Tuesday, July 24, 2012

Monster in the Oxbow Lake

So I was watching a rerun of the Salad approved, River Monsters, last week. Jeremy Wade was after the Arapaima of the amazonian watershed. This fish is over fished to a large extent and Jeremy was on the quest for one of the increasingly rare giants of the species. As he usually does he conferred with the locals as to where the big ones hide out. He met luck in a small oxbow lake.

Now oxbow lakes are special little habitats and I was a little surprised to find that this obviously large predatory fish would often strand itself in little oxbow lakes when you might assume it would want to live in the main river channel with access to more abundant prey. I looked up Arapaima at wikipedia and learned:

The fish is an air-breather, using its labyrinth organ, which is rich in blood vessels and opens into the fish's mouth,[6] 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?


1 comment:

BK said...

I think the doubly efficient theropod breathing mechanism gave them a lethal edge over mammals when these two were the only ones that survived the T-J extinction.

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