Classic Car Intelligence
  • Species: Polypterus ornatipinnis

  • Species: Polypterus palmas

  • Species: Polypterus senegalus

  • Species: Polypterus endlicheri endlicheri

  • Species: Erpetoichthys calabaricus

How to keep Bichirs

28 July 2017


Bichirs, also known as dinosaur eels, are primitive fish from the rivers and lakes of Africa. There are currently eighteen species and subspecies recognised, including Erpetoichthys calabaricus, better known as the Ropefish or Reedfish. All the other species belong to the genus Polypterus, and these range in size from around 30 cm (12 inches) in the case of Polypterus palmas through to almost one metre (about 36 inches) in the case of Polypterus endlicheri congicus.

Bichirs are very distinctive. They have long, thin bodies, like an eel, but with heavy armour plating similar to that seen on gars. Along the back is a series of a dozen or more small flag-like dorsal fins. The pectoral fins extend from muscular lobes, a bit like stubby arms, and bichirs will indeed prop themselves up on their pectoral fins when resting on the substrate. Their jaws are very simple and more like those of amphibians than bony fish. Internally they are just as unusual. They have paired lungs like those of lungfish, but they have a spiral valve at the end of the digestive tract more like those seen in sharks.

Ecology

All bichirs inhabit slow-moving and still water habitats, particularly shallow water areas thick with aquatic vegetation. They are predatory, taking a variety of prey including insect larvae, crustaceans, snails and small fish. Bichirs hunt primarily at night using their keen sense of smell. Bichirs are obligate air-breathers, and will periodically swim to surface to gulp air. This allows them to survive in swampy habitats where most other fish would die.

Water chemistry

Water chemistry is not normally an issue. All bichirs do well across a broad range of conditions, from pH 6 to 8, 5-20 degrees dH. Like all fish, stable water chemistry conditions in the aquarium are helpful. While the Ropefish sometimes occurs in slightly brackish water, this is not its prime habitat and it does best in purely freshwater conditions.

Aquarium size

Most of the bichirs offered for sale are relatively small fish, getting to between 30-40 cm (12-16 inches) in length. As such, they will do well in tanks from 180 to 250 litres (40-55 Imperial gallons) in volume. Water depth is not critical, but since these are obligate air breathers, the water shouldn't be so deep that very small specimens (such as juveniles) cannot easily get to the surface.

Bigger species like the Ornate Bichir Polypterus ornatipinnis (to 60 cm/24 inches). Such fish will obviously require larger aquaria to be kept successfully, from 350 l (77 Imperial gallons) upwards.

All bichirs are good "jumpers" and it is critically important that the aquarium has a tight-fitting hood. Ropefish are infamous for escaping from tanks, but the other bichir species will jump out of open-topped tanks as well.

Decoration and planting

Bichirs are nocturnal fish in the wild and prefer tanks without too much strong light. Once settled down, they usually become day active without problems, but this will be encouraged if the tank has plenty of caves and floating plants. Thickets of plants around the edges of the tank will also help. Choose sturdy plant species appropriate to the size of bichir being kept. For the smaller species, things like Indian Fern and Anubias would be suitable, while larger species would benefit from plant species such as Amazon swords, giant Vallisneria and large Java ferns.

Although it is not essential, the smaller bichirs especially like to dig, and soft silica sand could be used instead of gravel. When choosing rocks, look for species that are not likely to scratch their bodies. These are clumsy fish, and when alarmed, are prone to damaging themselves on sharp rocks.

Diet

Bichirs are mostly carnivorous, though analysis of the gut contents of wild fish reveals they do consume some plant material including seeds. They are opportunistic, and the range of prey varies from insect larvae through to frogs.

In captivity they eat all sorts of things, with chopped seafood and lancefish being ideal staples for the big species, and wet-frozen insect larvae and crustaceans suitable foods for the smaller species. They enjoy live foods, and earthworms and river shrimps make good treats. But since they hunt by smell rather than sight, they don't need live foods, and they certainly don't need to be fed feeder fish or similar expensive (and potentially risky) foods.

As with all carnivorous foods care should be taken to avoid overfeeding, and thiaminase-rich foods like prawns and mussels must be used in moderation to avoid problems with vitamin B1 deficiency.

Social behaviour

Most bichirs appear to be solitary fish that do not normally form schools. They are mildly to very territorial, depending on the species. In general they are best kept singly, though the smaller species can be kept in groups of three or more, if given enough space. Bichirs mix quite well with robust community fish including medium to large characins, catfish, loaches and non-aggressive cichlids.

Ropefish are different, and seem to be gregarious in captivity. Keep them in groups of at least three specimens. They mix well with all sorts of community fish including Corydoras, gouramis and angelfish. Note that very small tankmates will be eaten, including neons, guppies and cherry shrimps.

Bichirs and ropefish should never be kept with anything nippy or aggressive; they move too slowly to avoid trouble, and their fins are easy targets for fin-nipping species. Puffers, tiger barbs and serpae tetras would make very poor tankmates. Cichlids can be aggressive towards bichirs, and should be chosen with care. Most Central American and Rift Valley cichlids are far too aggressive, but depending on the size of the bichir, things like kribs, acara, oscars and eartheaters generally work well.

Sexing and breeding

Males and female bichirs can be told apart by the shape of the anal fin: at sexual maturity the anal fin of the male becomes much larger, and is apparently used to stimulate the female to release her eggs during spawning. Females are believed to be a bit bigger than the males, and very likely become swollen with eggs when ready to spawn. Male bichirs initiate spawning by chasing females and bumping her with his head. In some cases at least, the males jump out of the water. This goes on for a day or two, the female releasing small batches of 5-10 eggs at a time. Bichirs appear to produce total spawns of a few hundred eggs.

Reports of successful breeding of bichirs in home aquaria are very rare. One of the few occasions where bichirs have been spawned in a home aquarium is described by Igarashi in 'Jurassic Fishes', an essential read for anyone wishing to breed these fish. His pair of Polypterus senegalus scattered their eggs among benthic plants. The sticky eggs hatch within 60 hours and the fry become mobile within the next 24 hours. The fry need tiny live foods at first, such as brine shrimp nauplii, but bichir fry are not good at catching food and the aquarist will need to provide food in large quantities to have any degree of success. Newly hatched bichir fry are delicate and sensitive to poor water quality. Two weeks from hatching the fry are much more mobile and feed more vigorously on small crustaceans and insect larvae. At the same time the young bichirs become more aggressive towards one another, and fighting between them can dramatically increase mortality.

Young bichirs are notable for having external gills, like a tadpole. These external gills persist for several months, and sometimes very small bichirs are sold in aquarium shops that still have these gills in place. Over time the gills atrophy and eventually disappear completely. In the case of Polypterus senegalus, specimens up to 10 cm long may still bear external gills.

Species

The standard species of the trade is the Senegal, Grey or Cuvier's Bichir (Polypterus senegalus). This species gets to about 35 cm (14 inches) in length and has a very wide distribution across Africa, from Gambia on the west to Egypt in the east, and as far south as Zambia. It is absent only from North Africa and the Sahara, the Rift Valley lakes, and the region around South Africa. It is normally greyish-green in colour, though an albino form is also available.

The Senegal Bichir is an excellent and highly regarded aquarium fish. It is extremely hardy and adaptable, and by bichir standards, neither aggressive nor particularly predatory. Like all bichirs individuals tend to be snappy towards one another, but not excessively so, and groups of three or more can be maintained in sufficiently large tanks. Wild fish feed principally on insects as well as other small prey (frogs, fish, crustaceans and snails). Aquarium specimens do well on wet-frozen foods of all types. They also enjoy earthworms. Although they will eat very small tankmates, they otherwise mix well with community fish, and are often kept in community tanks with an African theme, alongside species such as Congo tetras, Ctenopoma, butterflyfish, and kribs.

The Marbled or Shortfin Bichir (Polypterus palmas) is another popular species. It is similar in size and shape to the Senegal Bichir. Adults are around 30 cm (12 inches) in length when mature, and have a mottled grey colouration with numerous light and dark speckles. There are in fact three subspecies of Marbled Bichir: Polypterus palmas buettikoferi, Polypterus palmas palmas, and Polypterus palmas polli. The trade usually sells them all as Polypterus palmas, but some retailers may make a point of offering one particular subspecies. Polypterus palmas polli is probably the most commonly traded subspecies. In terms of care, all three Polypterus palmas species are identical.

The Ornate Bichir (Polypterus ornatipinnis) is the most commonly traded of the big bichirs. Maximum length for this species is around 60 cm (24 inches). This species is noted for its fine colouration: the body is essentially black with thousands of bright white to golden yellow spots, the belly is off-white, and the fins are coloured in a similar way to the body. The Ornate Bichir is very territorial towards its own kind, and its sheer size mean that maintaining groups is probably impossible outside of a public aquarium. It does get along quite well with larger, but non-aggressive, tankmates such as catfish, giant gouramis and big characins.

The other big bichir seen regularly is the Saddled Bichir (Polypterus endlicheri). This fish gets to about 60 cm (24 inches) under aquarium conditions, though wild fish may get better. It has a more flattened head than most bichirs, and a very distinctive colouration. Its body is speckled greenish-grey to light brown with a series of dark saddle-like bars across the dorsal surface. There are at least two subspecies, Polypterus endlicheri endlicheri and Polypterus endlicheri congicus. Of the two, Polypterus endlicheri congicus has much weaker markings but apparently gets much bigger in the wild, reportedly up to 97 cm (38 inches).

The Ropefish (Erpetoichthys calabaricus) is a highly distinctive fish from the Niger Delta. It is very long and thin, and unlike proper bichirs, it lacks pectoral fins. Its dorsal fins are very small, as are its pectoral fins. Mostly it slithers across the bottom of the tank, but it can side wind through the water extremely rapidly when alarmed. Aquarium specimens get to about 40 cm (16 inches) in length. They are green in colour with orangey bellies. Ropefish are gregarious and peaceful, and shouldn't be kept with bichirs, which tend to be more aggressive. They are good community fish, provided their tankmates aren't too small. However, they are notoriously good at escaping from aquaria, and some thought should be taken to ensure that any small holes in the hood are carefully plugged, for example with duct tape.