Linear Growth of Sparsely Rakered Whitefish Coregonus lavaretus (Coregonidae) of the Imandra Lake (Murmansk Oblast) / Zubova E. M., Kashulin N. A., Terent’ev P. M. [et al.] // Journal of Ichthyology. – 2016. - Vol. 56, №. 4. - P. 588–599

596 ZUBOVA et al. mately 50% of fish in the period of active growth and 50% in the period of absent growth). According to our results, the observed length estimate corresponds bet­ ter to the calculated one at the time of the formation of an annual ring in the current year (Fig. 5b). Both the calculated and observed values of length in the whitefish grow up to the age of 5 years (p < 0.001) in the Babinskaya < Yokostrovskaya < Bolshaya Imandra series (Table 5). The distinction in fish lengths is determined by the absolute increase in the first year of life, which is the greatest in the Bolshaya Imandra whitefish, smaller in the Yokostrovskaya Imandra whitefish, and the least in the Babinskaya Imandra whitefish. From the age of 3 years, the largest values of increases are already characteristic of the Babinskaya Imandra whitefish that grows slowly in the first year of life. The Bolshaya Imandra whitefish is observed to have the lowest increases from the third to the seventh year of life. The average annual increases in the Yokostrovskaya Imandra whitefish from the age of three years to the end of life occupy the intermedi­ ate position. The observed regularity of changes in the absolute increases in the whitefish leads to the conver­ gence of the growth curves at the age of 5 years, after which they diverge again. Comparing the specific growth rate in the whitefish from the different Imandra Lakes from the second year of life (this parameter cannot be estimated for the first year of life (Mina and Klevezal, 1976)), we see the same regularity of changes in its indices, just like in the absolute, increases from the age of 3 years (Table 5). The obtained results show that the higher anthro­ pogenic stress levels do no t lead to the reduced linear growth of fish in the first years of life, as was registered earlier (Moiseenko, 1997, 2002; Antropogennye modi­ fika tsii..., 2002). On the contrary, the whitefish grows in the polluted Yokostrovskaya and Bolshaya Imandra lakes comparatively faster than the whitefish from the conventionally background Babinskaya Imandra region. According to our data, the absolute linear growth rate in the whitefish in the first year of life is closely correlated with the quantitative indicators of zooplankton biomass: the larger is the zooplankton biomass, the higher is the linear growth (Fig. 6). Zoo ­ plankton is a main type of food for the sparsely rakered whitefish in the first 2 years of life (Reshetnikov, 1980). According to our data, the greatest zooplankton biomass is typical for the Bolshaya Imandra (Table 2), which determines the largest growth in length in the first year of life in the fish of this lake (Table 5). The least indicator of zooplankton biomass in the Babin- skya Imandra corresponds to the lowest linear growth in the first year of life in the whitefish of this lake. The intermediate values of growth rate at the same age in the Yokostrovskaya Imandra whitefish can be explained in the same way. From the second year of life, the absolute linear increases abruptly fall in the Й ГО bJ 400 300 200 100 0 (c) 0 1 2 3 4 5 6 Age, years Fig. 5. Observed and calculated length (FL) in the sparsely rakered whitefish Coregonus lavaretus in the Imandra Lakes: (a) Babinskaya Imandra, (b) Yokostrovskaya Iman­ dra, (c) Bolshaya Imandra. whitefish of the studied lakes and already do no t depend on zooplankton abundance. At the age of 3 years, the sparsely rakered whitefish for the most part passes to the benthic feeding type (Reshetnikov, 1980). However, the highest benthos biomass in the Yokostrovskaya and Bolshaya Imandra in comparison with the one in the Babinskya Imandra (Table 2) does no t lead to greater linear increases in the whitefish of these lakes from the age of 3 years to the end of life (Table 5). Probably, the whitefish of the Yokostrovskaya and Bolshaya Imandra that grow fast in the first year of life are characterized by earlier development of sex products and, accordingly, by reduced increase in somatic mass. In this regard, we should have in view that the expenses for the develop­ ment of gonads can grow not directly before breeding, but earlier (Nikol’skii, 1974; Mina and Klevezal, 1976; Dgebuadze, 2001), in particular, according to our data (the values of the specific growth rate), from the age of JOURNAL OF ICHTHYOLOGY Vol. 56 No. 4 2016