Rates of hypoxia induction alter mechanisms of O2 uptake and the critical O2 tension of goldfish

The rate of hypoxia induction (RHI) is an important but overlooked dimension of environmental hypoxia that may affect an organism’s survival. We hypothesized that, compared with rapid RHI, gradual RHI will afford an organism more time to alter plastic phenotypes associated with O2 uptake and subsequently reduce the critical O2 tension (Pcrit) of O2 uptake rate (ṀO2). We investigated this by determining Pcrit values for goldfish exposed to short (∼24 min), typical (∼84 min) and long (∼480 min) duration Pcrit trials to represent different RHIs. Consistent with our predictions, long duration Pcrit trials yielded significantly lower Pcrit values (1.0-1.4 kPa) than short and typical duration trials, which did not differ (2.6±0.3 and 2.5±0.2 kPa, respectively). Parallel experiments revealed these time-related shifts in Pcrit were associated with changes in aspects of the O2 transport cascade: gill surface areas and haemoglobin-O2 binding affinities were significantly higher in fish exposed to...低氧诱导率（RHI）是环境低氧的一项重要却常被忽视的维度，其可能会影响生物体的存活。我们提出假说：相较于快速低氧诱导率，渐进式低氧诱导率将为生物体提供更多时间，以调整与氧摄取相关的表型可塑性，进而降低摄氧速率（ṀO2）的临界氧分压（Pcrit）。为验证该假说，我们通过测定金鱼在短时长（约24分钟）、常规时长（约84分钟）与长时长（约480分钟）的临界氧分压测试中的Pcrit值，以表征不同的低氧诱导率水平。结果与我们的预测一致：长时长临界氧分压测试得到的Pcrit值（1.0~1.4 kPa）显著低于短时长与常规时长测试的结果，后两者的Pcrit值分别为2.6±0.3 kPa与2.5±0.2 kPa，且二者无显著差异。平行实验显示，临界氧分压的这类时长相关变化与氧转运级联反应的多项参数改变相关：暴露于……的金鱼的鳃表面积与血红蛋白-氧结合亲和力均显著升高。