Anova-analysis showed significant differences (P < 0.05) in dissolved oxygen level between the system R and the system F; however, there were no significant differences (P > 0.05) between the two dietary treatments within the same system. Dissolved oxygen mostly remained between 6 and 7 mg·L− 1 in the low water exchange recirculation system (R) for both dietary treatments (6.54 ± 0.29 mg·L− 1 and 6.66 ± 0.44 mg·L− 1 respectively for the treatments RL and RC), while it fluctuated between 4 and 6 mg·L− 1 in the flow-through water system (F) for both dietary treatments (5.41 ± 0.76 mg·L− 1 and 5.40 ± 0.55 mg·L− 1 respectively for the treatments FL and FC) (Table 1). Anova-analysis showed no significant differences (P = 0.3528 > 0.05) for the pH among the treatments. Although the pH was very similar between the R and F rearing systems, ranging from 7.3 to 8.0, it was more stable in the R system than in the F system (Table 1, Fig. 2a). Alkalinity declined over time in both rearing systems, gradually decreasing from 100 mg·L− 1 at the beginning of the experiment to 60 mg·L− 1 at the end of the experiment. However, in the R system the decline was more rapid, with alkalinities remaining high between 80 and 100 mg·L− 1 during the first 4 weeks of the experiment, but then soon decreasing down to 70 and then 60 mg·L− 1 thereafter. In the F system, alkalinities remained high between 80 and 100 mg·L− 1 for the first 8 weeks of the experiment, before starting to decrease down to 70 mg·L− 1 later on (Table 2, Fig. 2b).
Anova-analysis showed significant differences (P < 0.05) in dissolved oxygen level between the system R and the system F; however, there were no significant differences (P > 0.05) between the two dietary treatments within the same system. Dissolved oxygen mostly remained between 6 and 7 mg·L− 1 in the low water exchange recirculation system (R) for both dietary treatments (6.54 ± 0.29 mg·L− 1 and 6.66 ± 0.44 mg·L− 1 respectively for the treatments RL and RC), while it fluctuated between 4 and 6 mg·L− 1 in the flow-through water system (F) for both dietary treatments (5.41 ± 0.76 mg·L− 1 and 5.40 ± 0.55 mg·L− 1 respectively for the treatments FL and FC) (Table 1). Anova-analysis showed no significant differences (P = 0.3528 > 0.05) for the pH among the treatments. Although the pH was very similar between the R and F rearing systems, ranging from 7.3 to 8.0, it was more stable in the R system than in the F system (Table 1, Fig. 2a). Alkalinity declined over time in both rearing systems, gradually decreasing from 100 mg·L− 1 at the beginning of the experiment to 60 mg·L− 1 at the end of the experiment. However, in the R system the decline was more rapid, with alkalinities remaining high between 80 and 100 mg·L− 1 during the first 4 weeks of the experiment, but then soon decreasing down to 70 and then 60 mg·L− 1 thereafter. In the F system, alkalinities remained high between 80 and 100 mg·L− 1 for the first 8 weeks of the experiment, before starting to decrease down to 70 mg·L− 1 later on (Table 2, Fig. 2b).
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