Hematology and blood pH reference intervals for wild Spiny Butterfly Rays (Gymnura altavela) in the Canary Islands

Abstract

Background: Despite the popularity of elasmobranchs in zoos and aquariums, data on hematological values for health monitoring remain limited, particularly for wild populations. In this study, reference intervals for key hematological parameters and blood pH were established from blood samples of 49 adult females of the Critically Endangered Spiny Butterfly Ray (Gymnura altavela) collected across three shallow beaches in the Canary Islands. Additional data were obtained from four adults maintained under human care. To our knowledge, this is the first report of hematological and blood pH reference intervals for free-ranging G. altavela. Results: Lymphocytes (56%) were the dominant leukocyte, followed by heterophils (23.6%), eosinophils (16.7%), monocytes (2%), neutrophils (1.1%), and basophils (0.2%). Median values included 356.6 10 cells/L for red blood cell count (RBC), 31.7 10 cells/L for white blood cell count (WBC), 28.2% for packed cell volume (PCV), and 8.1 g/dL for total plasma solids (TS). Blood pH averaged 7.25, rising to 7.38 with temperature correction. These values remained consistent across reproductive states and housing conditions, suggesting minimal physiological disruption. Conclusion: This study highlights the effectiveness of rapid, low-stress sampling and provides essential baseline data to support veterinary care and conservation strategies for G. altavela. Expanding future research with a larger sample size will enhance understanding of health variations by age, sex, and reproductive status.