The fish fauna of Lake Frolikha comprises 12 species confirmed by our recent studies: roach Rutilus rutilus (L.), minnow Phoxinus phonixus (L.), stone loach Barbatula toni (Dyb.), spine loach Cobitis melanoleuca Nichols, pike Esox lucius L. lenok Brachymystax lenok (Pallas), Arctic charr Salvelinus alpinus (L.), Baikal black grayling Thymallus baicalensis (Dyb.), burbot Lota lota (L.), sand sculpin Leocottus kesslerii (Dyb.), stone sculpin Paracottus knerii (Dyb.) and perch Perca fluviatilis L. Biological peculiarities of these fishes are determined by unique geographical position and limnic characteristics of Lake Frolikha. Being a typical glacial lake it is located at rather low altitude a.s.l. and is adjacent to the unparalleled ecosystem of Lake Baikal. An underdeveloped shallow coastal zone with sparse aquatic vegetation, which is characteristic of glacial lakes, determines some biological traits of Lake Frolikha cyprinids. As compared with other mountain lakes of Baikal Rift Zone (BRZ), roach and minnow have lower rates of linear and weight growth as well as unusual population sex ratios. Male to female ratio in roach is 2:1 and in minnow it is 1:1 whereas in other lakes it reaches 1:4 and 1:10 respectively. The presence of native Baikal species in Lake Frolikha provided abundant food for piscivores: sand sculpins are the dominant food item of lenok, Arctic charr and perch. Lenok and perch demonstrate prominent linear and weight growth rate in the lake. In other lakes of BRZ with less abundant prey fish species Arctic charr typically diverge into several trophic forms, but in Lake Frolikha they established a monomorphic mostly piscivorous population. Charr from Lake Frolikha are relatively small and short-lived representatives of the large form of Transbaikalian charr. Their unique feature is river spawning, which is not observed in any other charr population within BRZ. Due to special protection regime of the territory, which minimizes catch losses, several fish species maintain natural unaffected structure of their populations evidenced by the abundance of old fish. The population of lenok is represented by 19 age groups, the population of roach – by 15 groups and that of burbot – by 12 groups. Alternatively, populations of small-sized prey species such as minnow and sand sculpin, which are heavily influenced by numerous predators include fewer age groups than in other mountain lakes of BRZ.

Matveev Arkadiy Nikolaevich, Doctor of Science (Biology), Professor, Head of Chair, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, e-mail: matvbaikal@mail.ru 

Samusenok Vitaliy Petrovich, Candidate of Science (Biology), Associate Professor, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, e-mail: samusenk@mail.ru 

Yuriev Anatoliy Leonidovich, Candidate of Science (Biology), Associate Professor, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, e-mail: yuriev@bk.ru 

Vokin Aleksey Innokentyevich, Candidate of Science (Biology), Associate Professor, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, e-mail: vokin@bk.ru 

Samusenok Innokentiy Vitalyevich, Irkutsk State University, Leading Engineer, 1, K. Marx st., Irkutsk, 664003, Russian Federation, e-mail: aen_seidhe@mail.ru 

Alekseyev Sergey Sergeevich, Doctor of Science (Biology), Leading Research Scientist, Koltzov Institute of Developmental Biology RAS, 26, Vavilov st., Moscow, 119991, Russian Federation; A.N. Severtsov Institute of Ecology and Evolution RAS, 33, Leninski av., Moscow, 119071, Russian Federation, e-mail: alekseyev@mail.ru

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