Secor and Gunderson: Effects of hypoxia and temperature on Acipenser oxyrinchus 
607 
Table 2 
Replicate tank deaths during the nested survival and growth experiment. Experiments are labeled according to the temperature 
treatment and whether tanks were sealed or unsealed (unsealed tanks permitted access by sturgeon to surface water). Dissolved 
oxygen (DO) levels, low and high, refer to prescribed levels of 3 mg/L and 7 mg/L, respectively. Rep. = replicate(s). 
Experiment 
DO 
level 
Rep. 
Experimental day 
Survival 
(%) 
1 
2 
3 
4 
5 
6 
7 8 9 10 
26°C unsealed 1 
Low 
1 
6 
1 
1 
0 
2 
2 
4 
2 
0 
3 
4 
1 
2 
1 
0 
4 
1 
1 
1 1 
50 
26°C unsealed 2 
High 
1 
100 
2 
100 
3 
100 
4 
100 
26°C sealed 
Low 
1 
8 
0 
2 
7 
1 
0 
High 
1 
100 
2 
100 
19°C unsealed 
Low 
1 
1 
1 
75 
2 
1 
1 
75 
High 
1 
100 
2 
100 
19°C sealed 
Low 
1 
1 
88 
2 
1 
1 
75 
High 
1 
100 
2 
100 
(mean=78.3% survival). No significant difference was 
found in overall survival rate between sealed and 
unsealed tanks (P=0.54). In unsealed tanks, deaths 
were distributed throughout the 10-d experimental 
period. In the 26°C sealed-hypoxic level tanks, all 
individuals succumbed within the first 30 hours of 
the experiment. Moribund sturgeon were observed 
at the air-water interface in unsealed tanks, or just 
below the lid in sealed tanks. Fin margins of dead 
individuals were perfused with blood, an indicator 
of oxygen deprivation (Jobling, 1995). 
Growth 
Across replicates, growth rates ranged in weight from 
0.3% to 5.1% per day (Table 3). Sturgeon experienced 
positive growth in weight and length under all ex- 
perimental conditions. Initial mean weights and 
lengths varied substantially among experiments; 
range was 10.94 to 69.20 g in weight and 14.59 to 
26.60 cm in length. Absolute growth in weight was 
positively related to initial size (regression analysis; 
P<0.01); tanks with fish having initial mean weights 
greater than 50 g showed the highest absolute growth 
rates (>1.0 mg/d). Because initial size covaried with 
growth rate, initial weight was used as a covariate 
in statistical analyses of treatment effects. 
Analysis of variance of instantaneous growth rate 
showed significant effects due to surface access and 
oxygen level (Table 4); temperature, replicate, and 
individual fish did not explain significant variance, 
although at 7 mg/L DO there was a trend for lower 
growth rates at 26°C than at 19°C (Fig. 2, Table 3). 
Mean growth rates were 2.9 times less at 3 mg/L 
(1.27%/d) than at 7 mg/L (3.62%/d). Sealed tanks 
showed consistently lower growth rates than those 
with surface access. The effect was greatest at 3 mg/L 
oxygen. Only 0.3%/d weight-specific growth was ob- 
served in the 19°C sealed tanks, and all fish perished 
before growth determinations could be made in the 
26°C sealed tanks. Absolute growth in weight was 
significantly affected by surface access, temperature, 
surface access in combination with temperature in- 
teraction, and by oxygen level. Absolute growth rate 
was higher when surface access was allowed and at 
the higher DO level; absolute growth rate was in- 
versely related to temperature. 
Respiration 
Respiration rates measured over the entire experi- 
ment ranged from 0.05 to 0.55 mg 0,>/(g-h) (Fig. 3). 
Respiration rates were normally distributed for the 
high oxygen treatment with a mean of 0.245 ± 0.013 
