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Fishery Bulletin 11 7(4) 
that the gradient in partial pressure of oxygen (P0 2 ), 
rather than in DO concentration, drives the rate of oxy¬ 
gen diffusion and, therefore, oxygen uptake for an organ¬ 
ism (Farrell and Richards, 2009). The ability of water to 
hold oxygen decreases with increasing temperature, but 
the P0 2 at any given oxygen concentration increases with 
temperature. 
Thermal tolerance of striped bass varies by several 
degrees depending on experimental methodology, differ¬ 
ences among fish stocks, geographic location, age of fish, 
and the ranges of water temperature and oxygen concen¬ 
tration available to the fish (Crance 3 ). Merriman (1941) 
reported a maximum thermal tolerance of 25-27°C on the 
basis of field distribution records in New England. How¬ 
ever, Tagatz 4 found that adult striped bass sampled in 
North Carolina tolerated temperatures of 0-30°C in the 
laboratory. Gift (1970) observed a median lethal tempera¬ 
ture of 31.5°C for adult striped bass sampled in New Jersey, 
acclimating them to 20°C and raising the temperature to 
the lethal level over a period of approximately 24 h. The 
same experimental procedure showed a higher tempera¬ 
ture tolerance for juvenile striped bass, with a median 
lethal temperature of 37°C. Likewise, Coutant et al. (1984) 
reported the optimum temperatures for juvenile striped 
bass (80-300 mm in total length [TL]) as 24-27°C, and 
Coutant and Carrol (1980) reported an optimal tempera¬ 
ture range of 20-24°C for larger juvenile striped bass 
(430-680 mm TL). These findings agree with the premise 
that juvenile striped bass are more tolerant of high tem¬ 
peratures than adults. 
Nearly all observations of physiological limits of striped 
bass have been on migratory northern populations (i.e., 
those above Cape Hatteras), which likely have different 
physiological tolerances than southern populations (i.e., 
those below Cape Hatteras) because of their different life 
history. Southern populations of striped bass are essen¬ 
tially non-migratory (Greene et al. 2 ). In South Carolina, 
populations of striped bass are small, reproductively 
isolated, and exist either in inland impoundments or in 
coastal rivers (Bulak et al., 2004; Sessions et al. 5 ). The 
results of field studies exploring habitat preferences in 
inland impoundments indicate that striped bass choose 
habitats with temperatures of 20-24°C during the sum¬ 
mer and occupy habitats with temperatures up to 26°C 
when a cooler habitat is unavailable (Schaffler et al., 2002; 
Young and Isely, 2002). However, the coastal rivers and 
estuaries that some southern populations inhabit do not 
have the degree of thermal refuge of inland impoundments. 
3 Crance, J. H. 1984. Habitat suitability index models and 
instream flow suitability curves: inland stocks of striped 
bass. U.S. Fish Wildl. Serv., Div. Biol. Serv. Res. Dev. FWS/ 
OBS-82/10.85, 63 p. [Available from website.] 
4 Tagatz, M. E. 1961. Tolerance of striped bass and American shad 
to changes of temperature and salinity. U.S. Fish Wildl. Serv., 
Spec. Sci. Rep. Fish. 388, 8 p. [Available from website.] 
5 Sessions, F., S. Lamprecht, J. Bettinger, J. Bulak, and M. Scott. 
2015. Striped bass .In South Carolina’s state wildlife action plan 
(SWAP) 2015. Suppl. vol.: species of conservation concern. South 
Carolina Dep. Nat. Resour., Columbia, SC. [Available from 
website.] 
In a coastal river of South Carolina, Bjorgo et al. (2000) 
observed that striped bass chose habitats with tempera¬ 
tures of 25-27°C during periods when downstream habi¬ 
tats were as much as 5°C higher. 
Striped bass will select habitats with water that is 
warmer than their preferred range when DO concentra¬ 
tion is low in cooler water (Farquhar and Gutreuter, 1989). 
During summer, when temperatures are highest and DO 
levels are lowest, striped bass select the coolest habitat 
available with DO concentrations over 2.0-2.5 mg/L (Zale 
et al., 1990). Water temperatures in summer (June-August) 
at our study site, the Ashley River in South Carolina, have 
been 19-33°C (M. Denson, unpubl. data; Fig. 1), with tem¬ 
peratures of 24-31°C being the most frequent (80% of 
observations). Concentrations of DO typically range from 
3.5 to 5.5 mg/L during the summer, with levels <4.0 mg/L 
for 28% of observations and levels <3.0 mg/L for 1% of 
observations. Tolerance of both high temperatures and low 
DO concentrations is likely important to survival of striped 
bass in the coastal rivers and estuaries of the southeastern 
United States. 
Temperature is the principal controlling factor of met¬ 
abolic demand; within an ectotherm’s temperature range, 
metabolism is expected to increase 2-3 fold for every 10°C 
increase in temperature (Hochachka and Somero, 2002). 
Aerobic metabolic scope (AMS) is defined as the mathemati¬ 
cal difference between the maximum metabolic rate (MMR) 
and the standard metabolic rate (SMR) (Fry, 1947, 1971). 
Aerobic metabolic scope represents the metabolic confines 
within which all aerobic energetic processes (e.g., somatic 
and gonadal growth, digestion, and activity) must be per¬ 
formed (Fry, 1947, 1971; Neill and Bryan, 1991; Lapointe 
et al., 2014). Although SMR increases with temperature 
(Fry and Hart, 1948), MMR levels off, or even decreases, 
when temperatures become too high (Fry and Hart, 1948; 
Portner and Knust, 2007). Therefore, at high tempera¬ 
tures, AMS is expected to decrease because of tissue oxygen 
demand outpacing oxygen supply from the environment 
(Portner, 2001,2002). Many studies have quantified AMS as 
a proxy for biological performance in a given environment 
(e.g., Portner and Knust, 2007; Farrell et al., 2008; Clark 
et al., 2011; Lapointe et al., 2014) and have found that the 
time it takes for a swimming fish to exhaust (i.e., exhaustion 
time) is positively correlated with AMS (Reidy et al., 2000; 
Metcalfe et al., 2016). 
This study is the first to examine the interactive 
effects of temperature and low DO concentration on aer¬ 
obic metabolism and swimming performance in southern 
stocks of striped bass. The objective of this study was 
to compare changes in AMS during acute exposure to 
hypoxic treatments (DO levels of 2.5, 3.0, and 4.0 mg/L) 
in striped bass that were acclimated and exercised at 
3 temperatures (20°C, 25°C, and 32°C). These tempera¬ 
tures span the range of the summer thermal regime 
in the Ashley River, and the DO levels mimic the lower 
end of DO concentrations observed in this river (Fig. 1). 
Although environmental P0 2 has a more direct effect on 
fish oxygen uptake than environmental oxygen concen¬ 
tration, specific oxygen concentrations were chosen on 
