Icefish - DS

Icefish, more commonly known as Antarctic Icefish, are a group of fish from the suborder notothenioids. They live in the Southern Ocean, surrounding the Antarctic, at temperatures ranging from 1.5 °C to -1.8 °C. Adapted to cold environments: they are extremophiles, more specifically cyrophiles ('cold-liking' organisms).

Antarctic Icefish are known for having a low metabolic rate and inactive lifestyle. They were first discovered in 1928 by a biologist named Ditlef Rustad, who noted their pale, translucent nature. Soon they were confirmed to be the only vertebrates that lack erythrocytes and haemoglobin. These organisms can weigh over 2kg and reach a length of approximately 0.6m. As they are ectotherms (with body temperatures equal to the surrounding waters), they have several adaptations to assist them with survival.

Behavioural Adaptations

 * Icefish use drag-based labriform swimming, which is slow and effortless. Therefore icefish can easily swim deeper into the water if they are too hot and closer to the water surface if they are too cold.

Anatomical Adaptations

 * At colder temperatures water is more absorbent to oxygen. Icefish use their cold surrounding to ensure they always have a plentiful supply of oxygen in their bloodstream.
 * The icefishes increased affinity to oxygen because of the cold enable them to have less haemoglobin. Less haemoglobin thins the blood, increasing its viscosity, so less energy is needed for the icefish to pump blood.
 * Icefish have a dense network of capillaries, large stroke volume and large blood vessels to ensure the maximum amount of blood is pumped around their body. This is especially important if the temperature of the surroundings drops too much, as the blood circulation can ensure thermoregualtion of the cells.

Physiological Adaptations

 * Icefish have watery muscles, so they are more buoyant. This makes it easier for them to swim at varying depths (i.e. if they are too cold they can quickly swim to the water surface).
 * Countercurrent heat exchange is used by icefish in their gills. This form of heat exchange enables the cold water going into the body to be heated by the warm water leaving the body, so the icefish will always have a lukewarm water supply within themselves.
 * Icefish utilise antifreeze glycoproteins which intercepts the bad effects of exteremly low temperatures. The antifreeze proteins prevent ice crystals from forming in their blood when the ocean temperatures fall below the freezing point of fresh water. Icefish swallow the freezing water and when swimming near the water surface are likely to hit the ice; without antifreeze catastrophic freezing would occur.