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].