Abstract
Elasmobranchs are a basal phylogenetic group and possess an immune system comparable to the mammalian model, which make them great model organisms for comparing the evolution of the immune system. Shark leukocytes are composed of lymphocytes, granulocytes (FEGs, CEGs, basophils, neutrophils), and monocytes. Most of these cells have similar mammalian counterparts and are suspected to perform comparable immune functions in Elasmobranchs. Elasmobranch health can be used as bioindicators of environmental pollution, which is why accurately assessing their health is so important. Similar to other vertebrates, sharks can exhibit primary blood disorders that cause abnormalities that can be detected in blood-base indicators. Common blood tests that are used in health assessments include the granulocyte-lymphocyte ratio (GLR) and complete blood count (CBC). Unfortunately, reference intervals (RI) have not been established for sharks and the health of both wild and captive populations are not being properly assessed. The objective of this study is to define morphological characteristics of leukocytes that will enable GLR calculation and to derive a cell count factor (CCF) using values from literature to estimate CBC. The three shark species compared during this study were bull sharks (Carcharhinus leucas), blacknose sharks (Carcharhinus acronotus), and blacktip sharks (Carcharhinus limbatus). A 30 sharks sample size, with 10 individuals per species was observed. Peripheral blood smears were used to determine immune cell type differentials per 100 cells and an estimated total leukocyte count. Light microscopy under oil immersion at a magnification of 100x was used for cell type differentials and a magnification of 40x was used to estimated total leukocyte count. The mean GLRs for C. leucas, C. acronotus, and C. limbatus were 0.4376, 0.4380, and 0.4592, respectively. The mean leukocyte count at 40x for C. leucas, C. acronotus, and C. limbatus was 86.09, 86.05, and 82.51, respectively. For both C. leucas and C. acronotus, the minimum and maximum CCF values were 5.81 x 104 and 1.16 x 105, respectively. For C. limbatus, the minimum and maximum CCF values were 6.05 x 104 and 1.21 x 105, respectively. The consistency and narrow range of values for GLR and CCF across all three study species indicate that these tests are reliable indicators of health. Findings also suggest that reliable RI can be established for GLR and CCF for these species in the future and have the potential to be applied to other species within Carcharhinidae.