Establishing leukocyte reference values in seven wild-caught shark species 2259588

Abstract Introduction Immune assessment in wildlife populations is challenging. Peripheral blood sampling is a non-invasive approach in understudied elasmobranch populations. However, hematological reference values are scarce for most shark species, limiting veterinary and conservation applications. This study establishes reference intervals for differential leukocyte counts across seven wild-caught shark species. Methods Peripheral blood smears from Carcharhinus limbatus (blacktip), C. acronotus (blacknose), C. plumbeus (sandbar), C. leucas (bull), C. perezi (Caribbean reef), Negaprion brevirostris (lemon), and Galeocerdo cuvier (tiger) were analyzed. Wright—Giemsa—stained leukocytes were classified morphologically as lymphocytes, neutrophils, coarse eosinophilic granulocytes (CEG), fine eosinophilic granulocytes (FEG), monocytes, and basophils. Counts were conducted (100 cells/slide) in triplicate per individual, and morphometric measurements were conducted using image analysis software. Results Leukocyte profiles varied across species and were dominated by lymphocytes with consistently low monocyte and basophil frequencies. Granulocyte to lymphocyte (GLR) ratios were within a narrow range, supporting GLR as a useful hematological biomarker. Substantial differences in granulocyte morphology were observed even among closely related species. C. limbatus exhibited lymphocyte predominance with balanced granulocyte subtypes. N. brevirostris showed comparatively few immature cells. Some species (C. leucas and G. cuvier) displayed elevated granulocyte ratios, which may be important considerations in evaluating immunological responsiveness to environmental stressors. Conclusion This study presents the first leukocyte reference intervals established from multiple species of wild-caught sharks. Results reveal interspecific variability in leukocyte distribution and establish essential hematological baselines for health assessment and conservation monitoring. Funding Source This research was supported by the University of Miami (UM) Shark Research and Conservation Program and the Disney Wildlife Conservation Fund; no other funding sources were involved. Topic Categories Veterinary and Comparative Immunology (VET)