Congo Bichir
- Rodrigo
- Mar 15
- 6 min read
The Congo bichir (Polypterus congicus) is a member of the order Polypteriformes and the family Polypteridae within the class Actinopterygii. It is a predatory fish frequently encountered in the aquarium trade. Because of its primitive appearance and body structure that differs markedly from most other bony fishes, it is widely known as a “dinosaur fish.” In Chinese-speaking aquarium markets it is commonly called the “Golden Dinosaur King,” while in English it is generally referred to as the Congo bichir.
Morphology
In terms of external appearance, the Congo bichir possesses one of the defining characteristics of the Polypteridae: multiple separate dorsal finlets. These dorsal finlets are among the most important features used to identify bichirs. The Congo bichir typically has about 12–15 dorsal finlets. The pelvic fins are positioned toward the posterior half of the body, the lateral line contains approximately 46–52 scales, and the body is elongated, cylindrical in the anterior portion and laterally compressed toward the rear. The head is broad and flattened, the eyes are positioned on the upper sides of the head, and the lower jaw protrudes slightly. These features are important diagnostic characteristics within the species.
Unlike most other ray-finned fishes, bichirs retain many ancestral features of early actinopterygians. One example is their distinctive ganoid scales. These scales consist of several structural layers: a heavily mineralized outer layer known as ganoine, a dentine-like layer called cosmine, a vascular layer containing a medullary cavity, and an inner bony layer composed of parallel bone plates known as isopedine.
Because their original habitats consist of heavily vegetated swamp environments, bichirs have evolved a cylindrical body and flattened head suited to navigating complex bottom environments. In order to survive in swamps and lakes with pronounced wet and dry seasons, these fishes have also convergently evolved spiracles and a specialized swim bladder capable of functioning in air breathing, similar to those of lobe-finned fishes. These features allow them to temporarily leave drying pools during the dry season and move in search of more suitable aquatic habitats.
In terms of coloration, adult Congo bichirs range from gray to brown. Along the sides of the body there are typically seven to nine dark vertical bands. The overall coloration can become darker or lighter depending on environmental conditions. The Congo bichir is considered a large predatory fish, with a typical length of around 70 cm and a maximum recorded length reaching approximately 97 cm.
Growth and Development
Members of the family Polypteridae differ from most other fishes in that their juveniles possess external gills. These structures give the larvae an appearance somewhat similar to amphibian larvae. The evolutionary reason for the presence of these external gills is not yet fully understood. However, it is known that the external gills gradually regress and disappear as the fish grows.
Native Range and Habitat
The Congo bichir is mainly distributed in Central and West Africa, particularly within the Congo and Ogooué river basins. Records also exist from several other river systems across West and Central Africa. The species inhabits streams, swamps, and slow-moving waters rich in vegetation. It primarily occupies freshwater rivers and areas with gentle currents.
As an ambush predator, bichirs prefer habitats with slow water flow, shallow zones, dense vegetation, and substrates composed largely of mud or sand. When dissolved oxygen levels decline, they can supplement oxygen intake by breathing atmospheric air through their lung-like swim bladder.
Housing Requirements in Captivity
The Congo bichir is a large predatory fish and is generally recommended to be kept singly. It is not advisable to house it with small fish or other aggressive large predators. If community housing is attempted, it is best to combine it with large and relatively peaceful species.
Aquarium size should ideally be based on the adult size of the fish. A single individual typically requires an aquarium of at least 300–500 liters, with a minimum length of 120 cm, allowing sufficient space for turning and movement. If multiple individuals are kept together, a significantly larger aquarium is necessary.
It is important to note that bichirs are extremely capable jumpers. When designing or selecting an aquarium, a well-sealed yet ventilated lid should be installed to prevent the fish from jumping out of the tank during stress or while surfacing to breathe.
Regarding environmental structure, bichirs are typical ambush predators and prefer dim or sheltered areas. The aquarium can be arranged with driftwood, caves, dense plants, or floating vegetation to create hiding spaces. The substrate should consist of sand or fine gravel. Strong direct lighting should be avoided, as it may cause stress.
For water conditions, a temperature of 24–28°C is recommended, with water chemistry ranging from neutral to slightly alkaline (approximately pH 6.5–7.8). Gentle water flow or moderate filtration is preferable, and strong currents should be avoided.
Because bichirs are bottom-dwelling carnivores that produce relatively large amounts of leftover food and organic waste, frequent water changes are necessary. Weekly water changes of about 20–30 percent are recommended, although adjustments should be made according to water quality. An efficient filtration system combining biological and mechanical filtration is strongly advised.
Feeding Conditions
Bichirs are carnivorous bottom feeders. Their natural diet includes small fish, crustaceans, worms, insects, and various aquatic invertebrates. In captivity, they can also accept sinking carnivorous pellets and frozen foods such as bloodworms, shrimp, or pieces of fish.
Providing a varied diet is recommended to maintain balanced nutrition. Adult individuals are typically fed once per day or once every other day, depending on their activity level and appetite. Juveniles require more frequent feeding, generally one to two times per day.
Feeding is best conducted under dim lighting or during dusk or nighttime hours, as bichirs are largely nocturnal and tend to feed more actively under low-light conditions.
Breeding Conditions
The Congo bichir is an egg-laying species. The eggs are scattered during spawning and possess slight adhesiveness, allowing them to attach to plants or other surfaces. A single spawning event may produce from several dozen to several hundred eggs, depending on the species and individual.
Fertilization occurs externally. The male typically wraps around the female and assists in releasing sperm during spawning. Eggs usually hatch within approximately three to seven days, depending on temperature.
Newly hatched larvae initially feed on planktonic organisms or very small benthic prey. During the early developmental stage, the larvae possess external gills.
Although there are some reports of successful breeding within the aquarium hobby, artificial breeding of Congo bichirs is generally considered moderately difficult. Most successful cases come from experienced breeders. The breeding and larval-rearing stages require specialized equipment and considerable expertise, including the use of dedicated breeding tanks, protection of eggs and larvae, and careful management of larval food.
For those attempting to breed the species, providing large amounts of aquatic plants or spawning mops, maintaining stable water conditions, and simulating seasonal environmental changes such as temperature or water-level fluctuations may help trigger spawning. During the incubation period, antifungal treatments (for example, small amounts of methylene blue) may be used to protect the eggs. Newly hatched larvae should be provided with microscopic live foods such as protozoa, rotifers, or newly hatched brine shrimp.
Preventing Invasive Spread
The Congo bichir is native to Africa and is a highly adaptable carnivorous fish. If released into the wild, abandoned individuals can easily become invasive species and threaten local ecosystems. They may prey upon the eggs and larvae of native fish species and compete with them for food resources, ultimately affecting the survival of indigenous fish populations.
For this reason, aquarium keepers must strictly follow the principle of “no abandonment and no release.” Under no circumstances should Congo bichirs be released into natural waterways. If an owner can no longer keep the fish, it is recommended to transfer it to another aquarist. Alternatively, it may be surrendered to an aquarium facility willing to accept it.
Author: Rodrigo
References:
Moelants, T. (2010). "Polypterus congicus". IUCN Red List of Threatened Species. 2010 e.T182116A7805072. doi:10.2305/IUCN.UK.2010-3.RLTS.T182116A7805072.en. Retrieved 19 November 2021.
Froese, R.; Pauly, D. (2017). "Polypteridae". FishBase version (02/2017). Retrieved 18 May 2017.
Van Der Laan, Richard; Eschmeyer, William N.; Fricke, Ronald (11 November 2014). "Family-group names of Recent fishes". Zootaxa. 3882 (1): 1–230. doi:10.11646/zootaxa.3882.1.1. PMID 25543675.
Comments