SREL Reprint #2138
Estimating Energy Metabolism of Goldfish (Carassius
auratus) and Southern Toads (Bufo terrestris) from 86 Rb
Elimination Rates
ERIC L. PETERS
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.
