The gray whale (Eschrichtius robustus Lilljeborg, 1861) peripheral blood cells: the first morphological and cytochemical study.

This study provides the first morphological and cytochemical characterization of peripheral blood cells in the gray whale (Eschrichtius robustus). Blood samples were collected post-mortem from 30 wild whales (23 immature, 7 mature; 17 females, 13 males) harvested by Native people of Chukotka (Chukchi and Inuit) during traditional subsistence hunts under Russian-established quotas. Stomach fullness, blubber thickness, entanglement scars, and parasite load were recorded. Leukocyte differential counts showed wide individual variation: band neutrophils, 0–16%; segmented neutrophils, 19–70%; lymphocytes, 17–69%; immature eosinophils, 0–8%; and mature eosinophils, 0–18%. Nucleated red blood cells (nRBCs) were observed in some individuals (up to 15 per 100 leukocytes), as were Howell–Jolly bodies in red blood cells (RBCs) (1–167 per 100 leukocytes) and macrothrombocytes (up to 32 per 100 leukocytes). Cytochemical staining revealed strong glycogen (PAS) positivity in neutrophils, eosinophils, and platelets, and moderate positivity in monocytes. Phospholipid (SBB) staining was strong in eosinophils and variable in neutrophils and monocytes. LUNA and Luxol Fast Blue (LFB) staining were specific to eosinophil granules. Given post-mortem sampling, the absence of absolute cell counts, and the lack of live-animal reference data, these findings should be interpreted as a descriptive morphological baseline rather than indicators of health or disease. This study contributes fundamental data for future comparative research on mysticete hematology.