Hematology and plasma biochemistry parameters are increasingly used for health assessment of elasmobranch species, both in clinical cases and preventive medicine.
Commonly used venipuncture sites in elasmobranchs include the ventral tail vein (or caudal vein), which can be approached laterally or ventrally in most animals under 90 kg, and the posterior cardinal veins, which can be accessed just caudolateral to either dorsal fin. In all elasmobranchs, the samples can be placed into dry heparin. In sharks, dry EDTA may be used, but dry or wet EDTA should not be used in batoids due to rapid hemolysis.
Several blood smears should always be made immediately and air-dried. If the blood is collected in heparin, the hematology must be processed immediately due to thrombocyte aggregation. Due to limited stability of the leukocytes in EDTA, blood collected in EDTA should be processed within 5 hr if refrigerated. Capillary tubes should be centrifuged for more than 5 min at 11,000 g for PCV measurements.1 Red blood cell counts appear more variable.1 Natt-Herrick is the preferred technique for total RBC and WBC counts, and is described, along with WBC differentials, elsewhere.1,2 It should be noted that nomenclature of some cell morphologies remains confusing, particularly granulocytes, and the clinical significance of the cell types has not been fully elucidated. Hematology results will vary depending on sample handling, technologist, taxonomy, age, environmental parameters including time of year, and pathology, so it remains useful to have baseline values for individual collection animals.
The plasma should be refrigerated, or frozen if analysis is delayed beyond 24 hr. Due to their osmoregulatory mechanisms, elasmobranchs have a plasma osmolality of 800–1,100 mOsm/kg, made up primarily of urea, trimethylamine oxides, sodium, and chloride. This will cause an increase in total solids as read by a refractometer when compared to colorimetric assays. Plasma samples will need to be diluted 1:10 for measurement of urea nitrogen and 1:2 for sodium and chloride. It may be useful to run blood gases and lactate levels in elasmobranchs.
At the National Aquarium in Baltimore, blood results have been closely tracked in sand tiger sharks (Carcharias taurus), sandbar sharks (Carcharhinus plumbeus), common nurse sharks (Ginglymostoma cirratum), southern stingrays (Dasyatis americana), and roughtail stingrays (Dasyatis centroura). Although some baseline values are available in the literature,1,3,4 it remains more useful to monitor and track blood results of collection animals in-house, and this is becoming increasingly common in many facilities.
1. Arnold JE. 2005. Hematology of the sandbar shark, Carcharhinus plumbeus: standardization of complete blood count techniques for elasmobranchs. Vet. Clin. Pathol. 34(2):115–23.
2. Old JM, C Huveneers. 2006. Morphology of the blood cells from three species of wobbegong sharks (Orectolobus species) on the East coast of New South Wales. Zoo Biol. 25:73–82.
3. Harms CA, T Ross, AI Segars. 2002. Plasma biochemistry reference values of wild bonnethead sharks, Sphyrna tiburo. Vet. Clin. Pathol. 31(3):111–115.
4. Cain DK, CA Harms, AI Segars. 2004. Plasma biochemistry reference values of wild-caught southern stingrays (Dasyatis americana). J. Zoo Wildl. Med. 35:471–6.