LAUSR

Detailed morphological description of Cherskii’s sculpin Cottus czerskii (Cottidae) is conducted. Main directions of intraspecific variation of the phenotype are described. The ontogenetic variation of 24 of 31 morphometric characters is registered. The characters are subdivided into four categories based on the features of their variation and degree of ontogenetic allometry. Sexual dimorphism is observed based on the following characters: length of the rays of the pelvic fin, length of the anal fin base, depth of the anal fin, antedorsal distance, and head depth. A latitudinal increase of the fin rays in the anal and pectoral fins from the southern to the northern parts of the biogeographic range is registered. The relationships of the species with other representatives of the family Cottidae are discussed based on the comparative analysis of morphological and ecological features. A complex of plesiomorphic morphological and ecological characteristics, which are similar to those in more ancient catadromous, brackish-water, and marine forms, is described. Based on morphological characters, C. czerskii is substantially similar to C. hangiongensis.