Seasonal dynamics of antennual bristles number (ABN), cephalothorax length (CL), caudal chaeta length (CCL) and the fifth pair swimming legs length (FPSLL) in females and males E. baicalensis VI, V and IV copepodytes stages was study. Under this, throughout sex dimorphism CCL in adult females and FPSLL in adult males were not accessed. It was shown, that, with except ABN in adult males and specimen both sexes of V copepodytes stages, seasonal dynamics was statistical significance. On every trait and age-sex category a seasonal changing have a specific character. The access of phenotypic structure presence of two classes (L and H) on ABN and three classes (L, M and H) on morphometric traits were shown. L-classes were consisted the specimen with low values of trait, M-classes – with medium and H-classes – with high. Seasonal dynamics on ABN was determined by transformation of individual number in L- and H-classes, on morphometric traits individual number in M-class a play important rule. A possibility of influence on obtaining seasonal dynamics natural selection on set quantitative morphological traits was discussed.