Polypterus in general
“if I had discovered only this species in Egypt, it would compensate me for the pains usually involved in a long journey”. According to scientist Geoffry Saint Hilaire, who in 1798 took part in a scientific expedition organized by Napoleon to the mysterious and closed Egypt.
Sitting along the Nile, he discovered a meter-long primeval fish, which was already known to the Egyptians from the time of the Pharaohs. The locals called the fish something like Bee-sheer, which the French may have phonetically spelled Bichir in their own way. In 1902 the species was given the scientific name Polypterus bichir. The find was of great scientific significance.
Today’s primeval fish Polypteridae are the only survivors of the group Polypteriformes. Its origins go back to the late Cretaceous period, from 100-60 million years ago, known as the last phase in which dinosaurs flourished. Polypteriformes occurred in the area that now includes Africa and South America.
Today’s Polypteridae (Bichirs) are among the most primitive ray-finned species still in existence. They all occur in freshwater areas in Africa, most of them up to about 10 degrees north and 10 degrees south of the equator. A fossil find of the modern Polypteridae in Chaad indicates that the species as we know it today already existed in the late Miocene (5.3 million years ago). The fossil (appropriately named Polypterus faraou) bears close resemblance to Polypterus bichir and Polypterus endlicheri, two species still found there.
Evolution does not seem to take place very quickly in these primeval fish. Nevertheless, due to the large geographical spread and different habitats, various species and variants have arisen: The family itself consists of two genera
- Erpetochthys (met maar één soort: Erpetochthys calabaricus)
- Polypterus. Polypterus consists of 13 species and a number of variants within them.
In recent decades, much confusion has arisen among ichthyologists about the species classification and how the later discovered variants should fit into it. Substantial changes have recently been made to the species classification due to a change in insight. A distinction is now made into three main groups of Polypterus:
- The Senegalus group including Erpetoichthys. These upper jaw types have a longer upper jaw than the lower jaw or at least of equal length. The mouth opens downwards so that they are better equipped to eat (dead) food lying on the bottom. The upper jaw group consists of E. calabaricus, P. senegalus, P. palmas, P. delhezi, and P. polli.
- The Weeksii group. Also an upper jaw type with a longer or minimally equal upper jaw than the lower jaw. This group includes P. weeksii, P. ornatipinnis, P. retropinnis, P. teugelsi and P. mokelembembe
- The Bichir and Endlicheri group with a lower jaw longer than the upper jaw, so that the mouth opens upwards. This makes them more specialized in hunting live animals, such as amphibians, aquatic insects, and fish. This group includes P. bichir, P. ansorgii and P. endlicheri. Lower jaw types tend to be a lot larger than the upper jaw types.
Bichirs have a cylindrical elongated body, resembling that of a reptile. It is equipped with scale armor and 7 to 16 separate triangular dorsal fins (Polyperus means many-finned), which gives the fish a dragon-like appearance. The pectoral fins are exactly where you would expect the legs to be in a lizard. The swim bladder evolved into a primitive lung, which also allows the fish to use air from the surface. Combined with the gills, they can survive in the low-oxygen conditions of warm swamp areas and even out of the water for a while. Even if the oxygen content in the water is sufficient, they will regularly swim to the surface for a mouthful of air. Juveniles have clearly visible external gills, like salamanders. In most specimens, these disappear at a later age. The skin is covered with a strong scale armor. The scales are triangular, with a hook at the end, and covered with a hard and tough material that also prevents water loss outside the water.
Polypterus has poor eyesight and a highly developed sense of smell. It follows scent trails to find food. For this, they are equipped with tubular nasal openings. Polypterus can survive out of water for several hours, and in humid conditions for up to 2 days. The fish then propels itself over land with its pectoral fins.
Prey are slowly stalked largely by sense of smell and swallowed up close.
Males can be recognized by a thicker and more muscular anal fin. However, this sex difference can only be seen at 15-20 cm in length. A number of species are sexually mature after 2 years, in the larger species only after 6-8 years. Females generally grow larger than males.
Polypterus ansorgii – Guinea Bichir
Polypterus ansorgii is a lower jaw species that has long been seen as a smaller variant of Polypterus bichir. The only difference between Polypterus bichir and Polypterus ansorgii is that the latter has no racing stripes over its body, but has a military-like spotting pattern. Many sources (also on the internet) mention Polypterus ansorgii does not grow larger than 28 centimeters. This is not the case. With a maximum length of 90 centimeters, it is even one of the largest Bichirs.
Polypterus ansorgii has a small distribution area. The species is only found in a limited area within Guinea. Unconfirmed sources also report locations in Nigeria. Due to its small distribution area, this fish is a rarity in the aquarium. For specific enthusiasts, obtaining a Polypterus ansorgii is the ultimate. A lot of money is then paid for a copy.
Polypterus are non-aggressive ambush predators and opportunistic scavengers. They generally move cautiously and are partly hidden. They are often more active at dusk and at night. There are differences in the level of activity per species. For example, the lower jaw species (which often become larger) have less tendency to hide and move more actively. Variations with regard to agility, curiosity, and predatory behavior are not only found in the species but – – within a bandwidth – also per specimen. As a result, different aquarium keepers often have different experiences with a specific species.
Polypterus is peaceful towards other fish species, but it must be clear to them that they do not fit in their mouths. Smaller, especially more elongated fish up to 2/3 of their own size are at risk of being swallowed. The lower jaw types in particular can devour large prey: they are able to open their mouths almost the size of the diameter of their body.
They are also usually tolerant of conspecifics (provided they are of approximately the same size), although there are skirmishes. These rarely lead to injuries. However, there are experiences with individuals that cause constant unrest or even do not tolerate conspecifics.
The Polypterus is no match for aggressive co-inhabitants, such as breeding cichlids. Often they then hide and stop eating completely.
Polypterus’ eyesight is poor. The prey is slowly stalked by a combination of chance and sense of smell and swallowed up close. Prey is seldom actively pursued (this is only more common in the lower jaw types). Often it is hovered over or passed several times before the end of the olfactory trail and is recognized as bait or prey and the Polyterys strikes. This can give the viewer a sluggish, pathetic, and jovial impression, and the misplaced expectation that faster tankmates are safe. Appearances can be deceiving: The Polypterus can strike quickly and adequately from an ambush and is able to develop enormous speed with a slap of the tail. If that is not effective enough, there is always twilight or night to easily catch prey.
Polypteruses produce sound. A rhythmic beating sound can only be heard with equipment and occurs during encounters between conspecifics, where one of the animals spreads its dorsal fin and thereby produces the beating sound. Research showed that the sound was strongest in the frequency range between 100-200 Hz, with a maximum of 3 pulses per second. Volume decreases as fish move away from each other. Moans can be heard without the intervention of equipment when they are chased or when one specimen is chased away by another. It is still unknown how the sounds are produced mechanically. Despite being a rudimentary predatory fish, the dragon-like animal, with its funny pectoral fins and calm way of moving, gives the fish a touching and sympathetic appearance to many. Aquarium owners often build a pet bond with them, whereby the animals literally eat out of hand. In the aquarium, they can live up to 10-15 years.
It is common for Bichirs to float at the surface, preferably resting on water plants or a piece of wood. Some show this behavior frequently, other specimens do this especially when they are relatively new to the tank. Often a Bichir is bought that is very active in the store, and only floats on the surface in its own tank. It’s a natural defense position: when Polypteruses are small, they are most vulnerable to other predators when they have to go from the bottom to the surface at regular intervals to get oxygen. Because they can’t afford this dangerous trip, they instinctively look for a place near the surface. Younger specimens in particular spend most of their time on the surface. A decoration with plants on which to rest is recommended. Larger fish usually only exhibit this behavior if they are new to the tank or if they are uncomfortable with aggressive tankmates. In adults, the behavior occurs mainly in species from the upper jaw group.
Jumping forward uncontrollably
This behavior is a defensive response if it feels threatened in a startle response. It then seems passive and at rest, and suddenly suddenly shoots forward uncontrollably with a slap of the tail. This does not take into account obstacles in their way, so they can crash into anything. They have a sensitive lateral line system. The slamming of a door in the house or walking hard can be the trigger
Perching/balancing on tail
One of the most unique behavioral traits is tail balancing. With this they are slanted upwards and on the lookout in the water ready to strike if prey presents itself and comes too close
When the fish’s stomach is full, it bends its body from side to side, tightening its muscles to redistribute the food in the stomach. A bit like overloading a suitcase.
Similar to the behavior seen in crocodiles, Bichirs can also perform a death roll. They then bite into a large piece of bait and turn on their axis to tear a piece off. The behavior is not very common and will not be easily observed in the aquarium because most aquarists will not feed complete carcasses.
Breaking the surface
If a specimen breaks the surface (other then gulping air) then it is a sign of the start of the mating season
Bending the anal fin (only males)
The muscled anal fin is important for courtship. When the males become sexually mature, they instinctively show off by bending their anal fins. With the bent anal fin, they are able to catch eggs, fertilize them, and release them.
If a male is stalking a female then it is part of the courtship.
Polypterus can use their dorsal fins to scratch the sides of their body. Wile scratching they bend their muscled body so they can reach further.
Probably yawning is an exercise to keep the mandibular joints healthy and flexible or to reposition them after swallowing a meal.
Lay next to or upon each other
Especially in aquariums with too few hiding places or too bright light, it happens that Bichirs lie on top of each other in the corner. This is just an attempt to hide. They feel safe if they lie next to or under each other and can no longer see the rest of the environment
Bury their head
This behavior has only been observed in the P. Endlicheri, P. Delhezi, and P. Weeksii. It is used when they feel threatened, but also as a hunting technique. The head is buried in the sand in such a way that the eyes protrude. The markings of these species on the body also help camouflage the rest of the body in their habitat.
An aquarium with open spaces combined with a lot of shelter in the form of plants, rocks or wood. Slightly dimmed lighting makes them feel more comfortable and more active. Especially with young specimens or with larger specimens that are new, it is advisable to have places where they can rest close to the surface (plants or wood).
They are powerful, very muscular fish that like to hide and forage in vegetation, so it is advisable to secure plants well. Caves in which they can hide contribute to their well-being. The height of the waterline is not important, the bottom surface is. Younger fish can be kept in a smaller tank from 80 centimeters. Depending on the species, they grow quickly. They will soon need a very large tank. If several specimens are kept, provide several hiding places. Cover the aquarium tightly and check that the hood does not contain any crevices or openings: they are true escape artists, in fact, most specimens end up next to the aquarium for novice aquarists. With sufficient strength in the body, they are able to push cover plates and light hoods upwards. Furthermore, make sure they always have the option of drawing air from the surface.
Polypterus is a strong fish with a high resistance to fish diseases, such as Ich. Wild-caught specimens (most Polypteruses on the market) often suffer from the parasite Macrogyrodactylus polypteri, which can eventually kill them. They do not tolerate most medications against fish diseases well. It is recommended that the dosage of these drugs be limited to half or two-thirds of the recommended amount for them.
Since Polypterus can become tame in the aquarium, it is tempting to catch them by hand. Do not do this! The rear fins are razor sharp and a fleeing Bichir knows how to use them.
Polypteruses are not aggressive towards other fish species. Suitable cohabitants for Bichirs are fish that do not fit in the mouth and are not aggressive. For larger Polypteruses (P. endicherii , P. bichir, P. Ansorgii) the following co-inhabitants are suitable (not exhaustive):
- Other species of Bichir
Cichlids (avoid breeding pairs as they can cause too much aggression)
- Astronotus ocellatus
- Kronoheros umbrifer
- Tropheops tropheops
- Vieja maculicauda
- Thorichthys aureus
- Uaru amphiacanthoides
- Herichthys carpintis
- Copadichromis chrysonotus
- Protomelas annectens
- Thorichthys meeki
- Chromidotilapia guntheri
- Hemichromis lifalili
- Nimbochromis livingstonii
- Cyrtocara moorii
- Nilapia mariae
- Pimelodus blochii
- Hemibagrus wyckii
- Brachyplatystoma juruense
- Hemisorubim platyrhynchos
- Auchenoglanis occidentalis
- Parauchenoglanis macrostoma
- Datnioides pulcher
- Datnioides undecimradiatus 16”
- Lepisosteus ocula
- Atractosteus tropicus
- Lepisosteus platostomus
- Xenomystus nigri
- Gymnotus carapo
- Macrognathus aculeatus
- Gymnothorax polyuranodon
- Echidna rhodochilus
- Apteronotus albifrons
- Gnathonemus petersii
- Potamotrygon leopoldi
- Potamotrygon motoro
- Metynnis argenteus
- Hepsetus odoe
- Ctenolucius hujeta
- Distichodus notospilus
- Distichodus fasciolatus
- Brycinus nurse
- Hydrocynus goliath
- Hydrolycus scomberoides
Do not keep them with aggressive fish species, such as territorial cichlids, snakeheads (Channa), and fish species from the Labeo family. They are not resistant to aggression. Also the combination with catfish with a suction cup (for example Plecostomus) often does not work as the catfish likes to graze and destroy the armor of the Bichir.
Polypterus ansorgii is a carnivore. In their habitat, Polypterus mainly eat small fish, insect larvae, crabs and shrimp, and amphibians. They are non-aggressive predators, but also opportunistic scavengers.
The under jaw species are more adapted to catching live, free-swimming prey. The upper jaw species generally live more on carrion and benthic animals. However, there are a number of exceptions to this rule. A number of upper jaw species seem more adapted to the life of benthic animals and carrion, but show more hunting behavior than the lower jaw species.
Polypterus is not a picky eater. Suitable food (live and frozen) are:
- Mosquito larvae
- Pieces of beefsteak
- Fish meat (avoid salmon because of its high concentration of oil
- Meal worms (avoid popped ones, since they can cause constipation)
- Feeder fish (avoid goldfish because of the high concentration of copper, fat and hormones)
- Dried pallets
Variation in the menu is important for good health.
Breeding Polypterus ansorgii
As far as is known, Polypterus ansorgii has never been bred in captivity.
However, breeding is expected to proceed in a similar way to other Polypterus species.
Breeding of Polypterus in general
The most difficult thing is to initiate the mating. In nature, mating is usually initiated by periodic disturbances, such as the onset of the rainy season. It is assumed that changes in temperature, water composition and air pressure create an impulse. On breeding farms, mating is often forced with hormones. An even more animal-unfriendly method is the addition of 1 drop of sodium iodide (KJ) 1% solution per 100 liters of water. Under no circumstances more! It is also mentioned that the aquarium must then be well covered because the solution makes them restless.
Mating behavior can often be observed after a regular water change. To mimic natural conditions, they are kept at a (dry season) temperature of 28-30 degrees Celsius with a PH of 6.0. To stimulate the rainy season, we lower the temperature to 16-21 degrees Celsius and a PH of 7. Then we add a little softer distilled water and let the temperature rise again to 26-28 degrees Celsius. This should start the mating process in many cases, provided all parties are ready for it, of course. Other sources also report the successful addition of some sea salt with trace elements.
Mating begins as the male repeatedly breaks the surface, arches the body, displays his spread fins, and slowly descends toward the female. Coming from behind, the male makes contact with her with a number of subtle headbutts. The female remains motionless as the male stimulates the oviduct of the female with his anal fin, collects the approximately 300-1000 released eggs, fertilizes them, and releases them again. This process repeats for several days. The parents show no brood care. The eggs hatch after 4 days (at a water temperature of 26 degrees Celsius), after which the fry switch to free swimming after another 3 to 4 days.
To breed them, several tanks are needed: one for mating and one for incubation. Mating requires a soft sandy substrate and several low, fine-leaved plants such as Java Moss. This is where the eggs (hopefully) will be laid. The other tank is needed for the brood to hatch and grow up. No substrate is needed here. When the mating is completed, move the plants with the eggs to the breeding tank (27-28 degrees Celsius and pH between 6.5 and 7) as soon as possible.
Within 60-90 hours the eggs hatch. During the first 6-7 days the fry live off their yolk sac and remain attached to the plants. Then they switch to free swimming and should be fed with chopped mosquito larvae and baby brine shrimp. In this phase, the number of young will unfortunately be reduced due to fighting and cannibalism.
Patrick de Pijper
Bijgewerkt op 31 August 2023 door John