The fish is an air-breather, using its labyrinth organ, which is rich in blood vessels and opens into the fish's mouth, an advantage in oxygen-deprived water that is often found in the Amazon River. This fish is therefore able to survive in oxbow lakes with dissolved oxygen as low as 0.5 ppm. In the wetlands of the Araguaia, one of the most important refuges for this species, it is the top predator in such lakes during the low water season, when the lakes are isolated from the rivers and oxygen levels drop, rendering its prey lethargic and vulnerable.
So the Arapaima actually uses a differential ability to respire in these habitats to its advantage... cool. And in this episode it was mentioned that this oxbow lake reconnects with the main channel every wet season. Now all this begs the question- Does the Arapaima instinctively seek out these habitats or does the fish learn over its life that in these microhabitats it has the advantage? And, taking it a bit further, where else do we see predators using respiratory factors to their advantage? Where might differential respiratory attributes have played a pivotal role in deep time?