Laboratório Marítimo da Guia, Centro de Oceanografia, Faculdade de Ciências da Universidade de Lisboa, Av. Nossa Senhora do Cabo, 939, 2750-374 Cascais, Portugal.
J Exp Biol. 2013 Feb 1;216(Pt 3):359-68. doi: 10.1242/jeb.072587. Epub 2012 Sep 20.
The Humboldt (jumbo) squid, Dosidicus gigas, is a part-time resident of the permanent oxygen minimum zone (OMZ) in the Eastern Tropical Pacific and, thereby, it encounters oxygen levels below its critical oxygen partial pressure. To better understand the ventilatory mechanisms that accompany the process of metabolic suppression in these top oceanic predators, we exposed juvenile D. gigas to the oxygen levels found in the OMZ (1% O(2), 1 kPa, 10 °C) and measured metabolic rate, activity cycling patterns, swimming mode, escape jet (burst) frequency, mantle contraction frequency and strength, stroke volume and oxygen extraction efficiency. In normoxia, metabolic rate varied between 14 and 29 μmol O(2) g(-1) wet mass h(-1), depending on the level of activity. The mantle contraction frequency and strength were linearly correlated and increased significantly with activity level. Additionally, an increase in stroke volume and ventilatory volume per minute was observed, followed by a mantle hyperinflation process during high activity periods. Squid metabolic rate dropped more than 75% during exposure to hypoxia. Maximum metabolic rate was not achieved under such conditions and the metabolic scope was significantly decreased. Hypoxia changed the relationship between mantle contraction strength and frequency from linear to polynomial with increasing activity, indicating that, under hypoxic conditions, the jumbo squid primarily increases the strength of mantle contraction and does not regulate its frequency. Under hypoxia, jumbo squid also showed a larger inflation period (reduced contraction frequency) and decreased relaxed mantle diameter (shortened diffusion pathway), which optimize oxygen extraction efficiency (up to 82%/34%, without/with consideration of 60% potential skin respiration). Additionally, they breathe 'deeply', with more powerful contractions and enhanced stroke volume. This deep-breathing behavior allows them to display a stable ventilatory volume per minute, and explains the maintenance of the squid's cycling activity under such O(2) conditions. During hypoxia, the respiratory cycles were shorter in length but increased in frequency. This was accompanied by an increase in the number of escape jets during active periods and a faster switch between swimming modes. In late hypoxia (onset ~170 ± 10 min), all the ventilatory processes were significantly reduced and followed by a lethargic state, a behavior that seems closely associated with the process of metabolic suppression and enables the squid to extend its residence time in the OMZ.
洪堡巨鱿（巨型太平洋鱿鱼）是东热带太平洋永久性缺氧区（OMZ）的季节性居民，因此，它会遇到低于其临界氧分压的氧气水平。为了更好地了解这些海洋顶级捕食者在代谢抑制过程中伴随的呼吸机制，我们将幼年洪堡巨鱿暴露在 OMZ 中发现的氧气水平下（1% O(2)，1 kPa，10°C），并测量了代谢率、活动循环模式、游泳模式、逃逸射流（爆发）频率、套膜收缩频率和强度、冲程体积和氧气提取效率。在常氧条件下，代谢率在 14 到 29 μmol O(2) g(-1)湿质量 h(-1) 之间变化，具体取决于活动水平。套膜收缩频率和强度呈线性相关，随着活动水平的增加而显著增加。此外，观察到每分钟的冲程体积和通气量增加，随后在高活动期出现套膜过度膨胀过程。在缺氧暴露期间，鱿鱼的代谢率下降了 75%以上。在这种情况下，最大代谢率无法达到，代谢范围显著减小。缺氧改变了套膜收缩强度和频率之间的关系，从线性变为多项式，随着活动的增加而增加，这表明在缺氧条件下，巨型鱿鱼主要增加套膜收缩的强度，而不调节其频率。在缺氧条件下，巨型鱿鱼还显示出更长的膨胀期（收缩频率降低）和减小的放松套膜直径（缩短扩散途径），这优化了氧气提取效率（高达 82%/34%，不考虑/考虑 60%的潜在皮肤呼吸）。此外，它们进行“深呼吸”，具有更强的收缩力和增强的冲程体积。这种深呼吸行为使它们能够显示出稳定的每分钟通气量，并解释了在这种 O(2)条件下鱿鱼保持循环活动的原因。在缺氧期间，呼吸周期的长度缩短，但频率增加。这伴随着活跃期逃逸射流次数的增加和游泳模式之间更快的切换。在缺氧后期（开始~170±10 分钟），所有通气过程都显著减少，并随后进入昏睡状态，这种行为似乎与代谢抑制过程密切相关，并使鱿鱼能够延长其在 OMZ 的停留时间。
