Secor and Gunderson: Effects of hypoxia and temperature on Acipenser oxyrinchus 
609 
3 mg/L 
7 mg/L 
3 mg/L 
7 mg/L 
Figure 2 
Effects of dissolved oxygen concentration on instantaneous growth rates 
in weight (per day) (mean ± 95% confidence interval) of young-of-the-year 
Atlantic sturgeon at two temperatures and different tank configurations. 
Stippled bars indicate treatments denying surface access. Replicate tanks 
were combined for each treatment level comination. The asterisk indi- 
cates that complete mortality occurred for that treatment. 
mg Og/fg-h). In relation to the high oxy- 
gen treatment, hypoxic oxygen treatment 
respiration rates were skewed towards 
lower rates with a mean of 0.174 ±0.016 
mg OgAg-h). Two individual tank respi- 
ration rates for the hypoxic treatment 
were exceptionally high (Fig. 3). These 
data were measured at 0 hours from 
tanks at 19°C and 26°C and may have 
reflected an insufficiently long period 
of acclimation prior to the experiments. 
Therefore, we chose to exclude measures 
taken at 0 hours in the analysis of vari- 
ance on respiration rates. 
Respiration rates were significantly 
influenced by oxygen level CP=0.001), by 
the interactions between temperature 
and oxygen (P-0.04), and by the inter- 
action among temperature, oxygen, and 
replicate (P=0.04). Mean respiration 
rates were 0.187 ± 0.012 and 0.247 ± 
0.015 mg O^lg-h) under hypoxia and 
normoxia, respectively (Table 1). At 
high oxygen levels, 26°C respiration 
rates (mean=0.281 ±0.023 mg 0 I? /(g-h)) 
tended to be higher than 19°C respira- 
tion rates (mean-0.210 ±0.021 mg O ^ 
(g h)). However, the converse was true 
at hypoxic levels; mean respiration rate 
at 26°C (0.136 ±0.027 mg O^g-h)) was 
significantly lower than at 19°C (0.212 ±0.021 mg 
OgAg-h)). For all but the 26°C and hypoxic-level com- 
bination, replicate rates were similar. Respiration for 
the second replicate for the 26°C and hypoxic-level 
combination was substantially lower than other rep- 
licates that may have produced the significant in- 
teraction among temperature, oxygen, and replicate 
factors in the analysis of variance. In a procedure to 
reduce bias associated with deviations of actual in- 
flow DO levels from those prescribed, an analysis of 
variance was conducted for which the inflow oxygen 
concentration was a covariate. After viariance asso- 
ciated with individual tank DO conditions was re- 
moved, the effect of oxygen level (high or low) re- 
mained significant (P=0.04). 
Discussion 
Juvenile Atlantic sturgeon were vulnerable to con- 
ditions of high temperature and low oxygen. In five 
out of six replicates (sealed and unsealed tanks com- 
bined) at 26°C and -3 mg/L DO, all juveniles died. 
All sturgeon that died showed a perfusion of blood 
along the margins of their fins, indicative of oxygen 
deprivation (Jobling, 1995). Reduced oxygen levels 
resulted in a threefold reduction in growth rate and 
a 50% reduction in routine respiration rate. At 19°C, 
respiration rates were similar between hypoxic and 
normoxic treatments. But, at the 26°C hypoxic treat- 
ment, mean respiration rates dropped below 2 mg 
0 9 /(g h) and all sturgeon died. We speculate that 
these fish were unable to supply sufficient oxygen to 
their tissues at this level of reduced respiration. 
Despite reduced survival and respiration in condi- 
tions of low dissolved oxygen, feeding continued and 
fish grew. Apparently, Atlantic sturgeon were able to 
reduce activity but still feed and allocate some en- 
ergy to growth. In unsealed tanks, weight gain 
ranged from 1.1% to 2.9%, and from 3.6% to 5.0% 
body weight per day, at ~3 and ~7 mg O./L, respec- 
tively. Cech et al. (1984) also observed continued 
growth by juvenile white sturgeon ( Acipenser 
transmontanus) (ca. 0.5 to 5 g) under conditions of 
hypoxia. Daily weight-specific growth rates of white 
sturgeon varied between 1.6% ( 15°C) and 2.9% (25°C) 
under normoxic conditions and between 0.6% (15°C) 
and 2.3% (25°C) under hypoxic conditions. Growth 
rates measured by Cech et al. (1984) under hypoxia 
were substantially higher than those that we oh- 
