The call of the not-so-mild.

Along with other nutrients, animals need trace metals to function. Iron, the oxygenbinding component in the blood pigment hemoglobin, is a critical trace metal and is usually absorbed through the gut. Mammals can alter iron metabolism in order to meet oxygen demand during periods of low environmental oxygen – hypoxia. However, it was unknown whether hagfish – a much more primitive group of animals that exhibit unusual tolerance to hypoxia – change their iron dynamics to achieve such resilience and whether they could take up iron from their environment. Knowing that hagfish can absorb some nutrients through their skin, Chris Glover, of Athabasca University, Canada, and colleagues from several other Canadian institutions set out to determine whether hagfish can take up iron across the skin; if so, how it might compare with gut uptake; and whether changes in iron transport during hypoxia contribute to the impressive hypoxia tolerance of these hardy fishes.