| In this study, the aerial respiratory metabolism of the snakehead Channa argus was studied to determine the contributions of the supra-branchial organ accessorial breathing, the blood oxygen-carrying capacity, and the anaerobic metabolic capacity to aerial survival were determined. The fish was also treated by feeding, temperature, and exhaustive exercise to intensify the imbalance between oxygen supply and demand. Two experiments were conducted. In experiment I, aerial respiratory metabolic rate(MRAir), red blood cell count(RBCC), haemoglobin content(Hb), blood ammonia concentration(NH3-N), lactic acid content in liver(LDL) and white muscle(LDWM) were measured in the fish during aerial respiration at 25℃. In experiment II, MRAirs were measure in the fish fed with meals of 0%, 1%, and 3% body mass at 25℃, and in the fish treated by different temperatures(20, 25, and 30℃), and in the fish treated by exhaustive exercise at 25℃.The results were as follows:1. Resting aerial metabolic rate(RMRAir) was significantly lower than Resting metabolic rate in water(RMRWater) in both the control fish and the fish sheared supra-branchial organ, with declines of 22.4 and 23.5%, respectively. Both RMRAir and RMRWater did not significantly differ between the control fish and the sheared fish. The survival duration of the sheared fish was significantly shorter than that of the control fish. RBCC, Hb, and LDL of the fish in air were not markedly different to those of the fish in water. The NH3-N tended to increase during aerial respiration.2. There was no significant difference in MRAir as feeding level increases. In air, the dry matter digestion ratio of the fish fed at 1% and 3% were 57.6 and 30.3%, respectively. As temperature increased, RMRWater and RMRAir markedly increased, however, the survival duration significantly shortened. The peak MRWater post exhaustive exercise was significantly higher than RMRWater, but the peak MRAir was not significantly higher. The peak MRAir post exhaustive exercise was significantly lower than the peak MRWater, and both were higher than RMRAir.The conclusions suggested in this study were as follows:1. In the present study, RMRAir of the sheared fish did not differ to that of the control fish, which suggests that the supra-branchial organ of the snakehead contributes less to aerial respiration and may not be the only accessorial breathing organ of the snakehead. It indicates that there may be other accessorial breathing ways. The decline in the metabolic rate of the snakehead from water to air suggests metabolic depression to some extent.2. Both RBCC and Hb of the snakehead did not change during aerial respiration, suggesting that the blood oxygen-carrying capacity affects little on aerial survival ability. LDL of snakehead did not markedly vary during aerial respiration, but LDWM decreased at 1.5 and 12 h, which suggests that the anaerobic metabolic capacity does not enhance in the fish in air. NH3-N tended to increase during aerial respiration, which suggests that ammonia wastes may be accumulated in the body, resulting a short aerial survival period of the snakehead.3. The snakehead in air showed no significant feeding metabolic response and its survival duration shortened with increasing feeding rate, suggesting that the accessorial breathing ability of the snakehead can maintain only basic metabolic demands in air, rather than the extra demand of feeding metabolism. RMRAir increased with increasing temperature, but the survival duration shortened, which should be due to an increasing aerial breathing ability, but an aggravating imbalance between oxygen supply and demand. MRAir did not increase after exhaustive exercise, but was higher than RMRAir of the aerial control, suggesting that the metabolic ability of the snakehead in air can be enhance to some extent, as extra metabolic demands increase. |
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