Structural Features of Scales of Baikal Grayling Thymallus baicalensis under Conditions of an Altered Hydrological Regime

The number of circuli between annual scale rings of grayling Thymallus baicalensis Dybowski, 1874 sampled in the Yenisei River in the downstream section of the Krasnoyarsk Hydroelectric Power Station, which does not freeze in winter, have been investigated and compared with populations of grayling from large tributaries of the Yenisei River (Amyl, Kan, Nizhnyaya Tunguska, and Bolshaya Kheta). It has been shown that graylings inhabiting the Yenisei River have a significantly higher (1.5–2.0 times, p < 0.01) number of circuli in the second, third, and fourth annual rings of the scales than in the populations from the tributaries, which corresponds to a higher growth rate of the grayling population in the Yenisei River. An assumption is made about the transition of graylings inhabiting the Yenisei River channel in the lower reaches of the hydroelectric station to a sedentary lifestyle.