—Blood cells of harbor seals, Phoca vitulina Linnaeus, 1758, from the Commander Islands population have been characterized in detail for the first time. Data on the composition, size, and ratio of red blood cells (RBCs), white blood cells (WBCs), and platelets in the peripheral blood of immature and mature seals are provided. A micrograph library for all types of peripheral blood cells of harbor seal is presented. The blood cell morphology of this seal generally corresponds to that of other pinniped species; however, neutrophils with Döhle bodies, reactive lymphocytes, and hypersegmented neutrophils have been found in blood films. Increased numbers of eosinophils (10–25%) have been recorded from the WBC differential counts of all examined seals. Mature seals had higher numbers of eosinophils (p = 0.04) and large lymphocytes (p = 0.005); immature seals had higher numbers of monocytes (p = 0.04) and Howell–Jolly bodies in RBCs (p = 0.03). Microfilariae and nucleated RBCs were observed in blood films of two mature seals.

Studying the blood cell morphology of marine mammals provides an opportunity to elucidate the physiological mechanisms of adaptive changes associated with the aquatic habitat that occur at the cellular level, as well as adaptations to changing environmental conditions and under various physiological and pathological processes. The Baikal seal [Pusa sibirica (family Phocidae)] is endemic to the freshwater Lake Baikal, but comprehensive hematology data are not available. We studied the morphological features of blood cells of twelve clinically normal, adult Baikal seals (n = 6 males, n = 6 females) from two oceanariums under professional care for eight years. The morphology of mature and immature erythrocytes and inclusions are described. The blood of Baikal seals is characterized by the presence of erythrocytes with a size of 8.2 ± 0.6 µm; Howell–Jolly bodies were rarely observed, the number of reticulocytes ranged from 4.1 to 93.1 × 10⁹/L, and nucleated erythrocytes were absent. The morphological features of neutrophils, eosinophils, basophils, and platelets were described. Inter-individual and sex differences in the counts of basophils, platelets, red blood cells, and levels of hemoglobin, the mean corpuscular volume, and the mean corpuscular hemoglobin concentration were statistically observed. The results could be useful for Baikal seal veterinary care, immune response research, and comparative studies with other pinnipeds.

Clinical blood analysis, combined with cytomorphological examination is an important diagnostic tool for assessing the physiological state of animals. The cytomorphological features of blood cells have been described for terrestrial mammals, and well-illustrated veterinary atlases have been created, in which normal and pathological forms of animal blood cells are displayed. However, such information is virtually nonexistent for marine mammals. In this article, we present the results of a study of the morphology of the blood cells of the beluga (also known as “white”) whale Delphinapterus leucas, obtained by supravital staining of blood smear preparations with Brilliant Cresyl Blue, Methylene Blue, and utilizing the standard Romanowsky–Giemsa staining technique. We describe the main types of blood cells of marine mammals: erythrocytes, segmented neutrophils, eosinophils, monocytes, lymphocytes, and band neutrophils, as well as rare basophils.

The invasion of bivalves by parasitic microalgae Coccomyxa is widespread and causes pathologies and dysfunctions of the organs, especially in the most valuable products: the mantle and the muscle. The pathogenesis of the disease remains completely unknown. In this study, based on a macroscopic examination of Modiolus kurilensis and microalgae count in each infected individual, four stages of disease development with characteristic pathognomonic symptoms were described. During the progression of the disease, the concentration of alkaline phosphatase, glucose, calcium, hemolytic and agglutinating activities, number of basophils, eosinophils, phagocytes, and cells with reactive oxygen species increased in the hemolymph, while number of agranulocytes, cells with lysosomes, dead hemocytes, total protein concentration, as well as the weight of mollusks decreased. In the nephridia and digestive gland, necrosis, invasion of Nematopsis sp., hemocyte infiltration, and fibrosis increased. The ratio of changed tubules and occurrence of granulocytomas increased in the digestive gland, while the base membrane, nephrocytes and concretions changed in the nephridia. This study helps establish the variability of these parameters under normal conditions and their alteration during the disease. Moreover, these findings can be used for veterinary monitoring of the state of bivalves in natural and aquaculture populations.