Astacus astacus

The noble crayfish lives in clean water.

It stays in rivers and lakes. It likes to hide in holes during the day. At night, it comes out to eat. It eats worms and small bugs. It also eats plants.

Many animals like to eat the crayfish too. Some animals can even eat their own kind. These crayfish are very important to the water. They help keep the water healthy. It is fun to learn about them!

The noble crayfish lives in fresh water.

You can find them in rivers and lakes. They live in many parts of Europe. This includes France and Finland. They like water with sand on the bottom. They stay in burrows during the day. At night, they come out to find food. They eat worms, insects, and plants.

These crayfish are very important. They are a keystone species. This means they help keep their home healthy. They eat plants to help the water stay good. Many animals eat them. Eels, otters, and minks are some of these predators.

People have eaten these crayfish for a long time. In the past, they were popular in Sweden. Some people even have them on their coats of arms.

Now, these crayfish face a big problem. A new kind of crayfish brings a disease. This is called the crayfish plague. Because of this, there are fewer noble crayfish today. They are now a vulnerable species. This means they are at risk of disappearing.

The noble crayfish is a special animal. It lives in fresh water like rivers and lakes. You might also call it the European crayfish. It is a very common species in Europe. These animals need clean water to live well. They stay in places that are not polluted. They can be found in many lands. This includes France and the Balkan Peninsula. They live as far north as Finland and Scandinavia.

These crayfish have a busy way of living. They are nocturnal, which means they are active at night. During the day, they rest in a burrow. They like to hide in places with lots of shelter. They prefer water with sand on the bottom. They do not like muddy water. To eat, they find worms and aquatic insects. They also eat molluscs and plants. This helps them stay healthy and strong. They help the water stay clean by eating plants.

Scientists have learned many things about them. In the 1990s, experts found special digestive enzymes. They call these enzymes astacins. These were first found in the noble crayfish. Now, we know these enzymes exist in many animals. They have even been found in humans. This shows how much we can learn from nature. Small discoveries can lead to big ideas about life.

People have a long history with this crayfish. In the Middle Ages, people in Sweden ate them. They were popular with the nobility back then. By the 1700s, all social classes ate them.

In northern Moldavia, people grew them in lakes. This was for special times in the Orthodox Christian calendar. A crayfish even appears on the coat of arms for Dorohoi County. They are a big part of Nordic culture today.

Today, the noble crayfish faces a hard job. A new species called the signal crayfish arrived. This new crayfish carries a disease called the crayfish plague. Because of this, the noble crayfish is now a vulnerable species. This means they are at risk. Their population has dropped to about 5% of what it was.

They are a keystone species in their homes. If they disappear, the whole water environment can change.

The noble crayfish, known scientifically as *Astacus astacus*, is a vital freshwater crustacean. It is also called the European crayfish or the broad-fingered crayfish. This species is the most common type of crayfish found across Europe. It plays a critical role in the health of the ecosystems it inhabits. Because it is a keystone species, its presence affects many other living things. If the noble crayfish disappears, the entire freshwater environment can change significantly.

These crayfish live strictly in fresh water environments. They require unpolluted streams, rivers, and lakes to survive. They prefer habitats with soft bottoms that contain some sand. However, they generally avoid areas with muddy water. To stay safe, they are nocturnal animals. This means they are active during the night and rest in burrows during the day. They also seek out habitats that provide plenty of available shelter.

The life cycle of *Astacus astacus* involves specific stages of growth and reproduction. They reach sexual maturity after three to four years and a series of moults. Breeding typically occurs during the months of October and November. Once the eggs are fertilized, the female carries them on her pleopods. These are specialized appendages used for carrying the eggs. The eggs remain attached to her until they hatch the following May. After hatching, the young crayfish begin to disperse into the water.

As part of the freshwater food web, the noble crayfish has a complex diet. They feed on worms, aquatic insects, and molluscs. They also consume various types of aquatic plants. This foraging helps boost primary productivity in their environment. However, they face many natural predators. These include the European mink, Eurasian otters, and muskrats. Fish like perch and pike also hunt them. Even other crayfish may engage in cannibalism.

Historically, the noble crayfish has been a significant food source for humans. Documentation of its consumption dates back to the Middle Ages. In Sweden, they were once a popular food for the nobility. By the 17th and 18th centuries, they were available to all social classes. In northern Moldavia, hundreds of small or large lakes were used to grow them. This was done to provide food during fasting periods in the Orthodox Christian calendar. This history is even reflected in the coat of arms of Dorohoi County.

Today, the species faces a very serious threat from an invasive species. The North American signal crayfish (*Pacifastacus leniusculus*) has been introduced to Europe. This invasive species carries a disease known as the crayfish plague. Because of this plague, the noble crayfish population has dropped to about 5% of its original size. Consequently, the IUCN Red List now classifies the species as vulnerable. This decline can lead to eutrophication, which is an increase in nutrients that lowers oxygen levels.

Scientific research has also uncovered unique biological details about this species. In the 1990s, researchers discovered a family of digestive enzymes called astacins. These enzymes were first isolated from *Astacus astacus*. Since that discovery, scientists have identified more than 20 different enzymes in this group. These astacins have been found in many different animals. These range from simple organisms like Hydra to complex animals like humans. This connection shows how deeply these biological tools are rooted in life.