Sandimirov S.S. Catalogue of lakes in the Russian, Finnish and Norwegian Border Area. Finland, Jyvaskyla: Kopijyva Oy, 2008.

moderate contamination. Lead has the highest Cfvalue. The degree of contamination value (8.3) for this lake corresponds to moderate contamination. Lake Layer, cm LOI Cu Ni Zn Co Cd Pb As cd Aittojarvi 0-1 56.12 65 44 92 2.0 0.31 15 1.4 28-30 34.15 74 22 58 4.0 0.25 7 0.96 c, 0.9 2.0 1.6 0.5 1.2 2.1 1.5 8.3 3.1.3. Hydrobiological studies Ichthyofauna. Studies on the fish community of Lake Aittojarvi were conducted in 2005. The most common fish in the lake consist of four species belonging to four fami­ lies: whitefish ( C oregonu s lavaretus), pike ( Esox ludus), perch ( Perea fluviati- lis ) and grayling ( Thymallus thymallus). Burbot ( Lota lota), minnow ( Phoxinus phoxinus) and nine-spine stickleback (Pungitius pungitius) obviously also inhabit the lake. Overall, whitefish pre­ dominates in Lake Aittojarvi. Other fish species make up 20 % of the catches (Fig. 59). Sparsely rakered whitefish inhabits the lake (up to 30 gill rakers). Its mean length is 22.7 cm, and mean weight 144 g.The maximum length does not exceed 40.2 cm and weight 852 g. Fish with a weight of200 g and length of 20-25 cm are the most numerous (Fig. 60). The bulk of the whitefish population is represented by 3- to 4-year-old fish (61%). Fish older than 7 years are oc­ casionally caught (Fig. 61). The ratio between female and male fish is equal to 1. Early maturity is a specific characteristic of the whitefish in this lake; some individuals in the lake become mature at the age of l+.The weight and size of fish spawning for the first time do not exceed 53 g and 18.4 cm, respectively. Table 40. Theorganicmatter contents (LOI, %)and heavymetals ( цд/д, dry weight) in the surface (0-1 cm) andpre­ industrial (28-30cm) sediment layers. Cf and С drefer to the contamination factorand degree ofcontamination values, respectively. Fig. 59. Distribution offish spe­ cies in LakeAittojarvi Catalogue o fLakes in the Russian, Finnish and Norwegian BorderArea 113