Guinean Bichir

Guinean bichir（Polypterus ansorgii ）drawing（圖片來源：Boulenger, George Albert，CC0 1.0 公共領域。）

The Guinean bichir (Polypterus ansorgii) is a member of the family Polypteridae within the order Polypteriformes of the class Actinopterygii. It is a predatory species commonly found in the aquarium trade. Because of its primitive appearance and body structure that differs markedly from most other bony fishes, it is widely known in the aquarium market as a “dinosaur fish.” In Chinese-speaking markets it is commonly called Ansorge's dinosaur bichir or Ansorge's dinosaur fish, while in English it is usually referred to as the Guinean bichir or Ansorge's bichir.

Morphology

In terms of appearance, the Guinean bichir possesses one of the defining characteristics of the family Polypteridae: multiple separated dorsal finlets. These small dorsal fin spines are among the most important features used to identify bichirs. Individuals typically possess approximately 13–15 dorsal finlets. The upper and lower jaws are nearly equal in length, which is also an important trait for species identification.

In addition, unlike most ray-finned fishes, the Guinean bichir retains many traits characteristic of early actinopterygians. One example is the presence of distinctive ganoid scales. These scales consist of a heavily mineralized ganoine outer layer, a dentine-like cosmine layer, a vascular layer containing medullary cavities, and an inner bony layer composed of parallel bone plates known as isopedine.

Because its natural habitat consists of plant-rich swampy waters, the Guinean bichir has evolved a cylindrical body and flattened head suited for navigating complex benthic environments. To survive in swamps and lakes where wet and dry seasons are strongly pronounced, this group of fishes has also independently evolved structures similar to those seen in lobe-finned fishes, including spiracles and a modified swim bladder that functions in air breathing. These adaptations allow them to temporarily leave drying pools during the dry season and move to more suitable bodies of water.

In coloration, adult Guinean bichirs possess large dark blotches along the sides of the body. In terms of size, the species is considered a medium-sized predatory fish. The maximum standard length recorded from museum specimens is approximately 28 cm.

Regarding development, members of the family Polypteridae differ from most other fishes in that juveniles possess distinctive external gills. These structures give them an appearance similar to amphibian larvae. The exact evolutionary reason for the development of such external gills remains unclear, but it is known that these gills gradually regress and disappear as the fish grows.

Native Range and Habitat

The Guinean bichir is native to the Corubal River in Guinea-Bissau in West Africa, with additional records from Guinea and Nigeria. It primarily inhabits freshwater rivers and slow-flowing waters within the region.

As an ambush predator, the Guinean bichir prefers areas with slow current, shallow zones, dense vegetation, or muddy and sandy substrates. When dissolved oxygen levels decline, the fish can supplement oxygen intake by breathing atmospheric air using its lung-like respiratory system.

Aquarium Conditions

The Guinean bichir is a medium-sized predatory fish and is generally recommended to be kept individually. Housing it together with small fishes or other large aggressive predators is not recommended. If a mixed aquarium is desired, it should be limited to large and relatively peaceful species.

Aquariums are best designed according to the adult size of the fish. A single individual should be provided with a tank volume of at least 300–500 liters to allow sufficient turning space. Larger custom aquariums are required if multiple individuals are to be kept together. Bichirs are powerful jumpers, so aquariums must be fitted with a tightly sealed yet ventilated lid to prevent escape during stress or while surfacing to breathe.

In terms of environmental design, the Guinean bichir is a typical ambush predator that prefers shaded or sheltered areas. Aquarium setups should therefore include driftwood, caves, dense plants, or floating vegetation to provide cover. A substrate of sand or fine gravel is recommended. Direct exposure to strong lighting should be avoided, as excessive brightness can cause stress.

Guinean bichir（圖片來源：Ooi Hong Liang，採用 CC BY-NC 4.0 授權）

Water parameters should ideally be maintained at 24–28°C with neutral to slightly acidic conditions (approximately pH 6.5–7.5). Water movement should remain gentle, and strong currents should be avoided. Because bichirs are benthic carnivores that produce considerable leftover food and organic waste, efficient filtration is essential. Regular water changes are also required, typically around 20–30% per week depending on water quality. A filtration system combining biological filtration with mechanical filtration is recommended.

Feeding Conditions

The Guinean bichir is a bottom-dwelling carnivore. In nature it feeds primarily on small fishes, crustaceans, earthworms, insects, and aquatic invertebrates. In captivity it readily accepts sinking carnivorous pellets as well as frozen foods such as bloodworms, shrimp, and pieces of fish. A varied diet is recommended to maintain balanced nutrition.

Adult individuals are typically fed once per day or every other day, depending on their activity level and appetite. Juveniles require more frequent feeding, usually one to two times per day. Feeding is best conducted under dim lighting or during dusk and nighttime hours, as bichirs are largely nocturnal and tend to feed more actively in low-light conditions.

Breeding Conditions

Information on reproduction in the wild is relatively limited. However, aquarium records indicate that successful captive breeding has been achieved in recent years, particularly in breeding facilities in Indonesia and other parts of Southeast Asia. Breeding generally requires specialized setups and a staged approach consisting of a spawning environment, an egg-transfer or incubation system, and a rearing stage for juveniles.

Bichirs typically deposit eggs in areas with fine sand or soft substrates combined with low-growing, fine-leafed aquatic plants such as Java moss. After spawning, plants carrying the eggs are usually transferred to a separate hatching tank with water temperatures around 27–28°C and pH values between 6.5 and 7 to improve hatching success. Adult fish may consume eggs or fry, so separating the breeding adults from the eggs is necessary. Plants and incubation tanks should provide sufficient protection during the egg and hatching stages.

Preventing Invasive Spread

The Guinean bichir originates from Africa and is a highly adaptable carnivorous species. Released individuals can easily become invasive in non-native environments and may threaten local ecosystems. They are capable of preying upon the eggs and juveniles of native fishes while also competing for food resources, potentially disrupting local fish populations.

Aquarists must therefore follow the principle of responsible ownership and never release unwanted fish into natural waterways. Under no circumstances should Guinean bichirs be introduced into the wild. If an owner can no longer care for the fish, it should be rehomed through other aquarists or transferred to an aquarium facility willing to accept it.

Author: Rodrigo

References:

1. FishBase. (n.d.). Polypterus ansorgii summary. Retrieved from FishBase database.

2. GBIF Secretariat. (n.d.). Polypterus ansorgii Boulenger, 1910. GBIF Backbone Taxonomy.

3. Polypterus.info. (n.d.). Keeping Polypterus — husbandry and feeding notes.

4. Aquarium Glaser GmbH. (n.d.). Polypterus ansorgii (Guinean bichir) — trade / breeding notes.

5. AquaInfo / Aquainfo.org. (n.d.). Polypterus ansorgii — Guinea Bichir (care & breeding tips).

6. Taiwan Fisheries / TFRI & MOA species pages