HEMOLYMPH CYTOLOGY, CELL COUNT, AND ELECTROLYTE REFERENCE VALUES IN CAMEROON RED TARANTULA (Hysterocrates gigas) Cédric B. Larouche, DVM, IPSAV,1,2 Janet Beeler-Marfisi, BA, DVM, DVSc, Dipl ACVP,1 Lydia Attard, MSc,2 Nicole Nemeth, DVM, PhD, Dipl ACVP, 1 and Hugues Beaufrère, Dr.Med.Vet., PhD, Dipl ACZM, Dipl ECZM (Avian), Dipl ABVP (Avian)1 1Ontario Veterinary College, University of Guelph, Guelph, ON, N1G 2W1 Canada; 2Toronto Zoo, Toronto, ON, M1B 5K7 Canada Abstract: Tarantulas of the family Theraphosidae are commonly kept as pets or display animals in zoological institutions. Over the last decade, requests for arachnid medicine have increased, but the range of diagnostic tests is limited (Pizzi, 2011). Hemolymph analysis could be an important tool to evaluate arachnid health. Ninety-three mature Cameroon red tarantulas (Hysterocrates gigas) from the Toronto zoo were used to collect 0.35 ml of hemolymph from the dorsal opisthosoma. Hemocytes were characterized and reference intervals were established for absolute and differential hemocyte counts and electrolyte values (Scherman, 1981; Friedrichs et al, 2012; Soares, et al, 2013; Bednaski et al, 2015). These results help support a more quantitative assessment and thus a better understanding of arachnid health. Objectives: 1. To characterize the circulating hemocytes in the Cameroon red tarantula. 2. To provide reference intervals for hemocyte absolute and differential counts, as well as for hemolymph electrolyte values in the Cameroon red tarantula. Conclusion: Hemocyte counts for the Cameroon red tarantula indicate that plasmatocytes are predominant; granulocytes are common while cyanocytes and prohemocytes are rare. The hemolymph electrolyte values are comparable to other tarantula species but differ from dog and cat blood such that tarantulas have higher sodium, chloride, and ionized calcium, while having lower potassium and glucose levels. Hemocyte characterization and counts as well as electrolyte values established in this study will aid in the health assessment of this species and others albeit limited as more such studies on different species are needed to be of more assistance. References: Bednaski AV, Trevisan-Silva D, Matsubara FH, et al. (2015) Characterization of Brown spider (Loxosceles intermedia) hemolymph: Cellular and biochemical analyses. Toxicon. 98:62-74. Friedrichs KR, Harr KE, Freeman KP, et al. (2012) ASVCP reference interval guidelines: determination of de novo reference intervals in veterinary species and other related topics. Vet Clin Pathol. 41(4):441-453. Pizzi R. Spiders. (2012) In: Lewbart GA, ed. Invertebrate Medicine. 2nd ed. Oxford, United Kingdom: Wiley-Blackwell; 187-221. Scherman RG. (1981) Chelicerates. In: Ratcliffe NA, Rowley AF, eds. Invertebrate Blood Cells. 1st ed. New York, NY: Academic Press Inc.; 1981:355-384. Soares T, Cavalcanti MGDS, Ferreira FRB, et al. (2013) Ultrastructural characterization of the hemocytes of Lasiodora sp. (Koch, 1850) (Araneae: Theraphosidae). Micron. 48:11- 16. .