Atlantic cod

The Atlantic cod is a big fish.

It lives in the cold ocean. It can be brown or green with spots. A silver stripe runs down its side. This stripe helps it feel shakes in the water.

These fish like to stay near the sea floor. They often swim in large groups. Small fish hide in rocks to stay safe. Big cod can live for 25 years. Many people catch them for food.

The Atlantic cod is a large fish found in cold oceans.

It can be brown or green with spots. A silver stripe runs along its side. This stripe is a lateral line. It helps the fish feel vibrations in the water.

Cod like to stay near the sea floor. These are called demersal fish. They often swim in large groups called shoals. In a shoal, larger fish act as scouts. They help lead the group to food.

Cod are apex predators. This means they are at the top of the food chain. They eat many things like squid and shrimp. Large cod mostly eat other fish. Small cod mostly eat tiny creatures called crustaceans.

Humans have fished for cod for a thousand years. In the 1990s, many cod stocks collapsed. This means there were very few fish left. This happened because of heavy fishing. When the big cod disappeared, it changed the whole ocean. This is called a trophic cascade.

In Europe, some cod have now come back.

The Atlantic cod is a famous fish found in many cold parts of the ocean.

It belongs to a group of fish called Gadidae. These fish are very important because humans eat them all over the world. You might see them sold as salt cod or even as dried stockfish. In the western Atlantic, they live north of North Carolina and around Greenland. In the eastern Atlantic, they live from the Bay of Biscay to the Arctic Ocean. They can live for up to 25 years in the wild.

Cod have a very interesting way of living and moving. They are demersal fish, which means they like to stay near the sea bottom. They often swim in large groups called shoals. In these groups, the larger fish act as scouts to lead the way.

These scouts help the group find food during long trips. Smaller fish stay in the shoal to help them find food more easily. Cod also change how they act based on the water temperature. They like to stay in deep, cold water during the day. At night, they move to shallower and warmer water to save energy.

As apex predators, cod play a huge role in their ocean homes. This means they are at the top of the food chain. They eat many different things like squid, mussels, and clams. Small cod mostly eat tiny creatures called crustaceans. Larger cod prefer to eat other fish like herring or mackerel.

Sometimes, adult cod even eat young cod. This is called cannibalism. Because they are top hunters, their presence helps keep other sea life in balance. If too many cod are taken away, it can cause a trophic cascade. This is a big change that affects many other species in the ocean.

People have fished for cod for over a thousand years. North European fishers even followed the cod across the ocean to North America. However, heavy fishing caused a big problem in the 1990s. Many cod populations collapsed, meaning more than 95% of them disappeared. The Canadian government had to ban fishing cod in 1992 to help.

While some areas are still at risk, things are changing. A study from 2013 showed that cod in Europe have rebounded. Because of this, they were relabelled as a species of "least concern" in that area.

Learning about cod helps us understand how the ocean works. Their bodies have special tools, like a stripe called a lateral line. This line helps them feel vibrations in the water. They also have a way of making new life through spawning. A female cod can release between 200,000 and 15 million eggs at one time. These eggs float in the water and drift with the currents. This movement helps carry the tiny babies to safe places to grow. Watching how cod react to light and temperature shows us how living things adapt to stay alive.

The Atlantic cod, known scientifically as *Gadus morhua*, is a vital marine fish belonging to the family Gadidae. It is a widely consumed species that plays a major role in both ocean ecosystems and human economies. Found in the cold waters of the North Atlantic, these fish inhabit areas ranging from the coastal shoreline down to the continental shelf. In the western Atlantic, they live north of Cape Hatteras, North Carolina, and around Greenland and the Labrador Sea. In the eastern Atlantic, their range extends from the Bay of Biscay to the Arctic Ocean.

Atlantic cod are demersal fish, meaning they prefer living near the sea bottom on coarse sediments. They are also shoaling species, which means they move in large, organized groups called aggregations. Within these shoals, fish are often organized by size. Larger fish act as scouts to lead the group during migrations. These scouts consume a higher and more variable quantity of food. Meanwhile, smaller fish trail behind and benefit from social facilitation. This social behavior helps the smaller fish find food more successfully than if they swam alone.

As apex predators, Atlantic cod sit at the top of many marine food webs. Their diet changes as they grow. Small cod primarily eat crustaceans, such as shrimp or crabs. As they become larger, they transition to eating more fish, including herring, mackerel, and sand eels. They also consume squid, mussels, clams, and sea cucumbers. In some regions, they even practice cannibalism. Studies show that in the northern North Sea, cannibalism can account for as much as 10% of their diet. Some reports suggest it can be as high as 56%.

To survive, cod must carefully manage their energy through homeostasis. This is the process of maintaining a stable internal environment. They are highly sensitive to water temperature. A change of only a few degrees can cause a massive increase in metabolic rate. For example, a small temperature decrease can raise metabolic costs by 15% to 30%. To save energy, cod adjust their depth based on the time of day. They typically stay in deeper, colder water during the day. At night, they move to shallower, warmer layers.

Reproduction for the Atlantic cod involves complex social behaviors and massive numbers of offspring. Most populations spawn between January and May. They use a mating system similar to lekking, where males gather to establish dominance hierarchies. Females may choose a partner based on his status or sexual characteristics, such as sound production. Cod are batch spawners, meaning a female releases eggs in several groups. A single female can release between 200,000 and 15 million eggs. These eggs and the newly hatched larvae float freely, drifting with ocean currents to reach nursery areas.

Human history is deeply connected to the cod. For over a thousand years, North European fishers followed cod across the Atlantic to North America. However, modern fishing technology led to a massive increase in catches during the 1950s. This heavy pressure caused several stocks to collapse in the 1990s. In Canada, the biomass of cod declined by more than 95% of its historical maximum. This led the Canadian government to implement a fishing ban in 1992.

The loss of cod had serious consequences for the entire ocean. Because cod are apex predators, their removal caused a trophic cascade. This is a chain reaction where removing a top predator changes the entire ecosystem. Without cod to hunt them, populations of species like American lobsters, crabs, and shrimp increased significantly. This change in the food web serves as evidence of the cod's original role as a major predator.

Today, the status of Atlantic cod varies by region. In 1996, the IUCN Red List labeled the species as vulnerable. However, a 2013 assessment showed that European cod populations have rebounded. Consequently, they were relabelled as "least concern" in Europe. Despite this recovery, many other stocks remain at risk. Global fishing continues to be monitored by organizations like ICES and NAFO to manage these populations.