Circadian-rhythmic variations of biochemical parameters in the yearlings of indigenous perch (Perca fluviatilis L.) and nonindigenous tyulka (Clupeonella cultriventris Nordmann) from the Rybinsk Reservoir (Russia)

Abstract

Diurnal variations of some parameters of protein, lipid, and water metabolisms in the underyearlings of indigenous (perch, Perca fluviatilis L.) and nonindigenous (tyulka, Clupeonella cultriventris Nordmann) fish species have been analyzed. These species form the basis of feeding aggregations of young fish in the Rybinsk Reservoir pelagial. No significant daily fluctuations in the values of protein content, water, and lipids in the studied fish species were revealed. Stable interspecific differences in mean daily and hourly values of the above-mentioned components, as well as in the contents of three lipid fractions—phospholipids (PLs), free cholesterol (FC), and triacylglycerols (TAGs)—have been determined at the level of whole organism. It is shown that the level of adipose reserves and the content of TAG in the tyulka are higher than in perch, while the contents of proteins, PL, and FC are lower. Diurnal variations of the level of each of the three fractions in both fish species are similar, but the ranges of variations are wider in tyulka than in perch. Possible mechanisms for the regulation of lipid metabolism and their similarity in young fish of different species upon adaptation to short-term changes in the environment are discussed. It is suggested that the modern state of the zooplankton community in the Rybinsk Reservoir pelagial negatively affects the feeding of perch underyearlings and parameters of lipid metabolism in their organisms.