Polypterus senegalus, commonly sold as the Senegal bichir or dinosaur bichir, is one of the hardiest and most unusual freshwater fish available to home aquarists. Its care is relatively straightforward compared to many exotic species, but its biology is genuinely strange: it breathes air through a pair of functional lungs, walks overland on muscular pectoral fins, and wears a suit of interlocking mineralized scales that researchers have studied as a model for engineered body armor. Getting the basics right means understanding that you are not keeping a typical aquarium fish. You are keeping something whose body plan has persisted, with modifications, for hundreds of millions of years, and whose needs in captivity reflect that deep history.
A Fish That Predates the Dinosaurs It Is Named After
The common name “dinosaur bichir” is catchy but misleading. Polypterus senegalus belongs to the order Polypteriformes, a lineage of ray-finned fishes whose evolutionary position has been debated since the era of Darwin and Huxley. There is now consensus that polypterids sit within the superorder Actinopterygii, but whether they represent the earliest branching lineage of ray-finned fishes or a closer relative of sturgeons and paddlefish remains an open question. A molecular study using the nuclear gene for proopiomelanocortin found that P. senegalus grouped with sturgeons and paddlefish rather than with more derived ray-finned fishes, suggesting the relationship might be closer than traditionally assumed.1PubMed. Characterizing a proopiomelanocortin cDNA cloned from the brain of the Bichir, Polypterus senegalus: evaluating phylogenetic relationships among ray-finned fish Either way, the polypterid lineage is ancient enough that calling this fish a “living fossil” is common shorthand in the hobby, even if biologists tend to avoid that term because the modern species is not identical to its ancestors.
For the keeper, the evolutionary backstory matters mainly because it explains the fish’s unusual anatomy. The lungs, the fleshy pectoral fins, the ganoid scales, and the larval external gills are not novelties. They are ancestral features retained from a time before the body plans of modern teleost fishes had taken shape. Every one of those features has a direct implication for how you set up and maintain the tank.
Tank Size and Setup
Adult Senegal bichirs typically reach 25 to 30 centimeters (roughly 10 to 12 inches) in captivity, though individuals occasionally grow a bit larger with excellent care. A single adult needs a tank of at least 90 gallons, and larger is always better. Because bichirs are bottom-dwellers that spend their active hours cruising along the substrate, floor space matters more than water depth. A long, wide tank outperforms a tall, narrow one. A 120-gallon breeder-style aquarium is a popular choice among experienced keepers.
Substrate should be smooth sand or fine rounded gravel. Bichirs drag their bellies across the bottom constantly, and sharp or jagged substrate can abrade their ventral surface and lead to secondary bacterial infections. Decorations that provide hiding spots during the day are essential. PVC pipes, driftwood caves, and dense plantings of hardy species like Anubias or Java fern all work well. Bichirs are not diggers or plant destroyers, but they will uproot anything that is not anchored or weighted down simply by bulldozing through it.
Lighting should be subdued. P. senegalus is a nocturnal ambush predator with low spatial visual acuity, relying far more on smell and lateral-line detection than on sight.2PubMed. Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus, as estimated by optokinetic response Bright overhead lights will stress the fish and keep it hidden all day. Dim lighting or a period of reduced light in the evening encourages more natural activity, and many keepers find that a moonlight LED brings out the best behavior.
Why the Lid Is the Most Important Piece of Equipment
No aspect of bichir husbandry gets more emphasis in experienced keeper communities than the lid. Polypterus senegalus can and will leave the water. This is not a once-in-a-lifetime event caused by panic. It is a behavior deeply embedded in the species’ biology. Bichirs walk over land using their muscular pectoral fins in a coordinated gait, and research has shown that when P. senegalus are raised in terrestrial conditions, their pectoral fin muscles undergo functional changes: the muscles operate at longer lengths, contract faster, and sustain activity longer compared to swimming, suggesting the locomotor system is surprisingly well adapted to overland movement.3PubMed Central. Walking elicits muscle functional changes in the pectoral fin of Polypterus senegalus Even more striking, fish reared on land for extended periods show measurable changes in the shape of their pectoral girdle, the bony structure supporting the fins, demonstrating a degree of skeletal plasticity in response to habitual terrestrial locomotion.4The FASEB Journal. 3D geometric morphometric analysis of phenotypic plasticity in the pectoral girdle of a basal actinopterygiian fish
In practical terms, this means your tank needs a tight-fitting lid with no gaps larger than a centimeter or two. Bichirs are strong and surprisingly flexible. They can push through loose-fitting lids, squeeze out of gaps around filter intakes or heater cords, and climb wet silicone seams in the corners of aquariums. Many keepers have found their bichir on the floor, sometimes rooms away from the tank. A dried-out bichir can survive for a surprisingly long time out of water thanks to its lungs, but the experience is stressful and the risk of injury from the fall is real. Weight down the lid, seal every opening, and assume the fish is actively testing every potential escape route. Because it is.
Air Breathing and What It Means for Water Depth
Bichirs are obligate air breathers. They possess paired ventral lungs, not a swim bladder repurposed for occasional gas exchange, but true lungs homologous to those of tetrapods. The breathing cycle is complex and fascinating. The fish rises to the surface, aligns its head with the air-water interface, and expels spent lung gas through its mouth and opercular slits. Fresh air is then drawn in through the spiracles, a pair of valve-covered openings on top of the head, and forced into the lungs by compression of the mouth chamber.5Nature Communications. Spiracular air breathing in polypterid fishes and its implications for aerial respiration in stem tetrapods This spiracular inhalation system is unique among living fishes and may represent an ancestral mode of air breathing that preceded the mouth-based gulping seen in lungfishes and many other air-breathing fish groups.
The care implication is straightforward: your bichir must have unobstructed access to the water surface. Tanks with very deep water columns are not ideal unless the fish has clear vertical pathways to the top. Dense floating plant cover that completely blocks the surface can become a hazard if it prevents the fish from breathing. A small open area should always be maintained. You will notice your bichir rising to gulp air regularly throughout the day and night, often every few minutes in warm water. This is normal and not a sign of poor water quality, though increased air-breathing frequency in a fish that was previously calm can sometimes indicate oxygen depletion or stress.
Because they can extract oxygen from the atmosphere, bichirs tolerate stagnant, low-oxygen water better than most fish. In the wild, they inhabit swamps, floodplains, and slow-moving marginal habitats across tropical Africa. This tolerance does not mean you should keep them in dirty water. It means they are forgiving of imperfect aeration, which is a useful trait for a large predatory fish that produces significant waste.
Water Parameters
Senegal bichirs are broadly tolerant of water chemistry. They do best in warm water between 25 and 28°C (77 to 82°F). A pH range of 6.5 to 7.5 is ideal, though they handle mild deviations without visible stress. Hardness is not critical, and most tap water in the moderate range works fine. Ammonia and nitrite must be kept at zero, as with any fish, and nitrates should stay below 40 ppm through regular water changes. A 25 to 30 percent weekly water change is a good baseline for a tank housing one or two bichirs alongside moderate filtration.
Filtration should prioritize biological and mechanical capacity over water flow. Strong currents are not appreciated. Bichirs are slow swimmers that rely on their pectoral fins for low-speed maneuvering, beating the fins rhythmically in phase to generate gentle propulsive force.6Integrative and Comparative Biology. The Water to Land Transition Submerged: Multifunctional Design of Pectoral Fins for Use in Swimming and in Association with Underwater Substrate A canister filter with a spray bar diffusing the output along the back wall, or a large sponge filter, both work well. Avoid powerheads pointed directly at the bottom of the tank where the bichir rests.
Feeding a Smell-Driven Predator
Feeding bichirs is one of the easier parts of their care, but understanding how they find food helps you do it well. Bichirs are primarily olfactory hunters. Their nostrils are housed in forward-projecting tubes that give the head its distinctive look, and these organs are remarkably sensitive. Research on feeding behavior in P. senegalus found that the fish approaches potential food items by bringing its nasal tubes close to the object and sniffing before deciding whether to eat. When food pellets were scented with chironomid (bloodworm) extract, the fish responded faster and more reliably than to unscented pellets.7Journal of Ichthyology. Orosensory Preferences and Feeding Behavior of Cladistia: A Comparison of Gray Bichir Polypterus senegalus and Saddle Bichir P. endlicherii (Polypteridae) The visual acuity findings mentioned earlier reinforce this: bichirs do not hunt by sight the way a cichlid or a bass does.2PubMed. Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus, as estimated by optokinetic response
In captivity, a varied diet works best. Good staple options include sinking carnivore pellets, frozen bloodworms, frozen prawns or shrimp pieces, earthworms, and small pieces of tilapia or other white fish. Live foods like blackworms and earthworms are eagerly accepted and provide enrichment. Bichirs are messy eaters that tend to grab food and thrash, scattering debris around the tank, so siphoning uneaten scraps after feeding is a good habit. Feed every one to two days for adults. Juveniles growing rapidly benefit from daily meals.
Because bichirs feed primarily at night or in dim conditions, dropping food in during the evening or just after lights-out improves the chance that your bichir gets its share before faster tankmates do. Many keepers target-feed with long tweezers or a turkey baster, placing food directly in front of the bichir’s nose. The fish will sniff it, pause, and then lunge. It is a distinctly different feeding style from most aquarium fish and one of the endearing behaviors that draws people to the species.
Tank Mates
Senegal bichirs are predatory but not aggressive in the territorial sense. They will eat anything that fits in their mouth, which is wider than it looks, but they generally ignore fish too large to swallow. Good tank mates include medium to large peaceful species: larger tetras (silver dollars, for example), medium-sized catfish like Synodontis species, large barbs, and non-aggressive cichlids. Other bichir species of similar size often coexist well, though competition for food and hiding spots can increase with more individuals.
Avoid keeping Senegal bichirs with small fish like neon tetras, guppies, or small rasboras. These will become expensive live food. Also avoid highly aggressive cichlids that might harass the bichir during the day when it is trying to rest. Bichirs are tough but slow, and a persistent fin-nipper can cause chronic stress and wounds. That said, their scales provide meaningful physical protection, a point worth exploring on its own.
Ganoid Armor and What It Tells You About Handling
The scales of P. senegalus are not the thin, flexible, overlapping scales of a typical aquarium fish. They are ganoid scales: thick, mineralized, multi-layered structures that interlock across the body like tiles. Researchers have studied these scales extensively as a model for bio-inspired armor. Each scale consists of a hard outer layer and softer, more compliant inner layers, forming a composite system that resists puncture while remaining flexible enough for the fish to swim and walk.8PubMed. Finite element modeling of multilayered structures of fish scales Simulations of biting attacks, specifically the kind of conspecific aggression that bichirs experience in the wild, show that the scale architecture is effective at defeating tooth penetration, distributing force, and dissipating energy across multiple layers.9PubMed. Threat-protection mechanics of an armored fish
For the keeper, this means two things. First, bichirs are physically tougher than most aquarium fish. Minor scrapes and bumps that would injure a scaled cichlid or a catfish are often absorbed by the ganoid armor without lasting damage. Second, their rough texture makes netting them more difficult. The scales snag easily in fine mesh nets, and struggling to free a tangled bichir can damage both the net and the fish’s fins. A large, wide-mouthed container or a wet hand (with gloves, if preferred) is a safer way to move them.
Common Health Concerns
Senegal bichirs are robust fish that rarely fall ill in well-maintained tanks, but a few issues come up more often than others.
Monogenean parasites are a known concern. Macrogyrodactylus polypteri is a viviparous (live-bearing) flatworm parasite found on the skin and fins of P. senegalus.10Journal of Helminthology. Further Studies on Macrogyrodactylus polypteri, a Monogenean on the African Freshwater Fish Polypterus senegalus Wild-caught bichirs are particularly likely to carry these parasites, which can cause irritation, excessive mucus production, and flashing (rubbing against objects). Quarantine and prophylactic treatment of wild-caught specimens with praziquantel is standard practice among experienced bichir keepers. Captive-bred fish are less likely to arrive parasitized but not immune to infection if introduced to a tank with contaminated water or tankmates.
Bacterial infections of the skin and fins are the second most common issue, usually secondary to poor water quality, substrate abrasion, or injuries from tankmates. Because bichirs rest on the bottom, a dirty substrate is a direct health hazard. Regular gravel vacuuming during water changes is important. If you notice reddened patches on the belly, frayed fins, or fuzzy growths on the skin, a course of broad-spectrum antibacterial treatment (following local regulations for aquarium antibiotics) combined with improved water quality usually resolves the problem.
Overfeeding is a subtler risk. Bichirs are opportunistic and will eat as much as you offer. Obese bichirs develop fatty liver disease over time, which shortens their lifespan. In good conditions, Senegal bichirs can live 15 to 20 years or longer. Keeping them lean with moderate, regular feeding rather than sporadic large meals is one of the simplest ways to ensure a long life.
Breeding and Larval Development
Breeding P. senegalus in captivity is achievable but not common among casual hobbyists. Spawning is seasonal in the wild, triggered by the onset of the rainy season with its associated drop in water hardness, slight temperature shifts, and increased flooding of marginal habitats. In captivity, keepers simulate this with large water changes using slightly cooler, softer water, combined with a period of reduced feeding followed by heavy conditioning with live and frozen foods.
Males develop a thickened, fan-shaped anal fin during breeding condition, which they use to cup and receive eggs from the female. The eggs are scattered among fine-leaved plants or spawning mops. Hatching occurs within a few days at tropical temperatures, and the larvae are tiny and initially helpless.
The most remarkable feature of bichir larvae is their external gills, feathery structures that protrude from the head and serve as the primary breathing organs before the lungs develop. Research has shown that these external gills are developmentally associated with the hyoid arch, the second segment of the skull, making them anatomically distinct from the external gills of amphibian larvae, which derive from the gill arches farther back. The hyoid segment undergoes an accelerated developmental schedule in bichir embryos, and the external gills are actually the first cranial structures to appear, emerging before the eyes or mouth are visible.11PubMed Central. Bichir external gills arise via heterochronic shift that accelerates hyoid arch development The gills are reabsorbed as the juvenile grows and transitions to lung-based air breathing.
Raising the fry requires live foods like baby brine shrimp and microworms, excellent water quality in a small, shallow rearing tank, and patience. Cannibalism among siblings is common as they grow at different rates, so size-sorting is necessary. Breeding bichirs is a rewarding project for the dedicated aquarist, but it demands significantly more effort than simply keeping adults.
The Regeneration Factor
One of the more quietly impressive abilities of Polypterus senegalus is its capacity for regeneration. Bichirs can fully regrow damaged or lost fins, a trait they share with zebrafish and axolotls and one that has drawn attention from biomedical researchers. A comparative multi-omics study used P. senegalus alongside zebrafish and axolotls as a model for understanding the conserved and species-specific mechanisms underlying appendage regeneration.12Nature Communications. Comparative multi-omic analysis reveals conserved and derived mechanisms of fin and limb regeneration For the keeper, regeneration means that minor fin damage from nipping tankmates or rough handling will usually heal cleanly in good water conditions without intervention. You may notice a fin growing back with a slightly different shape or coloration initially, but it typically normalizes over weeks to months.
This regenerative capacity does not extend to severe injuries like deep body wounds or lost eyes, so it is not an excuse for careless husbandry. But it does mean that the cosmetic damage common in community tank life, a torn pectoral fin, a ragged dorsal, rarely becomes a permanent problem in a well-maintained environment. Combined with their armored scales, their air-breathing backup, and their tolerance of imperfect water chemistry, regeneration rounds out a picture of a fish built to survive adversity. For the aquarist willing to provide the basics, a secure lid, a roomy tank, dim lighting, meaty food, and clean water, the Senegal bichir repays the effort with decades of fascinating, genuinely prehistoric behavior.