2.2. Respiratory responses to hypoxia
Respiratory frequency ( fR—breaths.min1) was measured
from the buccal pressure variations. Fish were
previously anesthetized by immersion into benzocaine
solution (0.1 g L1) after which a polyethylene catheter
(PE 60) was inserted through a small hole drilled in the roof
of the mouth and fixed with the help of a specially shaped
flange. After surgery, fish were transferred to a flow-through
respirometer, which was left in a larger experimental tank
supplied with aerated water at 28T1 -C where they were
kept for a recovery period of 12 h prior to experimentation.
To measure the buccal pressure variations, the PE catheter
was connected to a Narco P-1000B pressure transducer
coupled to the universal amplifier of a Narco Narcotrace 40
(Narco Bio-Systems, Houston, TX, USA) physiograph. The
catheter was also used to collect water samples from the
buccal cavity and measure the O2 tension of the inspired
water (PiO2).