This review summarizes and analyzes data on the threespine stickleback Gasterosteus aculeatus L. of the White Sea, which is currently the most abundant fish in the region and, therefore, plays an important role in inshore and offshore communities. The threespine stickleback was abundant in the 1920s–1940s; its numbers declined significantly between the late 1960s and late 1990s and have increased again since then, showing a positive correlation with water temperature. In order to reveal the mechanisms of changes in the population of this species and to assess its role in the marine ecosystems, various aspects of the population biology of the species (interannual and seasonal population dynamics, spatial heterogeneity, age and sex structure, lipid and fatty acid status, homing, and fluctuating asymmetry), as well as its interactions with other organisms (feeding characteristics of adults and juveniles, role in feeding predatory fish, association with eelgrass, parasite composition and spatial distribution, and relationships with competing species) are analyzed.

Sexual dimorphism (SD) in the threespine stickleback Gasterosteus aculeatus reflects the different roles of the sexes in reproduction and their adaptations to different ecological niches. We quantified SD in one population of marine stickleback from the White Sea, collected during the spawning period from three spawning grounds, each at a distance of 5 km or less from the others. We used a landmark-based approach to quantify variation in 44 morphometric linear traits. In total, 749 females and 693 males were analyzed. In males, anterior body parts are larger — the base of the caudal fin and armor structures such as the first and second dorsal spines and the pelvic spine. Females have larger posterior bodies — the abdomen, pelvic girdle and the third dorsal spine. The SD of caudal body parts exhibits complex patterns. In White Sea threespine stickleback, SD patterns are generally similar to other populations of the species, but more often show male-biased patterns. Female-biased size SD may be associated with the female biased sex ratio of White Sea stickleback. threespine stickleback, sexual dimorphism, morphological variation, body shape, body size, White Sea