in historically contaminated Lake Imandra. A quantitative histological analysis was performed to assess the physiological state of whitefish and histopathologies of organs, as well as their physiological and biochemical functions in the current period of toxic load decline. Biological reactions of whitefish from the historically contaminated area have been greatly modified in contrast to those of whitefish from the never contaminated area of the lake, and this shift persisted even after approximately 20 years of toxic load decline. First, high antioxidant status supports the body's systems, smoothing over the negative consequences of metal toxicity, phagocytosis and inflammatory reactions. Moreover, the defence mechanism of whitefish from the historically contaminated area actively uses the oxidative systems of nonspecific immunity. Second, the adaptive strategy is aimed at improving gas exchange without compensatory proliferation of gill structure, which increases their functional surface and reduces the distance to the bloodstream, as well as increasing haemoglobin in maturing erythrocytes. Third, the higher efficiency of endo- and phagocytosis was confirmed by detecting increased monocytes and macrophages in the peripheral blood and decreased melano-macrophage centres in the fish kidney. Elevated accumulation of Fe, Cu, and Se may serve a sign of liver pathology, while elevated accumulation of Zn and Co already indicates kidney pathology, which is confirmed by histopathological alterations.

Influence of Thermal Pollution on the Physiological Conditions and Bioaccumulation of Metals, Metalloids, and Trace Metals in Whitefish (Coregonus lavaretus L.).

The Kola nuclear power plant, which discharges warm water into one of the bays of subarctic Lake Imandra, significantly changes fish habitats. The temperature gradient of the lake is between 2 and 8 °C, which makes it significantly different from the natural temperature of the lake water. The stenothermal cold-water native species (lake whitefish (Coregonus lavaretus L.)), living for more than 40 years under conditions of thermal pollution, has adapted to this stressor. Moreover, this population differs favorably from the population in the natural-temperature environment in terms of its physiological state. Firstly, the hemoglobin concentrations in the fish blood are in the range of the ecological optimum, and secondly, it has a higher somatic growth, as estimated by Fulton's condition factor. One of its main adaptive mechanisms of ion regulation is an intense metabolism of Na due to the high respiratory activity of the whitefish in warmer water. An increased accumulation of Rb and excretion of Se, Mo, and Si are associated more or less with that feature. Under conditions of an increased water temperature, the main metabolic need is due to a deficiency of Se in fish. The intensive metabolism of selenoproteins may involve risks of toxic effects and the bioaccumulation of Hg, As, and Cu in cases of increased existing stressors or the appearance of new ones.

Fish response of metal bioaccumulation to reduced toxic load on long-term contaminated lake Imandra.

The present study analysed the response of whitefish (Coregonus lavaretus L.) to reduced toxicity after the long-term contamination of subarctic Lake Imandra. High concentrations of Ni, Al, and Sr in fish organs and tissues were accompanied by nephrocalcinosis, scoliosis, and myopathy during the period of intense contamination. After reduction of the toxic impact on the lake, the accumulation of Cu, Al, Sr, Cr, Pb, and Hg in the kidney, which is the target organ for toxicity, was two-fold less and that of Cd was 10-fold less in whitefish from the contaminated part of the lake compared with those in whitefish from the non-contaminated parts of the lake. The ecological success of whitefish from the contaminated part of the lake was associated with the limited accumulation of metals in organs and tissues and a more favourable physiological state compared with whitefish from non-contaminated parts of the lake. Redistribution models were constructed for essential and non-essential metals in the fish liver and kidney depending on the physiological state of fish. The results revealed changes in Fe and Zn metabolism: an increase in Fe and a decrease in Zn accumulation in the liver with increasing stage of liver disease and decreasing blood haemoglobin concentration. Furthermore, under the sub-toxic (except for Cu) conditions of Lake Imandra, the strategy of adaptive fish response is to preserve and maintain acid-base regulation system.