SREL Reprint #2138





Estimating Energy Metabolism of Goldfish (Carassius auratus) and Southern Toads (Bufo terrestris) from 86 Rb Elimination Rates


I evaluated the potential use of 86Rb elimination rate constants (86Rb kb's) as a predictor of oxygen consumption rates (Vo2's) for two ectotherms: the goldfish (Carassius auratus) and the southern toad (Bufo terrestris). I injected the goldfish intraperitoneally with 86Rb and measured the amount of the radionuclide remaining in the fish every 2-4 d for 14-28 d (eight measurements/treatment). I gave the toads subcutaneous injections of 86Rb and measured the remaining radionuclide every 3-4 d for 22 d (seven measurements/treatment). I measured 'Vo2's and 86Rb kb's of C. auratus at five temperatures (10.0, 12.9, 17.0, 21.2, and 24.0 C), salinities (280, 800, 1550, 2300, and 2800 µM each of Na+, K+, and Cl -), and food intake rates [0, 41, 100, 159, and 200 mg (dry) every 2 d] to determine the sensitivity of this method to environmental conditions. I measured Vo2's and 86Rb kb's of B. terrestris at 20.0 and 27.5 C., and assessed the sensitivity of the k. estimates to sampling interval by comparing simulated 3-point (10-12 d between measurements) and 2-point (22 d between measurements) elimination curves. Elimination curves were best described by a single exponential model. Carassius 86Rbkb's increased with temperature and salinity, decreased with increased body mass, and were not significantly affected by food intake rate. Bufo 86Rb kb's increased with temperature. There were significant relationships between Vo,'s and 86Rb kb's in both species, but this relationship lacked sufficient predictability (rl < 0.20) to permit accurate estimates of C. auratus energy metabolism. However, the relationship between Vo,'s and 86Rb kb's in B. terrestris was sufficiently predictive (rl = 0.68) to suggest that this method might be used to estimate FMRs of amphibians. Comparisons of the B. terrestris 86Rb kb's with 2-point and 3-point elimination curves indicated that relatively infrequent recaptures of individuals would be sufficient for field application of this method.

SREL Reprint #2138

Peters, E.L. 1996. Estimating the energy metabolism of goldfish (Carassius auratus) and southern toads (Bufo terrestris) from 86Rb elimination rates. Copeia 4:791-804.

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