Keeping Polypterus senegalus
Keeping Polypterus senegalus
Written by Wednesday, 24 December 2008 00:00
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How I got him: Simply by means of the usual “fish-swapping” (I got him from a friend) at the year meeting of AIC (Associazione Italiana Ciclidofili) where – nowadays – are handled (switched, bartered, sold) also the so-called “unusual” fishes. Keeping one of these fishes, commonly known as “living fossils” has been one of my goals for a long time. Because of the usual “lack of room” in my tanks I picked a single specimen and, among the five available, the smaller one (supposed to be a female). The agreement was to return the fish to the actual owner once fully grown and my experience, in growing him, was supposed to be over.
A quick description: The family Polypteridae belongs to the Actinopterigian group (called “bony fishes” including the biggest part of living fishes) and is divided into two genera: Erpetoichthys (Calamoichthys) calabaricus (single species genus), with a long “snake like” body with small fishes commonly known as “rope fish” and Polypterus, with about ten different species plus many sub-species sometimes quite different from each other. To this latter group belongs Polypterus senegalus.
The size of Polypterus spreads from smaller individuals like P. ansorgii up to “monster-like” fishes of 90 cm and more (P. endlicheri congicus).
The taxonomic description of Polypterus senegalus is as follows:
- Phylum: Cordata
- Subphylum: Vertebrates
- Class: Actinopterygians
- Order: Polypteriformes
- Family: Polypteridae
- Genus: Polypterus
- Species: Polypterus senegalus
The shape (and biology) of all Polypterus is absolutely peculiar: an “eel like” body with single lobe tail. Polypetrus are covered, along their body, with almost “bony” scales and carry a long, odd, dorsal fin divided in many “finlets”, whose number vary according to the species. All the “finlets” can be hidden in a sort of bag on the back. This physical feature allows the fish to exit from extremely tight holes and crevices he has entered swimming backwards – say while hunting - without being locked in.
Similarly the pectoral fins of the fish are really odd. They resemble a hand – including carpal bones, to say so – and showing an astonishing ability in movement under extremely different circumstances. It is argued that these oddly shaped fins allow the fish to move on the ground from one body of water to another. The adaptation of these fishes to environments goes on with the, once more, peculiar breathing apparatus showing two asymmetrical lungs with the bigger one stretching all the way to the anal region. In addition to the lungs all Polypterus have gills fit to breath the way fish do. Some argue that when kept in a tank there is a risk of the fish drowning if not allowed to reach the surface and get air. I can neither confirm nor refute this statement as I kept my specimen in a tank which allowed it an easy access to water surface should the fish need air.
The fish is also equipped with two short sensor receptors allowing it to smell and recognize the prey when hunting – the way these fascinating fishes do – in absolute darkness.
Habitat: The genus currently contains three (sub)species: Polypterus senegalus, Polypterus senegalus senegalus and Polypterus senegalus meridionalis; the actual existence of a fourth species is debated. This seems to come from Nile basins and has not, yet, been scientifically described.
All Polypterus are used to live in extremely varied environments (in this regard P. senegalus is the undisputed champ populating the huge area that stretches from the Nile basin to sub-Saharan Africa) thus dealing with extremely variable water parameters including chemistry, temperature and so on. All the same some common characteristics of the biotopes they live in can be identified: our friend prefers still waters or, else, an extremely moderate flow, in water bodies which are shallow/absolutely shallow with lots of hiding spots (e.g. fallen branches or trees). Most likely the water will be of extreme turbidity with lots of floating silt. All Polypterus are ambush predators and eat almost only at night everything which is edible and can fit their mouths. They are also said to be rather territorial even if not to the extent a “cichlidiot” knows pretty well.
How can such an environment be replicated in a tank? Knowing that water chemistry is not the top priority we can go for dim lighting, soft substrate, well planted tank (if possible floating plants should be considered). Round stones (beware of sharp edges) and roots, preferrably bogwood, will provide caves and crevices for the fish to hide into. If properly furnished a number of fish can be successfully kept in such a tank, provided its size is appropriate. In time the fish will feel confident enough to swim around even during lights on; a tasty morsel should help to encourage this behaviour.
When keeping Polypterus it is important to remember the following:
- Polypterus are “masters of escape”, so make sure that the tanks are covered safely.
- Polypterus are curious beyond imagination; a “dark hole” is something they can hardly resist. Use proper “shields” for all water holes (eg filter intakes). If the fish try to explore such holes they may get trapped; freeing them will not be easy.
Set-up and management of the tank: in the wild Polypterus senegalus attains a T.L of about 50 cm hence in a tank it should remain smaller; this means that huge tanks are not required but do not go towards the other extreme either. For a single specimen or even a pair a 150 litres unit (correctly aquascaped) is enough. Lots of water changes and good filtration are a must. It is important to remember that all Polypterus tolerate high nitrate/phosphates levels; on the other hand they are very susceptible to bacterial infections. With regards to water temperature it is believed that a certain period of low temperatures (up to a few months) will help these fishes to thrive. Low temperatures slow down the metabolism (mostly when water goes below 22°C) and this, in turn, results in lower than usual food requirements. It is believed that the lower temperature period is one of the spawning triggers for this fish; I can neither confirm nor question this statement as I only keep one specimen. However it appears logical to me. Having said that I would recommend skipping the 'cold' period when dealing with very young, freshly imported or recently ill fish. As with swamp turtles, the fish may not be strong enough to deal with the low temperatures and may eventually pass away.
Feeding: all Polypterus are slow feeders. As nocturnal fish when they smell food (using the aforementioned receptors), they begin a slow (somewhat random) search which will eventually lead them to the food. This search can be rather long so if the fish is kept with eager feeders there is the actual risk that by the time they manage to get to the food there will be no food left for them. This is one of the main reasons for suggesting the use of a dedicated tank for these fish; alternatively the keeper must be very careful when considering possible tankmates. The chance to offer food during lights off could be considered; in this case it is important to make sure that there is no ambient light (eg from the room) lighting the tank.
If you offer live food (feeder fish) Polypterus will move slowly towards its target and in the very last moments it will attack its prey fast. This will take place during lights off or when the tank is dimly lit; at the time the other fish in the tank will have started to settle for the night. A Polypterus will hunt at the bottom, mid-water and (rather unusually) at the surface. Considering the shape and size of its mouth too big morsels are better avoided in order to facilitate eating and digestion easier. I will discuss this topic further down in more detail, when I present my experience from feeding my … “big snake”.
Dry food can be offered – as a last resource - when everything else is missing and will be, all in all, accepted. They do not like it, but dry food is from a fish keepers point of view way more convenient. Having said that dry food should be the exception rather than the rule.
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