Bichir (Polypterus senegalus)

What is a bichir?

The Senegal bichir (Polypterus senegalus) is one of the most ancient-looking fish you can keep in a freshwater aquarium. With a body that reaches up to 45 cm (18 in), a row of small isolated dorsal spines, thick interlocking ganoid scales, and a pair of functional primitive lungs, it belongs to a lineage that has barely changed in tens of millions of years. These are not decorative relics, however — bichirs are active, intelligent, and surprisingly personable for a fish that resembles a scale-armoured eel.

Sold under names like Senegal bichir, gray bichir, or dinosaur bichir, P. senegalus is the most beginner-accessible of the Polypterus genus. An albino morph (pink body, red eyes) is widely available and behaves identically to the standard form.

Where do bichirs come from?

Bichirs are native to West and Central Africa, distributed across a vast range that includes the Nile basin, the Chad basin, and the Niger and Senegal river systems. In the wild they inhabit shallow, warm, slow-moving or still floodplains, swamps, and river margins — environments that are often turbid, densely vegetated, and seasonally low in dissolved oxygen. That last point explains the primitive lung: when oxygen levels plummet during the dry season, a bichir can simply surface and breathe air directly.

This floodplain ecology explains two things: the bichir tolerates a wide range of water chemistry, and it evolved as a low-light, benthic ambush predator that hugs the substrate and uses paddle-like pectoral fins to stalk prey.

What size tank does a bichir need?

A single adult Senegal bichir needs a minimum of 300 L (79 gal), and that is a genuine minimum rather than a comfortable recommendation. At full size — 45 cm (18 in) — the fish needs horizontal swimming space more than height, so a long, shallow footprint (150 cm / 60 in or longer) is far more useful than a tall, narrow aquarium.

Use fine sand as the substrate. Bichirs spend most of their time with their belly to the bottom; rough gravel abrades the ventral surface and the delicate pectoral fins over time. Provide plenty of caves, pipe sections, driftwood, and flat rocks to create dark resting spots — a bichir without cover is a stressed bichir.

A tight-fitting, weighted lid is essential. Bichirs are notorious escape artists that can push through surprisingly small gaps. Leave a few centimetres of air space between the waterline and the lid: the fish must be able to surface and breathe. Dimmer lighting suits the species and encourages more daytime activity.

What water parameters do bichirs need?

• Temperature: 24–28 °C (75–82 °F)
• pH: 6.5–7.5
• Hardness: 5–19 dGH

The bichir’s wide natural range makes it one of the more forgiving predators in terms of water chemistry. What it will not tolerate is poor water quality — a heavily fed carnivore produces significant waste, and ammonia or nitrite spikes cause rapid deterioration. Robust mechanical and biological filtration is non-negotiable. Aim for a turnover rate of at least 6–8 times the tank volume per hour, but diffuse the outflow so current at the substrate level stays gentle. Weekly or biweekly partial water changes of 25–30% will handle the nitrate load from a meaty diet.

What do bichirs eat?

Bichirs are obligate carnivores with poor eyesight and an extraordinary sense of smell. In the wild they eat fish, amphibians, invertebrates, and anything else they can ambush at night. In the aquarium, feed:

• Sinking carnivore pellets — the most practical staple; choose a high-protein formulation
• Earthworms — a favourite and nutritionally excellent
• Whole prawns or mussel (shell-off, fresh or frozen)
• Oily fish pieces such as tilapia or smelt, fed sparingly as a supplement
• Live or frozen bloodworms as an occasional treat for smaller juveniles

Offer food at dusk or after lights-out when the fish is most active. Tongs or a feeding stick help train bichirs to accept food at a set location, which reduces mid-tank ambush behaviour toward tankmates. Young bichirs benefit from daily small meals; adults do well on three to four feedings per week, keeping waste manageable. Remove uneaten food promptly.

Avoid fatty mammalian meats such as beef heart. Nutritional deficiencies have been documented in bichirs fed a monotonous single-prey diet — variety matters.

Are bichirs aggressive — and what fish can live with them?

Bichirs are semi-aggressive in a straightforward way: anything that fits in the mouth is potential food. Small tetras, guppies, livebearers, and dwarf cichlids are at serious risk. Fish that are clearly too large to swallow are generally left alone.

Good companions include large cichlids (Oscar, green terror, large geophagus), large plecos and other armoured catfish, clown loaches, and larger barbs. Multiple bichirs often cohabit well together, though brief sparring can occur, particularly at feeding time — ensure every individual gets food. Fin-nipping species should be avoided; bichirs’ pectoral and dorsal spines are vulnerable to persistent nippers.

For a full breakdown of species-by-species compatibility, see Bichir tank mates.

How do you tell male and female bichirs apart?

Dimorphism is subtle but reliable in mature fish. Males have a distinctly broader and thicker anal fin used to cup the female’s vent during spawning. Females are more robust through the abdomen, especially when gravid. In juveniles under roughly 25 cm (10 in), reliable sexing by external inspection is not possible.

How do bichirs breed?

Breeding bichirs in captivity is rated hard and is relatively uncommon in the hobby outside of specialist breeders. The preconditions include a large, well-conditioned pair, a significant temperature drop followed by a rise to simulate seasonal cues, and typically a rainy-season simulation achieved by frequent large water changes with slightly cooler water.

Spawning is brief: the male wraps his anal fin around the female’s vent and fertilises small batches of eggs scattered onto fine-leaved plants. The parents show no brood care and will eat eggs and fry — a dedicated growout tank is required. Eggs hatch in approximately 3–4 days at 28 °C (82 °F); the larvae initially carry an external yolk sac and look remarkably like salamander larvae, with external gills that are gradually absorbed. First foods are micro-worms, artemia nauplii, and small bloodworms.

What are common bichir diseases?

Bichirs are hardy once established, but several conditions appear with some regularity:

• Hole-in-the-head (HITH): Pitting or erosion around the sensory pores on the head and lateral line. Associated with poor water quality, carbon overuse, and nutritional deficiency — improving diet variety and reducing nitrates is the primary intervention.
• Skin and fin infections (bacterial): Redness, ulceration, or fraying of the soft fins, typically following injury (escape attempts, tankmate damage, or gravel abrasion). Fine sand substrate and prompt wound attention reduce risk.
• Parasitic infections (ich, velvet, flukes): Bichirs can carry and succumb to common protozoan and fluke infestations, particularly on import. Quarantine new fish for at least 4 weeks before introduction.
• Constipation / internal blockage: From fatty foods or overly large prey. A varied diet and sensible meal sizing reduce incidence.

Health note: disease identification and medication dosing are beyond the scope of a care profile. Confirm symptoms against a reputable veterinary or fish-health source before medicating — and note that bichirs, as scaleless-adjacent fish with ganoid scales, can show sensitivity to certain treatments.

How long do bichirs live?

A well-cared-for Senegal bichir lives 10–25 years in captivity — among the longest lifespans of any commonly kept freshwater fish. That longevity is the most important thing a prospective keeper needs to understand: this is a multi-decade commitment. Stable water chemistry, a varied carnivore diet, a correctly sized tank, and suitable tankmates are what deliver those years. Give a bichir those conditions and it will very likely outlast most of the other fish in your collection.