Hypoxic events have always naturally occurred in freshwater ecosystems but are worsening due to anthropogenic activities. Hypoxia tolerance greatly varies among fish species and is difficult to quantify in nature in large fish species. We analysed the movements of 40 subadult and adult European catfish Silurus glanis [(727; 2150) mm] exposed to a natural summer hypoxic event in a shallow lake of southeastern France. Catfish could withstand very low dissolved oxygen concentrations (DOC), down to 1.3 mg/L in the upper half of the water column (corresponding to a mean dissolved oxygen saturation rate of 16%), when their preferred benthic habitats were anoxic. While hypoxia was becoming more severe, individuals significantly increased their activity and the surface area they visited, whatever their size. This led them to a refuge zone where they aggregated or stayed in close vicinity, very little mobile, over one and a half day during the overall anoxia of the lake. This zone, located very close to the well oxygenated water inflow, was probably one of the most oxygenated accessible zone. However, during this aggregation, the smallest individuals were more active than the largest ones. This was probably because they more often needed to move to better-oxygenated places within the gathering area, compared to larger dominant fish that occupied the best places. The ability of catfish to withstand very low DOC, along with its high optimum temperature range, could give it a competitive advantage over other predatory species in the context of global change.

缺氧事件总是自然发生在淡水生态系统中，但由于人为活动而恶化。不同鱼类的缺氧耐受性差异很大，在自然界中大型鱼类很难量化。我们分析了 40 条亚成体和成体欧洲鲶鱼Silurus glanis的运动[(727; 2150) mm] 在法国东南部的一个浅湖中暴露于自然的夏季缺氧事件。当鲶鱼首选的底栖生境缺氧时，鲶鱼可以承受非常低的溶解氧浓度 (DOC)，在水柱的上半部分低至 1.3 mg/L（对应于平均溶解氧饱和率 16%）。虽然缺氧变得更加严重，但无论大小，个体都显着增加了他们的活动和他们访问的表面积。这将他们带到了一个避难区，在那里他们聚集或停留在附近，几乎没有移动，在湖的整体缺氧期间超过一天半。该区域非常靠近含氧水流入井，可能是含氧量最高的可及区域之一。然而，在这个聚合过程中，最小的个体比最大的个体更活跃。这可能是因为与占据最佳位置的大型优势鱼类相比，它们更经常需要移动到聚集区域内氧气含量更高的地方。在全球变化的背景下，鲶鱼能够承受非常低的 DOC 以及其较高的最佳温度范围，可以使其比其他捕食性物种具有竞争优势。