About Polypterus, demands on tank size and setup
The fish belonging to the Polypterus species are often known as Dinosaur fish as they have evolved very little compared to most of the other species. They also have the common name of Swamp Dragons as they do resemble these creatures with their long sleek bodies and wing like finnage.
At one time many people confused these creatures with eels but they are in no way related, they are a species in their own right. They have their own distinctive features that keep them separate from other fish species and it is these features that often attract keepers to have a go at caring for a specimen. They have a serrated dorsal fin, wide eyes and nostrils that are raised, most of the species also have teeth that are always visible, not the sort of fish you would wish to add to the average community tank.
If you do wish to have a go at keeping one of these fish it is best to try to replicate their natural surroundings as much as possible. Polypterus originate from Africa and India where they inhabit very slow moving waterways that are heavy in vegetation. They love to inhabit murky water as they use this to their advantage when hunting for unsuspecting prey. Their eyesight is very poor so they rely on their keen sense of smell when looking for food, hence their large protruding nostrils. Their bodies are covered with large thick scales offering them excellent protection and also from injuring themselves as they move through their chosen waterways.
These fish grow large!
Up to 30 cm so they must be kept in a large aquarium, often they are sold as juveniles without the prospective owners realising this, smaller specimens can be kept in smaller aquariums but always be ready to upgrade to a larger tank as they grow and mature.
Another distinguishing feature of these fish is the fact that their swim bladders has also developed into a primitive lung, they can breathe out of the water for quite a length of time, this helps them as in the wild they will cross dry land when they are searching for a better location to occupy especially when the onset of a drought occurs and they need to move home to survive. Their bodies must stay moist though, if it starts to dry out them the fish will usually be doomed and can carry on no further.
Setting up a Polypterus Tank
The Polypterus species are quite hardy, this is probably due to the native specimens having evolved to cope with some hard conditions in their natural habitat, this has been passed down the generations but like all fish species they do still require to be kept in aquariums that meet their needs and they still deserve to be kept in the highest water quality possible.
One of the main criteria to consider when selecting an aquarium for Polypterus is their potential adult size, some of the larger species can grow up to 24 inches and need a lot of swimming space, the footprint of the aquarium has to be large enough to allow for this. Using a shallower tank with a larger footprint will make more efficient use of the water volume that the tank contains as they will spend most of their time at the bottom levels anyway. The smallest tank I would recommend is a tank that is 6 foot in length and 2 foot from back to front, some of the smaller species may be fine with a tank that is four foot in length but never any smaller. The fish will need access to the water surface, they are labyrinth fish and will need to gulp the air occasionally, always leave a gap between the water surface and the top of the tank. As mentioned earlier, they are excellent jumpers and escape artists so the use of a tight fitting lid is a must, never keep these in an open topped tank or you will find them on the floor the next morning.
You can keep more than one specimen in the tank as long as the tank is large enough to allow them all swimming space, you may witness the odd squabble but these are more of a show and any physical damage is rarely done. As usual there are exceptions to the rules as there are with all fish species so an over aggressive specimen should be re-housed and kept as a single specimen in a separate tank. All specimens should be of a similar size when introduced to the tank and there should be no recurring problems.
They feed from the substrate so to make life easier for them it is best to use a thin layer of aquarium sand, this will help them locate the food better plus it has the added bonus of being easier to keep clean.
Hiding places will be needed to be added to the tank, this can either take the form of simple rock formations, piles of bogwood or even lengths of pvc tubing that has a large enough diameter so that the fish can swim into them easily. Adding the hiding places will make the Polypterus feel more secure as they know they can retreat into such places if they need to.
If you are looking to adding live plants to the tank it can be hit and miss, these fish do not eat the plants but they can dislodge then if planted in the substrate. To overcome this problem you can attach tuber plants such as Anubias to the bogwood or other décor, Java Fern can also be used and this way the plants should be undisturbed.
If you are happy to use artificial plants then that is fine, even if they are dislodged it only takes a few minutes to replace them or just let the fish place them where it suits them.
As the diet of this fish is mostly protein based and they are messy eaters, the filtration needs to be well up to standard. For the tank size required it is often better to use two external filters, one mounted at each end so that you know the water quality will remain high. If using a heater inside the aquarium always cover the element with a suitable heater guard, these fish are active and the last thing you want to happen is for the fish to burn themselves, heater guards do not cost a lot of money but are well worth it if it saves fish getting injured.
The water temperature should range from 25-28°C (77-82°F), they do prefer to be at the higher end of this range but definitely not outside these parameters. The pH is fine if it floats around the neutral mark, preferably slightly acidic and the hardness should be slightly hard as well.
Subdued lighting is more suited to these fish, their eyesight is poor anyway so the lighting level is not critical for them but bear in mind which plants you have added to the tank if any as they will require the appropriate levels.
When first adding the Polypterus to the tank always observe them carefully for the first couple of weeks, they are resistant to most diseases but if they are purchased from wild stock they may carry some parasites or leeches, they will flick against décor to try to remove them if this is the case. A Formalin bath in a treatment tank will eradicate the leeches and parasites very effectively.
To keep the water quality high it is very important to back up the filtration with regular water changes, at least 10% weekly, you may need to do larger water changes if the nitrates etc. are not stable. As you can see from this article keeping the Polypterus is not difficult but as with all fish they still require care and attention but in return will give you many years of pleasure.