Abstract

Knowing the estimated blood volume of a species is helpful in determining a safe maximum quantity of blood that can be withdrawn for clinical or diagnostic purposes, especially in smaller individuals. Occasional studies have been performed to determine blood volumes in teleost species, with highly variable results, but little is known about the blood volume of batoid elasmobranchs. Three southern stingrays (3.0) and three cownose rays (0.3) of roughly similar size (3.3–6.1 kg) were used to determine average blood volume of two batoid species with distinct ecological niches, benthic and pelagic, respectively.

Utilizing a long-standing technique of dye dilution, a known quantity of Evans blue dye was administered intravenously to each study animal. The dye was allowed to equilibrate through the circulation while the rays swam freely, and blood samples were collected at 30 minutes and 60 minutes after injection. The blood was centrifuged for plasma collection, and absorbance was measured at 620 nm using a benchtop spectrophotometer.

A standard curve was developed for each animal using plasma collected prior to injection of the dye with known concentrations of Evans blue dye added. The absorbance values obtained from plasma at the two time periods were then compared to the standard curve to calculate blood volume for each individual and species.

Acknowledgements

The authors thank Dr. Craig Harms and Dr. Brianne Phillips for assistance in sample collection, as well as the husbandry staffs of the North Carolina Aquarium at Pine Knoll Shores and the North Carolina Aquarium on Roanoke Island for their assistance with study procedures and care of the animals.