2.5.2. Oxygen-specific consumption and ammonium excretion
Before beginning the experiments, the animals were maintained
in the respirometer with continuous water circulation for
at least 90 min to attenuate the handling stress. Then, the water
supply was suspended and the respirometer closed, so that the fish
would consume the oxygen present in the known water volume for
a period of 1 h. The respirometers were protected by a barrier to
isolate the animals from possible movement in the laboratory.
The respirometer was made in our laboratory, with tube of acrylic
and covers of PVC. The difference between the oxygen concentrations
determined at the beginning and end of the confinement
was used to calculate oxygen consumption. To minimize the effect
of low oxygen concentration and metabolite accumulation on the
metabolism, the experiment duration was regulated so that the
oxygen concentration at the end of experiments was at least 70%
of its initial concentration. The dissolved oxygen was determined
through the Winkler Method [27].
To obtain the desired concentration of Folidol 600, the necessary
volume of the substance (1 mg/Folidol 600/ml) was calculated
for each volume of respirometer and added with a
micropipette at the end of the acclimation period. As soon as the
substance was added, the entry orifice was immediately sealed.
After, the actual concentration of parathion was measured by
chemical methods. Additionally, the seawater in the respirometer
was sampled at the beginning and at the end of the oxygen consumption
analysis. Determination of ammonium–nitrogen in the
seawater was based on the phenolhypochlorite method [28]. The
average oxygen-specific consumption and ammonium excretion
by the fish was assessed using analysis of variance. All data were
analyzed using the Tukey’s multiple comparisons test (p < 0.05).
2.5.2. Oxygen-specific consumption and ammonium excretionBefore beginning the experiments, the animals were maintainedin the respirometer with continuous water circulation forat least 90 min to attenuate the handling stress. Then, the watersupply was suspended and the respirometer closed, so that the fishwould consume the oxygen present in the known water volume fora period of 1 h. The respirometers were protected by a barrier toisolate the animals from possible movement in the laboratory.The respirometer was made in our laboratory, with tube of acrylicand covers of PVC. The difference between the oxygen concentrationsdetermined at the beginning and end of the confinementwas used to calculate oxygen consumption. To minimize the effectof low oxygen concentration and metabolite accumulation on themetabolism, the experiment duration was regulated so that theoxygen concentration at the end of experiments was at least 70%of its initial concentration. The dissolved oxygen was determinedthrough the Winkler Method [27].To obtain the desired concentration of Folidol 600, the necessaryvolume of the substance (1 mg/Folidol 600/ml) was calculatedfor each volume of respirometer and added with amicropipette at the end of the acclimation period. As soon as thesubstance was added, the entry orifice was immediately sealed.After, the actual concentration of parathion was measured bychemical methods. Additionally, the seawater in the respirometerwas sampled at the beginning and at the end of the oxygen consumptionanalysis. Determination of ammonium–nitrogen in theseawater was based on the phenolhypochlorite method [28]. Theaverage oxygen-specific consumption and ammonium excretionby the fish was assessed using analysis of variance. All data wereanalyzed using the Tukey’s multiple comparisons test (p < 0.05).
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