Effects of Temperature and Nitrogenous Wastes on Survival and Growth of the Barton Springs Salamander Eurycea sosorum
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The Barton Springs Salamander (BSS), Eurycea sosorum, is a federally endangered obligate aquatic salamander found only in a few spring outflows located in a highly urbanized recreational area of Austin, Texas. The purpose of this study was to gain essential information regarding the physiological response of the BSS to thermal manipulations and three common aquatic nitrogenous toxins (ammonia, nitrite, and nitrate). All salamanders used in this study were produced at the San Marcos Aquatic Resource Center (U.S. Fish and Wildlife Service) as part of a captive breeding program. To examine thermal stressors, salamanders were subjected to a temperature increase of 0.5°C per day until a loss-of-righting response (LRR) was observed. Additionally, salamander growth was assessed following a 69 day trial in which young salamanders were reared at five different temperature treatments (nominal 15, 18, 21, 24 and 27°C). The cumulative ET50 of the LRR for the combined replicates observed in the BSS was 32.6 ± 0.24°C (mean ± SD). The optimal temperature for growth of the BSS for total length was estimated to be 18.3°C resulting in a 59.7 ± 21.09% increase in total length. To investigate the effects of nitrogenous wastes on the BSS, ninety-six hour median-lethal concentration (96-hour LC50) trials were conducted for un-ionized ammonia-N (UIA-N), nitrite-N, and nitrate-N. The 96-hour LC50 of UIA-N, nitrite-N, and nitrate-N to the BSS was 2.1 ± 0.19 mg/L, 27.7 ± 0.72 mg/L, and 851.1 ± 49.21 mg/L, respectively. These results will aid in the conservation, management, and ongoing efforts to culture the BSS in captivity.