Senegal Bichir

Senegal bichir（Polypterus senegalus）（圖片來源：ictheostega，採用 CC BY 4.0 授權。）

The Senegal bichir (Polypterus senegalus) is a member of the family Polypteridae within the order Polypteriformes of the class Actinopteri (ray-finned fishes). It is a predatory fish commonly encountered in the aquarium trade. Because of its highly primitive appearance and body structure that differs markedly from most modern teleost fishes, it is often called a “dinosaur fish” in the aquarium market. In Chinese-speaking regions it is commonly known as the “gold dinosaur fish,” while in English-speaking markets it is referred to as the Senegal bichir, gray bichir, or Cuvier's bichir.

Morphology

Externally, the Senegal bichir displays the most distinctive trait of the family Polypteridae: a series of separate dorsal finlets along the back. These dorsal finlets are one of the most important diagnostic characters used to identify bichirs. Individuals typically possess 8–11 dorsal finlets, with 11–17 anal fin rays. The vertebral count ranges from 53 to 59, and the upper and lower jaws are approximately equal in length. These traits are key features used in species identification.

Compared with most ray-finned fishes, bichirs retain numerous ancestral features of early actinopterygians. One example is their distinctive ganoid scales. These scales consist of a highly mineralized outer layer called ganoine, a dentine-like layer resembling cosmine, a vascular layer containing a pulp cavity, and an inner layer known as isopedine formed by parallel bony plates.

Because their natural habitats are densely vegetated swamp environments, bichirs have evolved a cylindrical body shape and a flattened head that allow them to navigate complex bottom substrates. To survive in swamps and lakes that experience pronounced wet and dry seasons, these fishes have also evolved structures convergent with those of lobe-finned fishes, including spiracles and a modified swim bladder that functions as a lung. These adaptations allow them to supplement oxygen by breathing air and to move temporarily across land during drought periods in search of new water bodies.

In coloration, adult Senegal bichirs are olive on the dorsal side with a white underside. The flanks lack mottled or marbled patterns, and the fins are generally gray. In terms of body size, the Senegal bichir is considered a medium-sized predatory fish, reaching a total length of up to approximately 32 cm.

Whole-body view of a wild-type Senegal bichir（圖片來源：H.Grenier，採用 CC BY-NC 4.0 授權。）

Growth and development in the family Polypteridae differ from those of most other fishes. Juvenile bichirs possess distinctive external gills that resemble those of amphibian larvae. The evolutionary reason for the development of these unusual external gills is not yet fully understood. However, it is known that the external gills gradually regress and disappear as the fish matures.

Native Range and Habitat

The Senegal bichir occurs in the middle and lower reaches of the Congo River basin in Africa. It inhabits streams, swamps, and slow-moving waters with dense vegetation. These fishes primarily occupy freshwater rivers and areas with gentle currents.

As ambush predators, bichirs prefer habitats with slow flow, shallow areas, abundant vegetation, and muddy or sandy substrates. When dissolved oxygen levels decline, they can supplement oxygen intake through air breathing using their lung-like swim bladder.

Aquarium Conditions

The Senegal bichir is a medium-sized predatory fish. It is generally recommended to keep individuals singly rather than with smaller fish or large aggressive predators. If a community setup is desired, it is best to house them with large, relatively peaceful species.

Aquarium size should be based on the adult size of the fish. A single individual should be provided with a tank of at least 300–500 liters in volume, with a minimum length of 120 cm, allowing sufficient space for turning and movement. If multiple individuals are to be kept together, a larger custom aquarium is required.

It is important to note that bichirs are powerful jumpers. When designing the aquarium, a secure yet ventilated lid should be installed to prevent the fish from jumping out due to stress or while surfacing for air.

In terms of habitat layout, bichirs are classic ambush predators that prefer dimly lit or sheltered areas. Aquascaping should include driftwood, caves, dense vegetation, or floating plants to provide cover. The substrate should consist of sand or fine gravel. Strong direct lighting should be avoided, as it may induce stress.

Senegal bichir aquarium setup and community tank conditions（圖片來源：TVRGolf，採用 CC BY-NC 4.0 授權。）

Water parameters should generally be maintained at temperatures between 24 and 28°C. The pH should range from neutral to slightly alkaline (approximately pH 6.0–7.8). Water movement should be gentle or moderately filtered, and strong currents should be avoided.

Because bichirs are benthic carnivores that produce substantial leftover food and organic waste, efficient filtration is essential. Regular water changes are recommended, typically around 20–30% per week depending on water quality. A filtration system combining mechanical and biological filtration is ideal.

Feeding Conditions

Bichirs are bottom-dwelling carnivores. In the wild they feed primarily on small fish, crustaceans, earthworms, insects, and other aquatic invertebrates. In aquaria they readily accept sinking carnivore pellets as well as frozen foods such as bloodworms, shrimp, and fish flesh.

A varied diet is recommended to maintain balanced nutrition. Adult individuals are typically fed once per day or every other day, depending on activity level and appetite. Juveniles require more frequent feeding, usually one to two times daily.

Feeding is most effective under dim lighting or during dusk and nighttime, as bichirs are generally nocturnal and more active in low-light conditions.

Breeding Conditions

The Senegal bichir is an egg-laying species that scatters slightly adhesive eggs, which attach to plants or other structures. A single spawning event may produce several dozen to several hundred eggs depending on the species and conditions.

Fertilization occurs externally. During spawning, the male wraps around the female and assists in releasing sperm to fertilize the eggs. The eggs typically hatch within approximately 3–7 days, depending on water temperature.

Early larvae feed on planktonic or very small benthic prey. Juveniles may possess external gills during the early stages of development.

Successful captive breeding has been documented in the aquarium trade, and in some regions captive-bred individuals are now commercially available. For breeding attempts, it is recommended to provide abundant aquatic plants or spawning mops, maintain stable water conditions, and simulate seasonal environmental changes such as fluctuations in temperature or water level to stimulate spawning.

During the incubation period, antifungal precautions should be taken, such as the careful use of methylene blue. Newly hatched larvae should be provided with microscopic live foods, including protozoans, micro-rotifers, or newly hatched brine shrimp.

Preventing Invasive Spread

The Senegal bichir is native to Africa and is a highly adaptable carnivorous fish. If released into non-native environments, abandoned individuals may become invasive species and threaten local ecosystems. They may prey upon the eggs and larvae of native fishes and compete with indigenous species for food resources.

For this reason, aquarists must strictly follow the principle of “no release and no abandonment.” Under no circumstances should Senegal bichirs be released into natural waterways.

If an owner can no longer care for the fish, it should be rehomed to another aquarist or transferred to an aquarium facility willing to accept it.

Author: Rodrigo

References:

1. Cuvier, G. (1829). Le règne animal distribué d'après son organisation (rev. & augm. ed., Vol. II). Chez Déterville. (Original description of Polypterus senegalus).

2. Froese, R., & Pauly, D. (Eds.). (2025). Polypterus senegalus Cuvier, 1829. In FishBase. Retrieved September 13, 2025, from https://www.fishbase.se/summary/Polypterus-senegalus.html

3. SeriouslyFish. (n.d.). Polypterus senegalus (Senegal bichir) — species account. Retrieved September 13, 2025, from https://www.seriouslyfish.com/species/polypterus-senegalus/

4. GBIF Secretariat. (2025). Polypterus senegalus Cuvier, 1829. GBIF Backbone Taxonomy. Retrieved September 13, 2025, from https://www.gbif.org/species/108892669

5. IUCN Species (if needed — check latest assessment): Moelants, T. (year). Polypterus senegalus. The IUCN Red List of Threatened Species. Retrieved September 13, 2025, from https://www.iucnredlist.org

6. Moritz, T., & Britz, R. (2019). Revision of the extant Polypteridae (Actinopterygii: Cladistia). Verlag Dr. Friedrich Pfeil. (taxonomy / species concepts)