Antarctica is world’s 5th largest continent on our planet after Asia, Africa, North America and South America. It is surrounded by ocean from all sides. It has surface area approximately 14 million Km2.
Adverse climatic conditions have remarkable impact on fish, animal and plant life on Antarctica. World’s 70% fresh water is frozen in form of ice. Total ice on continent is 98% and 2% water. Sun shines every six months and other six months are in night. Maximum lowest temperature recorded on Antarctica is -89OC on land and water below ice is at around -2.5OC (freezing point of water is below 0OC low because of salts in water). Average thickness of ice layer on Antarctica is about 1.6Km.
In these distinct conditions fish life flourishes and expands. Ice fish and Antarctic Cod/Toothfish are among the species which can sustain in adverse conditions.
Antarctic Cod is also called Toothfish though they have no specific distinguishable similarities. Cods are found in Artic, Pacific and Atlantic oceans. Toothfish can be classified in two categories[1] as Patagonian Toothfish and Antarctic Toothfish. Patagonian Toothfish is found in warmer water conditions above Antarctic. Antarctic Toothfish are generally found 60O South in Ross Sea. Scientific classification[2] is as follows:
Kingdom | Animalia |
Phylum | Chordate |
Class | Actinopterygii |
Order | Perciformes |
Family | Nototheniidae |
Genus | Dissostichus |
Species | mawsoni |
Antarctic Cod is in 1.5 – 2 m in length and 120 – 150 Kg in weight in general. They grow 60cm per 5 years and reach to 1.5m in 20 years. 150 Kg Cod is recorded in literature. Scientist estimate they can live up to 50 years (±5 years). They can breed when they are in the range of 70cm to 90cm, at this length they are at the age between 8 to 10 years[3].
They have quality to change colour with change in depth of ocean. They can turn themselves in Grey-Green as well in Reddish-Brown as ocean becomes dipper. They have light weight cartilaginous skeleton[4] and no swim bladder, which helps them to swim faster and deeper. They are generally found in range of 300m to 2500m[5].
Tropical mammals and fishes have eye lenses which get frozen in varied climatic conditions of Antarctica. They have good eye sight in temperature range of 20OC to 7OC. But Toothfish have eye lenses[6] which can bare repeated cold conditions of -12OC with stable protein structure. They have developed retinas. It enables them to swim so dipper where sun rays cannot reach, especially in winter because of snow.
Question arises, ‘How they can survive in below freezing point temperature of water’. In general, there are few mechanisms. First, some species accumulate sodium, potassium or chlorine ions or urea[7] around their body to lower temperature. Second, some of them have extremely efficient enzyme system which keeps them as active at 0OC as that of fish at 20OC. Third, survival by using Glycoproteins. Glycoproteins are the proteins, present in the body of Toothfish. When temperature approaches freezing point crystallization of water starts. Billions of nuclei are formed. Secretion of Glycoproteins[8],[9] forms thin layer on the surface of nuclei and prevents crystallization. This occurs on the body surface.
As we know from Henry’s law, as temperature of water decreases, the equilibrium concentration of oxygen increases as shown below.
Their blood doesn’t contain hemoglobin and red blood cells. At these low temperatures, oxygen transport occurs by blood plasma. This makes their blood transparent and animal saves energy of pumping heavy blood. Since oxygen concentration is higher, it slows metabolism, resulting in conservation of energy.
They feed[10] on molluscs, crabs, starfish, worms, squids, prawns and small fish. They consume anything like remains of penguins caught by seals or orca on the surface. In research, it has been found that, Toothfish are very active and feed in summer because of 24 hrs of light, but they take rest in winter though plenty of food is available. They are the food of predators like sperm whale and elephant seal, generally.
Another important characteristic of Toothfish is that their heart beats every 6 seconds. This will boost research in cardiac medicine industry. Future application would be lowering heart beats of human while undergoing medical surgery.
These qualities of Toothfish have pulled them in risk of extinction. CCAMLR (Convention for the Conservation Antarctic Marine Life Resources) has limited fishing to precautionary catch level in Ross Sea.
[4] Fishes of the Southern Ocean. O Gon & PC Heemstra, eds. Grahamstown, South Africa : JLB Smith Institute of Ichthyology, 1990
