The
hypoxic level was reached by manually adjusting the flow rate of N2
gas bubbled into the water. The respirometer (2.3 L) was contained in
a holding tank with 30 L of water. During this time the oxygen consumption
fromwater (MO2w) andair (MO2a)wasmeasured to calculate
standard metabolic rate (SMR) and partitioning. Hereafter fish were either
force fed 5% of their body-mass as grounded fish fillet, or shamfed.
During force-feeding, the fishwere held out ofwater and food placed in
the stomach by inserting a plastic tube (6 mm outer, 4 mm inner
diameter) through the mouth. The fish were not anaesthetised during
the sham or force-feeding procedure, which normally lasted less than
2 min.Noneof thefish regurgitated the food. The sham-feeding consisted
of inserting the tube into the stomach of the fish, without injecting feed.
After feeding, the fish were immediately returned to the respirometer
and measurements of MO2 resumed for another 20 h (sham-fed) or
23.5 (force-fed). The times were chosen after measuring in the first two
fish in each group, where MO2 had returned to SMR within these times.
Hereafter, the fish that had been force-fed were now sham-fed, and vice
versa, so that the effect of sham-feeding and force-feeding could be
compared within each individual, and furthermore to alleviate a possible
effect of time spent in the respirometer.