The Amazing Icefish
Most vertebrates have red blood but the blood of the antarctic icefish, (Chaenocephalus aceratus) is clear (and actually looks a little like slush). This is because the blood of this incredible fish lacks red blood cells which carry an important pigment called haemoglobin.
What is haemoglobin?
Haemoglobin is a red pigment present inside red blood cells which has the ability to carry oxygen. It is responsible for the red colour of the blood of animals like mammals, birds, reptiles and fish.
The cells of most organisms rely on oxygen in order to produce the energy they need to survive.
In most vertebrates a small amount of oxygen is transferred through the blood in a physically dissolved form (that is, it is dissolved in the blood. A bit like how sugar is dissolved in coffee).
However most of these organisms rely heavily the oxygen carrying ability of their haemoglobin for the bulk of their oxygen transfer.
Why not just have dissolved oxygen?
The amount of oxygen that can be dissolved in the blood is far less(0.3% of blood volume) than what can be carried by the total amount of haemoglobin (20% of blood volume). If an organism were to rely on only dissolved oxygen, it would have to move its blood a lot faster through its body to deliver enough oxygen to the tissues on time to meet energy demands.
So what about the icefish?
The icefish has no haemoglobin in its blood and so relies completely the amount of oxygen it can dissolve into it’s blood to be delivered to tissues and meet energy demands.
To put things in perspective, when human’s haemoglobin is compromised, as is the case in carbon monoxide poisoning, they become very sick and may die.
The icefish, however, is perfectly fine. This is because, the it has an incredibly large heart which significantly increases the speed at which blood moves through its body as well as increased blood volume and large capillaries which allows it to deliver enough oxygen to its tissues on time to meet energy demands.
Because of these adaptation, the icefish is able to do what no other vertebrate has done. Survive with no haemoglobin.
Future of the Icefish
Climate change may prove especially difficult for the icefish. Since warmer waters can hold less oxygen than colder waters it is believed that the warming of its ocean home may lead to the water in which the fish lives to become too poor in oxygen for it to survive without haemoglobin.
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