2.2. Effects of hypoxia and feeding on bimodal respiration
Fish (N = 16, 65.2 ± 2.7 g, mean ± S.E.M.) were weighed and transferred to a respirometer in the afternoon and allowed to settle until the following day (20 h). The respirometer and the water surface were covered with black plastic to keep it dark and shielded from disturbance, in order to keep the fish as calm as possible. The experiment was conducted in a separate group of fish in normoxia (100% air satura- tion ~150 mm Hg) and hypoxia (20% air saturation ~30 mm Hg). 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 from water (MO2w) and air (MO2a) was measured to calculate standard metabolic rate (SMR) and partitioning. Hereafter fish were either force fed 5% of their body-mass as grounded fish fillet, or sham fed. During force-feeding, the fish were held out of water 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. None of the fish 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.
2.2. ผลของ hypoxia และอาหารบนหายใจ bimodalFish (N = 16, 65.2 ± 2.7 g, mean ± S.E.M.) were weighed and transferred to a respirometer in the afternoon and allowed to settle until the following day (20 h). The respirometer and the water surface were covered with black plastic to keep it dark and shielded from disturbance, in order to keep the fish as calm as possible. The experiment was conducted in a separate group of fish in normoxia (100% air satura- tion ~150 mm Hg) and hypoxia (20% air saturation ~30 mm Hg). 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 from water (MO2w) and air (MO2a) was measured to calculate standard metabolic rate (SMR) and partitioning. Hereafter fish were either force fed 5% of their body-mass as grounded fish fillet, or sham fed. During force-feeding, the fish were held out of water 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. None of the fish 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.
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