Laboratory of Evolutionary Physiology and Behavior, Chongqing Key Laboratory of Animal Biology, Chongqing Normal University, Chongqing, 400047, China.
Comp Biochem Physiol A Mol Integr Physiol. 2013 Jun;165(2):131-8. doi: 10.1016/j.cbpa.2013.02.028. Epub 2013 Mar 6.
To investigate the effects of diel-cycling hypoxia acclimation on the hypoxia tolerance, swimming and growth performance of juvenile southern catfish, we initially measured the critical oxygen tension (P(crit)), oxygen thresholds of aquatic surface respiration (ASR) and loss of equilibrium (LOE) of diel-cycling hypoxia-acclimated (15 d, 7:00-21:00, dissolved oxygen level (DO) = 7.0 ± 0.2 mg L(-1); 21:00-7:00, DO = 3.0 ± 0.2 mg L(-1)) and non-acclimated (15 d, DO = 7.0 ± 0.2 mg L(-1)) southern catfish at 25 °C. We then measured the critical swimming speed (U(crit)) and metabolic rate (MR) of hypoxia-acclimated and non-acclimated fish (under both hypoxic and normoxic conditions). The feeding rate (FR), feeding efficiency (FE) and specific growth rate (SGR) of fish in hypoxia-acclimated and non-acclimated groups were also measured. The P(crit), ASR and LOE of hypoxia-acclimated fish were significantly lower than those of non-acclimated fish. Hypoxia acclimation resulted in a significantly higher U(crit) when the individuals swam in hypoxia. The U(crit), maximum metabolic rate (MMR) and metabolic scope (MS) of both the hypoxia-acclimated and non-acclimated fish all decreased with the decrease of DO. However, the U(crit), MMR and MS decreased by 31, 43 and 54%, respectively, in non-acclimated fish, whereas these values decreased by 15, 28 and 29%, respectively, in hypoxia-acclimated fish, which suggests that hypoxia-acclimated fish were less sensitive to the DO decrease. The FR, FE and SGR all decreased by 21, 20 and 45%, respectively, in the hypoxia-acclimated group compared to the non-acclimated group. This result suggests that diel-cycling hypoxia acclimation improved the hypoxia tolerance and aerobic swimming performance of southern catfish, whereas impaired the growth performance. The high hypoxia tolerance and physiological plasticity to hypoxia-acclimated southern catfish may be related to its lower maintenance energy expenditure, sit-and-wait lifestyle and bottom-dwelling living environment condition (usually facing oxygen fluctuation). The growth performance of so-called 'visceral type' fish species, such as southern catfish, are more sensitive to hypoxia compared to other fish species because of their high peak post-prandial metabolic rate, which may be restrained by the limited aerobic metabolic scope in hypoxia.
为了研究昼夜循环低氧驯化对南方鲶幼鱼耐低氧能力、游泳和生长性能的影响，我们首先测量了昼夜循环低氧驯化（15 天，7:00-21:00，溶解氧水平（DO）=7.0±0.2mg/L；21:00-7:00，DO=3.0±0.2mg/L）和非驯化（15 天，DO=7.0±0.2mg/L）南方鲶的临界氧张力（P(crit)）、水面呼吸的氧阈值（ASR）和失衡点（LOE），温度为 25°C。然后，我们测量了低氧驯化和非驯化鱼（在缺氧和常氧条件下）的临界游泳速度（U(crit)）和代谢率（MR）。还测量了低氧驯化和非驯化组鱼的摄食率（FR）、摄食效率（FE）和特定生长率（SGR）。低氧驯化组鱼的 P(crit)、ASR 和 LOE 显著低于非驯化组鱼。当个体在低氧中游泳时，低氧驯化导致 U(crit)显著升高。低氧驯化和非驯化鱼的 U(crit)、最大代谢率（MMR）和代谢范围（MS）均随 DO 的降低而降低。然而，非驯化鱼的 U(crit)、MMR 和 MS 分别下降了 31%、43%和 54%，而低氧驯化鱼的 U(crit)、MMR 和 MS 分别下降了 15%、28%和 29%，这表明低氧驯化鱼对 DO 的降低不那么敏感。与非驯化组相比，低氧驯化组的 FR、FE 和 SGR 分别下降了 21%、20%和 45%。这一结果表明，昼夜循环低氧驯化提高了南方鲶的耐低氧能力和有氧游泳性能，但却损害了生长性能。低氧驯化的南方鲶具有较高的耐低氧能力和对低氧的生理可塑性，这可能与其较低的维持能量消耗、等待捕食的生活方式和底栖生活环境条件（通常面临氧气波动）有关。与其他鱼类相比，所谓的“内脏型”鱼类（如南方鲶）的生长性能对低氧更为敏感，因为它们的餐后高峰代谢率较高，这可能受到低氧中有限的有氧代谢范围的限制。
