Potential Hematological and Biochemical Indicators of Stress in Free-Ranging Desert Tortoises and Captive Tortoises Exposed to a Hydric Stress Gradient

Hematologic and plasma biochemical parameters were monitored in free-ranging desert tortoises, Gopherus agassizii, near Las Vegas, NV and on a population of captive tortoises maintained in 4 ha pens with natural physiography and vegetation and subjected to varying levels of water supplementation to mimic different levels of hydric stress. Significant increases in plasma electrolyte and urea nitrogen concentrations and white blood cell counts (compared to free-ranging and water-supplemented, captive animals) occurred in captive animals without water supplementation. Differences in electrolytes and BUN among treatments were consistent with altered water balance. Free-ranging animals received no supplemental water. Blood profiles from free-ranging animals, however, more closely resembled profiles from captive animals that received supplemental water than profiles from animals that did not receive supplemental water. Captivity, thus, altered blood profiles in a manner similar to that seen with decreased water availability. The electrolyte, urea nitrogen, and white blood cell differences among water supplementation treatments, while significant, were not sufficient to distinguish among animals from different treatments. No reliably predictive indicators of water stress-or other stresses-were found. Several biochemical assays suggested specific stresses (other than water stress) which some of the tortoises faced. We suggest that blood profiles might be more profitably used to search for specific hypothesized stressors in populations rather than as assays of unspecified generic stress on populations of tortoises.