Gymnarchus

The Gymnarchus niloticus, also known as the aba, aba aba, or frankfish, is a special kind of electric fish that lives at the bottom of rivers and lakes. It is the only species in its genus Gymnarchus and its family Gymnarchidae, which belongs to the order Osteoglossiformes. This fish has a long, slim body with no pelvic or anal fins, but it does have a tail fin that looks like a rat’s tail.

One of the most interesting things about the aba is how it moves and hunts. Instead of using its eyes to see, it swims using its long dorsal fin to stay straight, which helps it create a weak electric field. This electric field lets it locate its prey without needing to see them. Adults can grow quite large, reaching up to 1.6 metres (about 5.2 feet) long and weighing as much as 19 kilograms (about 42 pounds).

In 1950, a scientist named Hans Lissmann discovered that this fish could swim just as well forwards or backwards, showing it must use something other than eyesight to find its way. He proved that the aba uses electroreception to sense its surroundings, making it the first fish known to have this amazing ability. In West Africa, where the fish is commonly found, it is considered a valuable food source and plays an important role in culture. It is often given as a gift during celebrations and marriages. While the aba is not in danger globally, local areas in West Africa face threats from overfishing and pollution.

Taxonomy

Gymnarchus niloticus was first described by Georges Cuvier in 1829. The family Gymnarchidae was created by Pieter Bleeker in 1859. This family is closely related to another group of electric fishes called the Mormyridae. Both groups can produce weak electric fields. The oldest fossils of Gymnarchus come from the time of the Middle Eocene in Libya.

Biology

Gymnarchus niloticus is a special kind of fish that belongs to a group called bony-tongue fishes. It has a long, slim body with brown and grey on top and a white belly. It has small gills on both sides and must breathe air because it can't get enough oxygen from water alone. This fish has a single lung on the right side of its body.

Unlike most fish, Gymnarchus niloticus doesn't have pelvic or anal fins. Instead, it has a tail fin that looks like a rat's tail. Its main fin on the back helps it move, allowing it to swim forward and backward easily. Adult fish can grow up to 1.6 metres long and weigh as much as 19 kilograms.

This fish can't see well at night, so it uses a weak electric field to find its way and hunt for food. It creates this electric field around its body, which helps it sense nearby objects by how they change the field. This special ability was first discovered by a scientist in 1950. The fish uses this electric sense to find smaller fish and other tiny animals to eat, whether it's young or fully grown. It lives at the bottom of rivers and lakes in fresh water.

When it's time to have babies, these fish build big nests in flooded areas during the rainy season. The female lays many large eggs in the nest, and both parents watch over the young until they are ready to explore on their own.

Distribution

Gymnarchus niloticus lives in freshwater lakes and rivers in Africa. You can find this fish in the Nile, Turkana, Chad, Niger, Volta, Senegal, and Gambia areas. It is only found in these tropical waters.

Conservation status

The conservation status of this fish is not very clear. The IUCN Red List last checked it in 2019 and said it was 'least concern'. However, in Nigeria it is listed as an endangered species. This is because of things like destruction of habitat, overfishing, and other human activities near the river. Young fish are often caught with their parents and do not survive in captivity, which is another problem. Threats to this fish include pollution, changes to the water system, and climate change.

Human use

Food

The aba, also called the frankfish, is a popular food in several West African countries because it tastes good and has a lot of meat. People often eat it raw or smoked, and its large eggs can be eaten too. Because it grows quickly and is in demand, it could be a great fish for aquaculture farming.

In the Yoruba culture of West Africa, this fish is important for special events like weddings and celebrations. It is often given as a gift from someone asking to marry to the bride's family, or to leaders during festivities.

Biomimetic inspiration

Scientists studied how this fish swims in a special way, which led to the creation of a robotic fin called RoboGnilos. This robot helps researchers learn more about the fish's swimming movements.