The relevance of this study stems from the impact of heavy metals on hydroecosystems due to increasing anthropogenic pressure. In particular, the intensive discharge of cobalt ions via industrial wastewater leads to concentrations exceeding safe levels in local water bodies. Although cobalt is an essential trace element, exposure to elevated doses has a toxic effect on biota, inducing destabilization of the lipid profile, the development of oxidative stress, and disruption of the antioxidant system. Heavy metals can accumulate in fish tissues and trigger systemic pathophysiological changes. Therefore, a comprehensive study of compensatory responses and biochemical markers in fish under conditions of cobalt intoxication is necessary to elucidate the fundamental mechanisms of metabolic adaptation in aquatic organisms.
The scientific novelty and theoretical significance of this study consist in the fact that, for the first time:
– patterns of changes in lipid composition, the intensity of lipid peroxidation, and the functioning of the antioxidant system in crucian carp and pike under the influence of cobalt ions have been established. It has been demonstrated that the higher ecological resistance of crucian carp correlates with fewer significant deviations in lipid composition and more stable functioning of the antioxidant system compared to pike;
– the “lipids–lipid peroxidation–antioxidant defense” system is characterized, allowing the mechanism of Co²⁺ toxicity to be described as a single process;
– it has been established that the primary targets of lipid peroxidation are polyunsaturated fatty acids: docosahexaenoic acid in crucian carp and eicosapentaenoic acid in pike, which leads to their depletion and a reduction in the nutritional value of fish products;
– It has been demonstrated that under stressful conditions, the pool of non-esterified fatty acids is replenished primarily through the destructive phospholipase hydrolysis of structural membrane phospholipids, rather than through the classical lipolysis of reserve triacylglycerols;
– the understanding of how the antioxidant and detoxification systems of fish function under conditions of chronic toxic stress has been expanded.
The practical significance consists in the fact that the above-mentioned parameters can serve as sensitive biomarkers of oxidative stress in fish and be used in aquatic environment biomonitoring systems. The results of the study should be applied in fisheries management to assess the physiological condition of fish and to model the effects of anthropogenic environmental changes on their metabolic processes and productivity. The identified changes in fatty acid composition can be taken into account when evaluating the nutritional and biological value of fish products under the influence of cobalt. The established mechanisms linking lipid peroxidation, changes in fatty acid composition, and antioxidant system activity may be useful in future experimental studies to assess the effects of other ecotoxicants and identify effective ways to mitigate oxidative stress.
The research results can also be incorporated into the curriculum when teaching courses such as “Biochemistry,” “Hydrobiology,” “Aquatic toxicology, “Experimental ecology,” and “Environmental monitoring” to students in natural science programs at institutions of higher education.
The first chapter of the dissertation presents a theoretical synthesis of scientific data on the biological role of cobalt and its effects on aquatic organisms. Based on an analysis of the scientific literature, the chapter describes the effects of heavy metals on lipid metabolism and the mechanisms underlying the development of oxidative stress.
The second chapter of the dissertation presents an overview of the experimental study and describes the biochemical and analytical methods used.
Chapters 3, 4, 5, and 6 present the results of the study and an analysis of the effects of elevated cobalt ion concentrations on the processes of cobalt accumulation in the gills, liver, and muscles of crucian carp and pike, changes in total lipid content, the fractional composition of nonpolar lipids, phospholipids, and fatty acids, as well as indicators of the antioxidant system and lipid peroxidation, which can be used to assess the condition of fish.
The study confirms the potential of using biochemical markers (fractions of cholesterol, phosphatidylcholine, sphingomyelin, phosphatidylethanolamine, polyunsaturated fatty acids, glutathione content, glutathione-S-transferase activity, and lipid peroxidation intensity) for assessing the toxicological status of aquatic ecosystems. It has been demonstrated that pike serves as a sensitive bioindicator of the early stages of cobalt pollution in water bodies, whereas crucian carp is a representative species for assessing the overall adaptive potential of the ichthyofauna under conditions of chronic stress.
