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Fishery Bulletin 96(3), 1 998 
rate. Regeneration of the scute did not obscure the 
clip during the 10-d experiments. Six to eight juve- 
niles were placed in each experimental tank and fed 
the formulated diet (2-mm pellets) at 2.5% body weight 
per day. Fish were fed at 06:00, 10:00, 14:00, 18:00, 
and 20:00 h. Water quality was checked during feed- 
ing times and any remaining food or feces were siphoned 
prior to feeding. Food amounts were adjusted when 
mortalities occurred. On day 10 of the experiment, in- 
dividual weights and lengths were recorded. Weight- 
specific absolute and instantaneous growth rates were 
determined for the experimental period according to 
Ricker (1975). In instances where juveniles died before 
the end of the experiment, individuals surviving >3 days 
of experimental conditions were included in the analy- 
sis of treatment effects on growth. 
peratures. For the hypoxic treatments, oxygen was 
provided at significantly higher levels (P=0.001) at 26°C 
(4.09 ±0.07 mg/L) than at 19°C (2.51 ±0.05 mg/L). This 
was intentional because survival and growth experi- 
ments had shown that DO levels <3.5 mg/L in con- 
cert with high temperature were lethal. Despite this 
precaution, all fish at 26°C and at low oxygen level 
perished within 24 hours. At the high-level DO treat- 
ments, oxygen conditions were ca. 1 mg/L higher at 
19°C than at 26°C. Total biomass of the 7 fish per 
tank ranged from 157.6 to 248.2 grams (Table 1). 
Respiration (i.e. oxygen uptake) was estimated 
(Cech, 1990) as 
R = (M e - M c )/B 
Me.c = ((C/ ~ C 0 ) V 
Respiration experiment 
Respiration was estimated over a 42-h period for four 
combinations of temperature (19 or 26°C) and dis- 
solved oxygen (-3 or ~7 mg/L) each replicated once. 
Juveniles were acclimated for a 4-day period and 
starved 12 h prior to the start of respiration mea- 
sures. Seven juveniles were weighed (in water) and 
placed in each tank “respirometer.” The tanks were 
sealed (no air gap). Oxygen levels were maintained 
by aerating the head-tanks, rather than each experi- 
mental tank. There was no feeding during the 42-h 
experiments. Inflow and outflow temperature, salin- 
ity, oxygen content, and flow rate were measured in 
experimental and control “blank” tanks (Cech, 1990) 
at 06:00, 10:00, 14:00, 18:00 and 22:00. 
Experimental conditions of temperature were 
maintained within 1°C of the prescribed treatment 
level (19 or 26°C) (Table 1). Oxygen levels varied 
substantially from the prescribed levels between tem- 
where R 
M e.c 
B 
Ci 
C'c 
V 
weight-specific 0 2 consumption rate (mg 
0 2 /(g-h); 
0 2 consumption rate in experimental E 
or control C tanks (mg Og/h); 
combined wet weight (biomass) of stur- 
geon juveniles (g); 
0 2 concentration in inflowing water ( mg 
0 2 /L); 
0 2 concentration in outflowing water 
(mg 0 2 /L); and 
water flow rate (L/h). 
Results 
Survival 
Deaths were observed only in hypoxic treatments 
(Table 2). At hypoxic level, survival was substantially 
lower at 26°C (mean=6.3% survival) than at 19°C 
Table 1 
Replicate tank environmental conditions and respiration rates (mean ± standard error) for respiration experiment. Dissolved 
oxygen (DO) levels, low or high, refer to prescribed levels of 3 mg/L and 7 mg/L, respectively. Inflow oxygen and tank temperature 
refer to actual conditions provided to tanks. Biomass is the total initial weight of the seven sturgeon used in each replicate. 
Temperature 
level 
DO 
level 
Inflow oxygen 
mg/L 
Tank 
temperature 
Biomass 
(g) 
Respiration rate 
mg 0 2 /g h 
26°C 
Low 
3.762 + 0.163 
25.20 ± 0.04 
216.6 
0.175 ± 0.042 
4.436 ± 0.209 
25.34 ± 0.02 
181.3 
0.103 ± 0.030 
High 
6.310 ± 0.075 
25.54 ± 0.02 
188.1 
0.245 ± 0.028 
6.259 ± 0.088 
25.47 ± 0.02 
179.6 
0.307 ± 0.020 
19°C 
Low 
2.536 ± 0.029 
19.51 + 0.02 
196.3 
0.202 ± 0.028 
2.495 ± 0.020 
19.43 ± 0.02 
157.6 
0.214 ± 0.022 
High 
7.361 ± 0.060 
19.73 ± 0.06 
189.5 
0.228 ± 0.028 
7.273 ± 0.058 
19.67 ± 0.04 
249.2 
0.207 ± 0.020 
