Wow, that's strange...
While we were diving the other day, we came across a most unusual fish. When I see things under the ice that I am not sure about, I simply have to ask around to find out more. I am so fortunate to be surrounded by such knowledgeable and amazing people. Everyone is willing to teach me so much.
Here's a little bit of what I learned about this unique find!
Antarctic Icefish (Pagetopsis macropterus)
Here in McMurdo, these fish are a little harder to find. Look carefully. Can you find the Icefish in this photo?
Meet Pagetopsis macropterus. A most unusual fish. (Photo courtesy of Adam Marsh)
Pagetopsis is unique because of a structure that it lacks. It belongs to a family a fish that have no hemoglobin. Hemoglobin is the part of red blood cells that carries oxygen - most vertebrates (organisms with backbones) have hemoglobin. Icefish are the only vertebrates that don't have hemoglobin as adults! Why? Yesterday, we were talking about Adaptations. So, that got me thinking: "Can a lack of something (like hemoglobin) be a useful adaptation?"
Well, as it turns out, not all scientists are convinced that this is a useful adaptation. The more and more I read about Pagetopsis, the more it seems that there is still a lot of work to be done on understanding the development of these hemoglobin-less fish. Here's a little bit about the two-sides of the interesting discussions that scientists are having about hemoglobin-less fish.
It Might Be an Adaptation
Scientists originally thought that a lack of hemoglobin might be an adaptation to living in the very cold seawater of Antarctica.
First, the icefish doesn't need to expend energy producing hemoglobin in the first place. This saves some energy in a part of the ocean where conserving energy is really helpful.
Second, it takes a lot of energy to push that hemoglobin around inside your body. So, to conserve energy the icefish uses a different system. It has adapted to absorb oxygen from the sea water around it. The oxygen is dissolved in the icefish's blood and pumped around their body.
So, the basic thought was that a lack of hemoglobin could be an adaptation to save the icefish some energy.
It Might Not be an Adaptation
As it turns out, after some more careful study, some of the consequences of not having hemoglobin means that fish like Pagetopsis have to use energy in other ways to compensate. For example, fish like Pagetopsis usually have to:
- Have larger amounts of blood in their bodies
- Have larger hearts to pump all that blood
- Have lower metabolism
All of these require more energy. So, it might be that being hemoglobin-less costs more energy than it saves.
Hmmm...
I think this is a great example of how scientists are always pushing the boundaries of what we know. These are difficult questions, but can help us to understand the role of hemoglobin in organisms, including humans.
You can learn a lot more about the Icefish from fellow PolarTREC teacher Paula Dell by clicking here.