Reedfish (Ropefish)
- Rodrigo
- Mar 15
- 5 min read
The reedfish (Erpetoichthys calabaricus) is a member of the class Actinopterygii, order Polypteriformes, and family Polypteridae. It is a predatory species commonly encountered in the aquarium trade. Because of its extremely primitive appearance and its body structure that differs markedly from most other bony fishes, it is often referred to in the aquarium market as a “dinosaur fish.” In the Chinese aquarium trade it is commonly called the grass rope dinosaur, while in the English-speaking market it is widely known as the reedfish, ropefish, snakefish, or rope eel.
Behavior and Ecology
In the wild, reedfish function as ambush predators. They typically inhabit slow-moving waters with dense vegetation, muddy or sandy substrates, and shallow areas where prey animals are abundant. Their elongated bodies allow them to move through thick aquatic plants and complex bottom structures with ease.
Reedfish are capable of breathing atmospheric oxygen through lung-like organs derived from the swim bladder. When dissolved oxygen levels decline in the water, they can surface to gulp air, allowing them to survive in habitats where oxygen concentrations fluctuate seasonally. This adaptation is particularly advantageous in swamps, floodplains, and shallow lakes where dry seasons may temporarily reduce water levels or oxygen availability.
Morphology
Reedfish possess one of the most distinctive traits of the Polypteridae: multiple separated dorsal finlets along the back. These dorsal finlets, usually numbering about 8–12, are among the most recognizable diagnostic features of bichirs and their relatives. The anal fin contains approximately 9–13 soft rays.
The head bears short nasal barbels, and the snout extends slightly beyond the lower jaw. The pectoral fins are well developed, while pelvic fins and the subopercular bone are absent. The body is extremely elongated and cylindrical, giving the fish a snake- or eel-like appearance, which serves as an important identifying characteristic within the species.
Unlike most ray-finned fishes, polypterids retain numerous ancestral features. One example is the presence of ganoid scales. These scales consist of several structural layers: a heavily mineralized ganoine outer layer, a dentine-like cosmine layer beneath it, a vascular layer containing internal cavities, and an inner isopedine layer composed of parallel bony plates.
Because reedfish naturally inhabit densely vegetated swamp environments, their slender cylindrical bodies represent an adaptation to maneuvering through complex benthic habitats. In addition, they have evolved spiracles and a modified swim bladder resembling the respiratory system of lobe-finned fishes, enabling them to survive seasonal drought conditions by briefly leaving drying pools and locating new water bodies.
Adult reedfish typically display a greenish-gray or olive-brown dorsal coloration, with a yellowish or orange underside. A distinct black patch is usually present on the fleshy base of each pectoral fin. In terms of size, reedfish are considered medium-small predatory fish, reaching a maximum length of about 37 cm.
During development, members of the family Polypteridae differ significantly from most fishes. Juveniles possess external gills that resemble those of amphibian larvae. The evolutionary reason for this unusual feature remains unclear. However, these external gills gradually regress and disappear as the fish matures.
Native Range and Habitat
Reedfish are native to West and Central Africa. Their distribution extends from the Ogun River delta in Nigeria to the Chiloango River basin in the Republic of the Congo (Congo-Brazzaville).
They inhabit streams, swamps, and slow-moving waters with dense aquatic vegetation. Most populations occur in freshwater rivers and calm waterways. As ambush predators, reedfish prefer environments with slow currents, shallow zones, abundant plant cover, and muddy or sandy substrates. When dissolved oxygen levels drop, they are able to supplement oxygen intake by breathing air.
Housing Requirements in Captivity
Reedfish are medium-sized predatory fish and are generally recommended to be kept individually. They should not be housed with small fish or highly aggressive large predators. If mixed-species housing is desired, they are best kept with large, peaceful fish species.
Aquaria should be designed according to the adult size of the fish. A single individual requires at least a 300–500 liter aquarium with a minimum length of about 120 cm to allow sufficient space for turning and movement. Larger tanks are necessary if multiple individuals are kept together.
Reedfish are extremely capable jumpers. Aquaria must therefore be equipped with tightly fitted yet well-ventilated lids to prevent escape, especially when the fish become stressed or surface to breathe.
In terms of environmental design, reedfish are classic ambush predators that prefer dark or sheltered spaces. Aquaria should contain driftwood, caves, dense vegetation, or floating plants to provide cover. Substrates composed of sand or fine gravel are recommended. Strong direct lighting should be avoided, as it may cause stress.
Water temperature should be maintained between 24–28°C, with water chemistry ranging from neutral to slightly alkaline (approximately pH 6.5–7.8). Gentle water flow or mild filtration circulation is preferred; strong currents should be avoided.
Because reedfish are benthic carnivores that produce significant food waste and organic debris, efficient filtration is essential. Frequent partial water changes are recommended, such as replacing 20–30% of the water weekly or adjusting according to water quality. A combination of biological and mechanical filtration systems is ideal.
Feeding Conditions
Reedfish are bottom-dwelling carnivores. In the wild they feed on small fish, crustaceans, worms, insects, and other aquatic invertebrates. In captivity they can also accept sinking carnivore pellets and frozen foods such as bloodworms, shrimp, and fish meat.
A varied diet is recommended to maintain balanced nutrition. Adult individuals are usually fed once per day or every other day, depending on their activity level and appetite. Juveniles require more frequent feeding, typically once or twice daily.
Feeding is best conducted under dim lighting or during dusk and nighttime hours, as reedfish are primarily nocturnal and feed more actively under low-light conditions.
Breeding Conditions
Reedfish reproduce by spawning. The eggs are scattered and slightly adhesive, attaching to plants or artificial structures. The female deposits small batches of eggs between the male's pelvic and anal fins where fertilization occurs, after which the eggs are dispersed among aquatic plants or substrates.
The incubation period is short, lasting only several days. The larvae retain external gills for several weeks after hatching.
Although there have been occasional breeding reports within the aquarium community, captive reproduction is generally considered moderately difficult. Most successful cases come from experienced breeders, as both spawning and larval rearing require specialized equipment and careful management.
If breeding is attempted, providing abundant plants or spawning mops, maintaining stable water conditions, and simulating seasonal environmental changes such as temperature shifts or water-level fluctuations may help trigger spawning. During incubation, antifungal measures such as the careful use of methylene blue may be beneficial. Newly hatched larvae should be provided with microscopic live foods such as protozoans, rotifers, or newly hatched brine shrimp.
Preventing Invasive Spread
Reedfish originate from Africa and possess strong ecological adaptability as carnivorous predators. If released into non-native environments, abandoned individuals may establish populations and become invasive species that threaten local ecosystems.
They may prey on the eggs and larvae of native fish and compete with indigenous species for food resources, potentially affecting the survival of native fish populations.
Aquarium keepers must therefore follow the principle of “no release and no abandonment.” Under no circumstances should reedfish be released into natural waterways. If owners can no longer care for their fish, they should rehome them to other aquarists or transfer them to aquariums or institutions willing to accept them.
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