Antarctic fishes

Some fish live in very cold water.

They have a special trick to stay safe. They make a kind of antifreeze in their blood. This stops them from freezing in the ice.

Some fish even have clear blood. They do not have the red parts that most fish use. This helps them live in the cold sea.

Many of these fish live on the seafloor. They have round fins to help them move. They use these fins to swim or crawl.

Some fish can grow very large. They can be two meters long. They live in the deep, dark ocean.

Many fish live in the freezing Southern Ocean. These fish have found special ways to survive the cold.

One group is called the icefish. Some icefish have colorless blood. They lack hemoglobin, which is a protein that carries oxygen. Most fish have red blood because of this protein. Icefish survive without it by having a larger heart. They also have more blood to move oxygen around.

Other fish use antifreeze glycoproteins to stay safe. These are special proteins that act like antifreeze. They bind to tiny ice crystals in the body. This stops the ice from growing and freezing the fish. The fish make these in the pancreas. They then send them into the gut or the blood.

Many of these fish live on the seafloor. They have rounded fins to help them move. Some species, like the Antarctic toothfish, grow very large. They can reach two meters in length. These big fish can live for many years. They live in deep water to find food like squid.

Many special fish live in the freezing Southern Ocean. These fish have found amazing ways to survive in the cold.

Some belong to a group called the icefish. These fish are famous because they have colorless blood. They lack hemoglobin, which is a protein that carries oxygen. Most fish have red blood because of this protein. Icefish survive without it by having a bigger heart. They also have a higher blood volume to move oxygen.

Other fish use something called antifreeze glycoproteins to stay safe. These are special proteins that act like antifreeze in a car. They bind to tiny ice crystals that enter the body. This stops the ice from growing and freezing the fish inside. The fish make these proteins in the pancreas. They release them into the digestive tract to wrap around ice. The fish can then safely get rid of the ice. Unused proteins go to the liver to be stored.

Scientists study these fish to learn about adaptive radiation. This is a process where many different species grow from one ancestor. This happens when they move into empty spaces in nature. These fish grew to fill many different roles in the ocean. Some live on the seafloor, while others swim in the open water. They have changed their bodies to fit these different homes. This helps them live together in the same area.

These fish have many different shapes and sizes. The Channichthyids are the largest fish in this group. They can grow to a maximum of 40 centimeters. The Harpagifer is the smallest at only 1.5 centimeters. Some fish, like the Antarctic toothfish, are even bigger. They can grow up to two meters long. These large fish can live for many decades. They live in deep water from 100 to 3,000 meters.

Most of these fish spend their lives on the seafloor. They have rounded fins to help them move well. Their eyes are on top of their heads. This helps them see prey as they move up from the bottom. Many species also guard their eggs to keep them safe. They might attach eggs to rocks or sponges. The eggs take about five months to hatch. This long time is because the water is so cold.

The Southern Ocean is home to a highly specialized group of fish. These animals are adapted to survive in extreme cold. They are often referred to as Antarctic fishes. This group includes many different families of species. The most species-rich family is the Liparidae, also known as snailfishes. Another major group is the Nototheniidae, which are called cod icefishes. These fishes belong to a larger suborder called Notothenioidei. They are famous among scientists for their unique biological adaptations. These traits allow them to thrive where most other fish would freeze.

One of the most incredible adaptations involves antifreeze glycoproteins, or AFGPs. These are special proteins that prevent the fish from freezing internally. The fish produce these AFGPs in their pancreas. They are then released into the digestive tract. There, the proteins wrap around tiny ice crystals that enter the body through food or water. This binding prevents the ice from growing larger. The fish then safely excrete the crystals with their waste. Any unused AFGPs are recycled back to the liver for storage. Fish also use these proteins in their mucus and skin to prevent external freezing.

Some species have even more radical changes to their bodies. The Channichthyids, or icefish, are famous for having colorless blood. They lack erythrocytes, which are the red blood cells found in most animals. These fish also lack hemoglobin, the protein that typically binds to oxygen. Because they do not use hemoglobin, their blood lacks color. To survive without it, they have developed several compensations. They possess a higher blood volume and improved heart output. They also have a higher uptake of oxygen and lower metabolic rates. This allows them to transport oxygen through their bodies effectively.

These fishes show amazing variety in their physical forms. Most have rounded pectoral and pelvic fins to help them move. Many are benthic, meaning they live on the seafloor. However, some have moved into the water column through a process called pelagization. They achieved this by decreasing minerals in their skeletons. They also increased the amount of lipids, or fats, in their bodies. This makes them neutrally buoyant, so they do not sink. This adaptation reduces the energy they need to stay afloat. Their eyes are often set towards the top of their heads to spot prey.

The size of these fish varies greatly across different species. The Channichthyids can reach a maximum size of 40 centimeters. In contrast, the Harpagifer is very small, measuring only 1.5 centimeters. Some species are much larger, like the Antarctic toothfish. These can grow up to two meters in length. They can live for many decades in the deep ocean. They inhabit depths ranging from 100 meters to 3,000 meters. These large fish feed on squid, other fish, and benthic crustaceans.

Scientists use these fishes to study adaptive radiation. This is the process where many species develop from one common ancestor. This happens when species move into new, empty ecological niches. The history of these fish is tied to the movement of continents. About 122 million years ago, Antarctica separated from South America. This separation created the Drake Passage and the Antarctic Circumpolar Current. The resulting cooling caused a mass extinction of many local organisms. This left many empty niches for the Notothenioids to colonize. This event triggered their rapid diversification.

The life cycles of these fish are also shaped by the cold. Notothenioids generally live for about ten years. They often reach sexual maturity between three and four years of age. Spawning usually happens in the summer or fall. Many species are known to be excellent parents. They will nest and guard their eggs to protect them from predators. They may also move eggs to improve oxygen levels. Because the water is so cold, the eggs have a long incubation period. It can take around five months for the eggs to hatch. Once they hatch, the larvae have well-developed bodies to help them swim and survive.