—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.

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.

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.

A nutritious diet is one of the most important factors in the successful management of captive animals. Basic methods for selecting diets for marine mammals have been described in the literature, yet methods developed for certain marine mammal species kept under specific conditions are quite rare. The diets of three male and two female spotted seals, Phoca largha Pallas, 1811, kept in sea pens at the Primorsky Aquarium, Branch of the National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences (Vladivostok, Russia), are discussed in the article. The diets were formulated based on the natural biological processes of this species in the wild. Information on them has been obtained from our own observations and from literature sources. Based on individual needs, adjustments have been made to the diets of the spotted seals, including pregnant and lactating females. The main food items of the spotted seals were Pacific herring, Clupea pallasii, Atka mackerel, Pleurogrammus monopterygius, commander squid, Berryteuthis magister, pink salmon, Oncorhynchus gorbuscha, chum salmon, Oncorhynchus keta, char, Salvelinus sp., capelin, Mallotus villosus, and shrimp, Pandalus sp. It has been found that the physiological status of the animals (molting, reproductive status, sex, and age) directly influences the qualitative and quantitative parameters of food intake. The diet and body weight of the spotted seals were significantly influenced by seasonal changes (water and air temperature and natural biological rhythms). These data can be used for selection of optimal feeding of P. largha.