Functional diploid Acipenser ruthenus, functional tetraploid Acipenser gueldenstaedtii and functional hexaploid Acipenser brevirostrum juveniles were sampled monthly for one year, and the white blood cell indicators were determined. The total number of leukocytes (TL) was 40.93 ± 17.24 × 10⁹/l for the diploids, 20.63 ± 11.20 × 10⁹/l for the tetraploids, 14.13 ± 7.72 × 10⁹/l for the hexaploids. The TL decreased with an increasing ploidy level. The highest number of leukocytes was reached during September and October for A. ruthenus and A. brevirostrum, from October to January for A. gueldenstaedtii (a statistically significant finding). The lymphocytes dominated (76.89–80.14%) in the differential counts and were found to be reduced in June and July in each group. Granulocytes were represented by neutrophils and eosinophils. Counting from all the leukocytes, the neutrophils represented 13.0–18.7% and eosinophils represented 5.7–6.1%. Increasing number of nuclear segments in the granulocytes was dependent on the increasing ploidy level. Nuclear segmentation in the lymphocytes was a common finding in higher ploidy level groups. The data suggest a significant effect of ploidy level on the total number of leukocytes and morphological nuclear changes in the granulocytes and lymphocytes. The seasonal variation in the differential leukocyte counts depends on the species and the influence of various external conditions rather than the ploidy level.