Hematology and Plasma Biochemistry in Whale Sharks (Rhincodon typus): Baseline Reference Intervals Based on Captivity Status, Blood Sampling Sites, and Handling Methods.

Abstract

This study aimed to establish reference intervals for red and white blood cell counts, hematocrit levels, mean corpuscular volume, and 25 key plasma biochemistry parameters in captive and wild whale sharks (Rhincodon typus). Blood samples were collected from the caudal vein (CV) and dorsal cutaneous vein (DCV) of 30 wild sharks caught in fixed nets off the Kochi Prefecture coast, Japan, and from 24 captive sharks between 2007-2023. Samples were obtained from restrained captive and wild sharks as well as unrestrained captive sharks trained for husbandry. Comparative analyses considered three factors: captivity status (wild vs. captive sharks under restraint), blood sampling sites (CV vs. DCV under restraint), and handling methods (DCV sampling under restrained vs. unrestrained conditions). Analysis of captivity status revealed significant differences in 12 of 29 parameters, with triglyceride levels significantly lower in wild sharks, possibly indicating nutritional deficiencies due to their prolonged migrations. Comparisons of blood sampling sites revealed significant differences in 11 parameters, including red and white blood cell counts and hematocrit levels, with most CV-derived parameters being higher than those from the DCV. A strong correlation (r > 0.7) was found between the CV and DCV for 19 parameters, indicating predictive values between these vessels. Additionally, the relationship between RBC, Ht, and MCV indicates that the RBC and MCV results may not be entirely reliable and should therefore be interpreted with caution. In the handling method comparison, eight parameters exhibited significant differences; specifically, aspartate aminotransferase, ammonia, and creatine phosphokinase levels were likely influenced by stress effects, including restraint-induced muscle damage. These findings emphasize the importance of unrestrained blood collection, facilitated through husbandry training, for accurate blood parameter evaluations. Integrating statistical results across the three studied factors allowed for the establishment of reference intervals, means, and medians for whale sharks, contributing to health management in captive sharks and conservation in wild populations.