溶氧水平对鲫鱼代谢模式的影响

Effect of dissolved oxygen level on metabolic mode in juvenile crucian carp

为了探讨水体溶氧水平对鲫幼鱼(Carassius carassius)运动、消化能力及其交互作用的影响,在(25.0±0.5)℃温度条件下,测定了8(饱和溶氧水平)、2和1mg/L溶氧水平下摄食(饱足摄食)和空腹组(空腹2 d)鲫鱼的临界游泳速度(Ucrit)、运动前耗氧率(MO2pre-exercise)、活跃耗氧率(MO2active)和代谢范围(MS)。摄食诱导的耗氧率上升在各溶氧水平下无显著差异。在饱和溶氧水平下,摄食组和空腹组的Ucrit没有显著差异,但在1和2 mg/L条件下,摄食组的Ucrit显著低于空腹组(P<0.05)。在饱和溶氧水平条件下,消化和运动诱导的耗氧率上升在各个游泳水平均能完全叠加,且摄食组鱼类与空腹组鱼类具有相似的MS和Ucrit和更高的MO2active,提示鲫鱼在常氧下为添加代谢模式。随着溶氧水平下降至2和1mg/L,呼吸能力(摄食组的MO2active)对溶氧水平下降较运动耗氧率更为敏感,消化诱导的耗氧率增加只能在较低游泳速度叠加,与空腹组鱼类比较,摄食组鱼类的MS和Ucrit显著下降,MO2active无显著差异,提示低氧下消化和运动对氧气需求竞争的加剧使其代谢模式转化为消化优先。

Under natural conditions, animals often need to carry out digestion and locomotion simultaneously. The physiological design of their cardio-respiratory systems must accommodate these simultaneous demands either by according emphasis to one of them or by somehow sharing them. The outcomes of the competition between digestion and locomotion i. e. , metabolic modes, are ecologically important in fish species. In this study, we selected crucian carp （Carassius carassius ）, one of the most hypoxia tolerant fish as experimental model and aimed to investigate the effect of water dissolved oxygen level on digestion, locomotion and their interaction in juvenile erueian carp. To achieve this goal, we measured the critical swimming speed （ Ucrit ）, pre-exercise oxygen consumption rate （MO2p ise ）, active oxygen consumption rate （ MO=activo） and metabolic scope （MS） of both fasting and fed fish at 8, 2 and 1 mg/L water dissolved oxygen level, under water temperature of （25.0±0.5） °C. The MO2p iso of fasting and fed fish （ satiate meal size） were 212.1 vs 488.3, 181.1 vs 418.2 and 106.4 vs 238.3 mg/kg, h, respectively, at 8, 2 and 1 mg/L. The Uo,t of fasting and fed fish were 5.83 vs 6.15, 5.17 vs 4.74 and 3.78 vs 3.08 BL/s, respectively, at 8, 2 and 1 mg/L. Digestion had no effect on U0rit at 8 mg/L, but it caused a significantly lower U rit in both 2 and 1 mg/L. The MO2active of fasting and fed fish were 689.9 vs 957.5, 587.5 vs 687.1 and 434.7 vs 469.9 mg/kg, h while the MS of fasting and fed fish were 463.2 vs 469.2,406.4 vs 268.8 and 328.3 vs 231.6 mg/kg, h, respectively, at 8, 2 and 1 mg/L. At 8 mg/L, the postprandial increase in restingMO2 was maintained at all levels of swimming speed till the highest swimming speed and fed fish showed a similar Ucrit, and MS but a significantly higher MO2active, which indicated that crucian carp exhibit the additive metabolic mode in normoxia. It suggest that the juvenile crucian carp can handle both digestion and aerobic locomotion simultaneously in normoxia due to the higher respiratory capacity and relatively lower metabolic capacity of digestive and locomotive tissues. Since the respiratory capacity （ as indicated by of fed fish） decrease more acutely than swimming capacity （ as indicated by and of fasting fish） with the decrease of dissolved oxygen level, the elevated MO2 due to digestion can be maintained under only lower swimming speed throughout the Ucrit test at both low dissolved oxygen level, but the fed fish end up having a profoundly lower Uc., and MS and a similar MO2ective compared with fasting fish, which indicate that crucian carp exhibit the digestion-priority metabolic mode in hypoxia due to the intensified oxygen demand competition between digestion and locomotion. The present study showed that the impairment of postprandial aerobic swimming performance increased with decreasing water dissolved oxygen level due to the unparalleled changes in the central cardio-respiratory, peripheral digestive and locomotory capacities of crucian carp. The different metabolic strategies of juvenile crucian carp at different water dissolved oxygen levels may relate to changes in oxygen demand and supply