Dynamics of fatty acid composition in the muscles of crucian carp and pike under the influence of elevated concentrations of cobalt ions

In today’s conditions of growing anthropogenic pressure on aquatic ecosystems, the problem of heavy metal accumulation, including cobalt ions, is becoming particularly relevant. Cobalt ions can enter aquatic environments as a result of mining activities, metallurgy, and the production of batteries, dyes, catalysts, and magnetic materials. It is collectively may lead to local exceedances of permissible concentration limits in freshwater ecosystems. Despite the fact that cobalt is a biogenic element in low concentrations, its excess has a toxic effect on hydrobionts, in particular affecting lipid homeostasis. One of the sensitive indicators of metabolic disorders in fish is a change in the fatty acid composition of tissues, which can be used as a bioindicator of toxic pressure and the functional state of the organism. The paper analyses changes in the fatty acid composition of the muscle tissue of crucian carp (Carassius gibelio Bloch) and pike (Esox lucius L.) under the influence of cobalt ions at concentrations of 0.1 mg/dm³ and 0.25 mg/dm³ over a period of 14 days. These concentrations correspond to 2 and 5 maximum permissible concentrations. Total lipids were extracted and transesterified to obtain fatty acid methyl esters, which were then analyzed by gas chromatography for the quantitative determination of individual fatty acids. In crucian carp, the influence of cobalt ions led to significant changes in the composition of essential fatty acids. In particular, the fractions of saturated myristic acid (14:0) and long-chain monounsaturated eicosenoic acid (20:1) increased proportionally to the concentration of the investigated metal, while the levels of stearic acid (18:0) and oleic acid (18:1) decreased. A more systematic effect was observed in pike muscles: the content of many saturated fatty acid fractions decreased compared to the control group, while changes in the proportions of key polyunsaturated fatty acids likely indicate impaired desaturase activity. In the pike organism, a more systemic effect of cobalt ions was observed, which consisted in a tendency to decrease the amount of most saturated fatty acids. Some nutritional indices for assessing fatty acids were also analyzed.