A further step in Polypterus keeping: dealing with Polypterus ornatipinnis

A further step in Polypterus keeping: dealing with Polypterus ornatipinnis

Written by Francesco Zezza Monday, 21 March 2011 00:00

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Polypterus ornatipinnis is quite rare and pricey. However not a lot of aquarists consider offering these fish a home. I decided to buy one following the positive experience I had with them in the past. Luckily the price of the fish proved reasonable. There was only one individual available on the list of one of the LFS I keep in touch with. The fish was described as being 25 cm TL (roughly the size of my previous one); on arrival it turned out that it was closer to 40 cm, which was a nice surprise indeed.

The family Polypteridae belongs to the Actinopterigians group. This group, also known as “bony fishes”, includes most of the fish currently in existance and is divided into two genera:

• Erpetoichthys (Calamoichthys) calabaricus (single species genus). The fish has a long snake like body; small fishes are commonly known as “rope fish” and
  
• Polypterus, holding about ten different species plus many sub-species which on occasions are quite different to each other. Polypterus ornatipinnis is a member of this genus. The size of these fish, to the best of my knowledge, spreads from quite small (P. ansorgii) to considerably large (for instance the “monster-like” fishes of 90 cm and more such as P. endlicheri congicus). There are three known species of Polypterus senegalus: Polypterus senegalus, Polypterus senegalus senegalus andPolypterus senegalus meridionalis while the actual existence of a fourth species (possibly from the Nile river area) is debated.

The taxonomy of Polypterus ornatipinnis is as follows:

• Phylum: Cordata
• Subphylum: Vertebrates
• Class: Actinopterigians
• Order: Polypteriformes
• Family: Polypteridae
• Genus: Polypterus
• Species: Polypterus ornatipinnis (Boulenger 1902).

As with all Polypterus P. ornatipinnis is rather peculiar in shape: an “eel like” body with a single lobe tail showing (in this case having a striking black and yellow coloration), with almost “bony” scales and a dorsal fin divided in many “finlets” (nine to eleven). All finlets can be hidden in a sac on the back of the fish; this feature allows the fish to swim backwards out of extremely tight holes and crevices thus avoiding the danger of being trapped when hunting or hiding.

Similarly the pectoral fins of this fish resemble a human hand. The shape and structure of these allow Polypterus to move on the ground from one body of water to another. The radical adaptation of these fishes to changes in their environment has also resulted in them acquiring a peculiar breathing apparatus consisting of two asymmetrical lungs, the bigger of which stretches up to the fish's anal region.

Naturally Polypterus also have gills and thus can normally breathe under water as with all fish. There is some debate amongst fish keepers regarding the need of polypterus to breathe fresh air; some argue that tank kept fish are in danger of drowning if not allowed to reach the surface to breathe air. I can neither confirm nor refute this statement as, to stay on the safe side, I allowed my fish an easy access to the surface and I noticed it, many times, coming up “gulping air”.

Further to the physical characteristics of Polypterus ornatipinnis indicated I should add that the fish has two short sense receptors allowing it to smell/recognize its prey when hunting, the way these fascinating fishes do, in absolute darkness.

In the wild this fish lives in the Congo river Basin and, oddly enough since they are quite far and away, in the Lake Tanganyika.  It appears that Polypterus can easily adapt to a variety of environments: P. ornatipinnis has been found in extremely alkaline environments (e.g. in the Rift Valley) as well as in the Congo River, which flows among the forests of western Africa. In general  the fish prefer still, particularly turbid, waters with a lot of floating silt or else an extremely moderate flow in shallow or very shallow bodies of water with lots of hiding spots (e.g. fallen branches). Polypterus are ambush predators and feed almost only at night on everything “edible” they happen to meet. They are said to be rather territorial even if not to the extend that some cichlids are.

The information above points at the way this fish should best be kept in captivity. I would add a couple of notes on this front:

Though water chemistry and strong filtration are not of extreme importance when keeping these fish it is important to pay attention to the aquascaping of the tank:

• provide the fish with dim lighting, a soft substrate in a well planted (if possible) tank. Make sure there are lots of shelters and crevices available to it; using round stones and large roots or bogwood ensures that the fish will not be in danger of hurting itself by swimming on sharp edges.
• polypterus are “masters of escape”, so make sure your tank is securely closed from all sides.
• polypterus are curious beyond the imaginable; a 'dark hole' is something they cannot resist. Protect wisely any kind of techie stuff placed in the tank as they are bound to explore. As a result they can get trapped (despite their ability to swim backwards); if that happens freeing them will not be easy.

Provided the points above are taken into account and the size of the tank is appropriate a community of Polypterus can be kept together without stress or fights. Sooner or later the fish will begin to swim around even under bright light - all the more so if encouraged by a few tasty morsels.

In the wild Polypterus ornatipinnis attains a TL of about 60 cm (perhaps more). Previous experience has taught me to be careful about the chosen tankmates for this fish.  More specifically I have previously hosted my specimen in my 500 liters Malawi tank; the fish carefully cleared off all the fry, both M'buna and haps, he encountered. I thought some would survive but I underestimated the size of its mouth. In the end I found myself in the not so pleasant position of having to deal with an unexpectedly large fish.

Careful planning is required to ensure the fish feed properly. The easiest way to achieve this is to place Polypterus in a dedicated tank. All Polypterus are slow feeders and mainly carnivores; all Malawians are messy and gluttonous feeders. If Polypterus is to be kept with M’buna the vegetal preferences of the latter should also be taken into account.

Like all nocturnal fish when they sense food with their receptors a slow, somewhat random, search begins; this search ends once Polypterus get to their target (the food). The fish are quite good at locating food in a dark tank though their search can take a long time. As a result, if they are kept with fast, eager feeders, there is always the danger that they will go without food  way too often as their tankmates will eat the food before Polypterus manage to get to it. In such cases the aquarist should consider introducing one more feeding session during lights out. If that happens make sure that the lights of the room are also out - not just the lights of the tank (all fish are awake when the room in which the tank is located is properly lit).

The fish should be kept mainly on a carnivore fresh or frozen diet. Dry food can be offered if need be; it will be accepted, though Polypterus do not actually like it. Yet, from a fish keeper's point of view dry food is rather convenient to be completely eradicated from a fish's diet. The key point is that dry food should be the exception rather than the rule.

So let's see what happened when I introduced the new fish to my tanks:

My son, Leonardo, impressed by the size of the fish on its arrival, nicknamed him “Dino” (short for Dinosaur) without considering the sex of the fish (in Italy Dino is a male personal name).

Considering the fish was coming from an LFS I trust and taking into account its size I decided to place it directly in my main tank. This tank has a capacity of 500 lit (125 US gals) tank and is serviced by two large external canister filters. The tank is not heated; it is aquascaped with small gravel, some round stones and a few plants, in particular Microsorium pteropus (Java fern).  As soon as I placed the fish in the tank it disappeared among the rocks and remained hidden for quite a while.

A few days later the tank begun to look somewhat empty (underpopulated); I started watching it until, one day, I found a half eaten fish (a Copadichromis sub adult) floating in the tank. Things started becoming clearer ...

Feeding the Polypterus and the Malawians in the same tank was not easy due to their different feeding habits. However, with a bit of careful planning I managed to cope without particular issues. I found  it quite useful to slightly overfeed, just to be on the safe side. As time went by the Polypterus gained in size. At the same time the “live food” in the tank that would fit his mouth finished and this (unhappy) event gave me the opportunity to re-introduce the intended diet:

Having kept the fish for a few months now the similarities in behaviour between Polypterus ornatipinnis and Polypterus senegalus are quite substantial. When the fish is half hidden it has a beautiful natural colouration. Its breathing is quite relaxed and its behaviour quite normal. All in all, it displays high levels of well being without any signs of stress.  Yet if one of us enters the room where the tank is located the result is always, invariably, the same: the fish rushes quickly toward the back (the darker part of the tank) making a quick exit from the open area. Things are slightly different when food is served; the Polypterus remains in the front of the tank though it is attitude towards is cautious, to say the least.

My efforts to encourage this fish to start interacting with us - or at least not to be so cautious of our presence -  has still not come to fruition. Though the fish is doing quite well it is still unaccustomed to members of our family. When we are in the room the fish takes cover among the stones and it quickly returns there when we enter the room - if, at the time, it happens to be out in the open.  Admittedly this is a bit disappointing. Nevertheless if that is what its nature dictates I am content to let my Polypterus live accordingly.

As was the case with my P. senegalus I am a bit concerned about the size of the morsels of food I have to offer. As the fish grows up the size of the food I must offer it gets bigger and bigger. This can potentially cause problems if the food remains uneaten. Thankfully up to now there have not been any food left overs in the tank. Naturally I am also concerned about the tankmates of this fish - I expect that as he grows the size of its mouth will also grow, which will make the rest of my fish 'suitable' to become snacks.

My final observation is that during mealtimes this fish has a somewhat funny habit: it occasionally grabs a large piece of chopped fish and hurries back to its shelter to eat it in safety.

If you plan to keep a Polypterus ornatipinnis it is worth reading the volume pictured below; to the best of my knowledge it is the only book available at hobbyist level. I would like to thank NeoGea for supplying me with one of the fisrt available copies of this book in Italy. 

My closing remark, having kept this fish for a while now is that I consider the experience highly rewarding despite the difficulties faced. A prowler, a demanding fish which many people consider to be a “silent killer” (my Polypterus indeeed meticulously cleared the tank of all its tankmates that could fit in its mouth but that could have been avoided if I had placed him in a dedicated tank)  this fish is also, for sure, a really interesting and gorgeous fish.

 

Photos by the author.

 

 

 

 

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