Lipids are a heterogeneous group of chemical compounds that are found in all animal and plant organisms and combine based on common properties. The physiological role of lipids in fish is extremely important and diverse. They perform a number of functions, including energetical, structural, regulatory and others. The authors analyzed the data in the domestic and foreign literature on the structural and functional importance of lipids in fish. The role of lipids in the processes of adaptation of aquatic organisms to adverse factors of the aquatic environment (temperature, salinity, chemical pollution) by changing the ratio of certain classes of lipids, their fatty acid composition and spatial orientation of fatty acid "tails" in biological membranes. The regulatory role of lipids in the functioning of membrane enzymes is analyzed. The authors argue that to find the causes of reduced productivity of fish in a polluted aquatic environment, it is necessary to study bodily changes in lipid metabolism, which are one of the main structural and metabolic compounds, responsible for the formation of adaptive reactions. By adaptation to low temperatures the inclusion of polyene fatty acids in the membrane lipids increases and also increases desaturation. Caused by changes in the temperature of the adjustment in the composition of membrane lipids are aimed at maintaining the mobility of membranes. By adaptation to the temperature factor the level of saturated or unsaturated fatty acids, the ratio of the main classes of phospholipids and cholesterol, asymmetry in the distribution of proteins and lipids in the cell membrane may change. The effects of hydrostatic pressure and salinity of water on lipid metabolism in fish are analyzed. It has been established that phase transitions are largely determined by the same properties of membrane lipids as with temperature change. First of all, it is the degree of saturation of fatty acids, the length of their chain, the position of the double bond and the number of hydrocarbon atoms (pair or not pair). It is shown that in the organs and tissues or fish, involved in the processes of osmoregulation, during adaptation to salt water the lipid content increases. Under the influence of toxic factors in different species of fish a general adaptation strategy is traced, which consists of increasing the content of those lipid fractions, that maintain the energy status of fish for excretion and neutralization of toxicants, reducing the permeability of biological cell membranes to limit the entry of toxicants into fish organism.
The morphometric characteristics of the most common commercial fish were studied: carp – Cyprinus carpio L., pike – Esox lucius L., crucian carp– Carassius auratus gibelio Bloch. and perch – Perca fluviatilis L., two years old, with an average mass of 290–330 g., 300–350 g., 150–230 g. and 170–230 g. respectively, caught from the small rivers of the Western Podillia (Strypa, Seret, Zolota Lypa). It was found, that the indicators of full length, standard length, head length, head height at the back of the head, the largest and smallest body height in carp, crucian carp and perch decreased linearly in a number of rivers Strypa – Seret – Zolota Lypa. It is noted, that the values of the liver index in the investigated fish species differ significantly from the representatives of the rivers Seret and Zolota Lypa compared to the species from the Strip River. This indicator increases in the Strypa – Seret – Zolota Lypa range, except for the pike index, which is of the lowest importance in the representatives of the Seret River. All the fish species studied saw an increase in the gills index in a number of Strypa – Seret – Zolota Lypa rivers. The study demonstrated that the values of the Fulton and Clark fattening coefficients in carp, crucian carp and perch decreased in a number of Strypa – Seret – Zolota Lypa rivers. In pike the highest values of fattening coefficients were noted for fish from the river Seret. Considering the same age of the fish and relatively the same trophic conditions in the studied rivers, it can be assumed, that the differences in morphometric indices are due to different anthropogenic influence on the watercourses. In this case, the least favorable environmental conditions are in the Zolota Lypa river, which is obviously due to its complex pollution.
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