African river prawn facts for kids

The Macrobrachium vollenhoveni, also known as the African river prawn, is a large and important type of prawn. It belongs to the Palaemonidae family and lives in West Africa. These prawns are special because they are catadromous. This means they move from fresh river water to slightly salty water (brackish water) to lay their eggs. After the eggs hatch, the baby prawns move back to freshwater to grow up. Scientists are also studying if these prawns can help control a disease called schistosomiasis in people.

Discover the African River Prawn

What Does It Look Like?

The African river prawn is quite big. It can grow up to 189 millimeters (about 7.4 inches) long. Most often, you'll find them between 100-150 millimeters (about 4-6 inches). They are usually a pale color. They don't have spots. Instead, they have a thin dark line along their back. They also have stripes across their body. The third pair of mouthparts, called maxillipeds, are bright yellow. The claws on their second pair of legs are dark blue. They have a yellow spot where the claw joins the leg.

Special Features of the Prawn

The prawn's "nose," called the rostrum, is about the same length as its antenna scale. The top edge of the rostrum is curved over its eye. The very tip of the rostrum has a short part with no teeth. On their second pair of legs, the part called the carpus is shorter than the palm of the claw. The movable part of the claw has one large tooth in the middle.

Where Do African River Prawns Live?

The African river prawn is found only in West Africa. You can see them from Senegal all the way to Angola. They also live on the islands of Bioko, São Tomé, and Cape Verde.

Life and Habits of the Prawn

Where They Live and How They Reproduce

African river prawns live in both fresh and brackish waters. This includes rivers and even mangrove creeks. They don't like very acidic water. After mating, the female prawns carry their eggs. They travel downstream from freshwater to areas where the river meets the sea. This is because the baby prawns need salty water to develop.

The eggs cannot hatch if the water is too salty. So, the females travel downstream during the rainy season. This is when the salty water in the river mouths becomes less salty. After hatching, the tiny baby prawns then move back upstream into the freshwater. There, they finish growing into adult prawns.

What Do African River Prawns Eat?

M. vollenhoveni prawns eat many different things. They are omnivores, meaning they eat both plants and animals. Most of their diet includes plant materials and tiny water plants called algae. They also eat very small living things like diatoms and protozoa. They are not picky eaters. They will eat plankton, especially green algae and diatoms. They are also known to eat dead plants and animals. They seem to prefer eating animal remains. People have even seen them eating tadpoles and small fish.

Prawns in Fishing and Farming

Catching African River Prawns

People catch African river prawns using traps made of leaves and brushes. They use these traps in both freshwater and brackish water. Often, people are trying to catch other types of prawns, like Macrobrachium felicinum or Macrobrachium macrobrachion. However, in places like Lagos Lagoon in Nigeria, some people fish for M. vollenhovenii full-time during peak season.

Farming African River Prawns

Many studies show that the African river prawn is great for farming. It is one of the largest prawns in its group. It can also live in many different environments. Plus, it eats many different things, which makes it easier to feed. The ways to farm these prawns are very similar to how people farm Macrobrachium rosenbergii, another popular prawn.

Scientists have also looked at how healthy these prawns are to eat. They even studied if the prawn shells, which are usually thrown away, could be used as food for other farmed animals. As of 2017, large-scale farming of M. vollenhovenii has not become common. This might be because people didn't fully understand that the eggs need saltier water to hatch.

Prawns Helping Fight Disease

How Prawns Can Control Schistosomiasis

The African river prawn is an omnivore. This means it eats both plants and animals. Larger prawns will eat freshwater snails. Some of these snails carry tiny parasitic flatworms called Schistosoma. These worms can infect humans and cause a disease called schistosomiasis. This disease is also known as bilharzia.

On the Senegal River, a dam called the Diama Dam was built. This dam blocked the prawns from reaching the salty water they needed to breed. Because of this, the prawn populations upstream of the dam disappeared. After the prawns were gone, there was a huge increase in schistosomiasis infections. In some villages, up to 71.8% of people got the disease. This showed that losing the prawns might have caused the disease to spread more.

Scientists knew that another type of prawn, M. rosenbergii, could eat these snails in labs. So, they thought M. vollenhovenii might do the same. They found that it did! Larger male prawns were better at eating the snails. So, scientists focused on raising only male prawns. These male prawns could then be put into rivers.

Benefits of Using Male Prawns

• Male prawns grow faster and larger.
• They don't tend to move downstream to lay eggs.
• They stay close to where they are put into the river.
• They can be guided into shallow water where the snails are found. This makes them even better at eating the snails.

Also, people can still catch and eat these prawns. The worms that cause schistosomiasis cannot be passed to humans by eating the prawns. Using prawns is a promising way to help control schistosomiasis. It can work along with medicines and other ways to control the disease, like using catfish and domestic ducks.