Metabolic rates in an anadromous clupeid, the American shad (Alosa sapidissima)

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of s peeds (1.0-2.3 body lengths (BL) s(-1), 13-24 degrees C). Metabolic rate (M -O2) was logarithmically related to swimming speed (B1 s(-1); r(2) = 0.41, slope = 0.23 +/- 0.037) and tailbeat frequency (beats x min(-1); r(2) = 0.5 2, slope = 0.003 +/- 0.0003). Temperature had a significant effect on metab olic rate (r(2) = 0.41) with a Q(10) of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine t riethiodide, ranged from 2.2-6.2 mmolO(2) kg(-1) h(-1) and scaled with mass (W) such that SMR = 4.0 (+/- 0.03)W0.695(+/-0.15). Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provide s a good estimate of SMR in this species, given the differences in basal ac tivity monitored by the two methods. Overall, American shad metabolic rates (M-O2 and SMR) were intermediate between salmonids and fast-swimming perci forms, including tunas, and may be a result of evolutionary adaptation to t heir active pelagic, schooling life history. This study demonstrates variab ility in metabolic strategy among anadromous fishes that may be important t o understanding the relative success of different migratory species under v arying environmental conditions.