Gymnarchus niloticus

Aba Aba

Classification

Gymnarchidae

Distribution

Has a huge natural range, being present throughout much of the northern half of Africa. It’s been recorded in Egypt, Sudan, Kenya, Chad, Cameroon, Nigeria, Niger, Senegal, Benin, Ghana, Sierra Leone, Gambia and Mauritania. Given this somewhat patchy distribution, it is likely that it is present in other countries as well, or has been misidentified on several occasions. The latter theory would seem unlikely given the unique appearance of the species though.

Habitat

It inhabits slow-moving streams and densely vegetated swamps and marshes.

Maximum Standard Length

66″ (165cm). Captive specimens of over 48″ (120cm) are virtually unheard of.

Aquarium SizeTop ↑

Speaking hypothetically, a truly huge aquarium would be required to house a fully grown adult fish, something in the region of 144″ x 48″ x 72″ (360cm x 120cm x 120cm) – 8155 litres would be just about acceptable. Although juveniles can be kept in smaller tanks they grow very quickly when fed correctly. It’s best left to public aquaria or the tiny minority of hobbyists with the facilities to house such a beast.

Maintenance

Prefers a dimly lit tank with areas of dense planting, large pieces of driftwood and twisted roots for cover. Any decor must obviously be weighted down securely. Powerful and efficient external filtration is also a must, although any water movement should be kept to a minimum. A sump–type filter is by far the best option, as the fish tends to be very destructive towards any equipment contained within the tank such as heaters and the like.

Water Conditions

Temperature: 73-82°F (23-28°C)

pH: 6.5-8.0

Hardness: 10-25°H

Diet

G. niloticus is carnivorous, and in nature feeds primarily on other fish and aquatic invertebrates. Captive specimens readily accept most meaty live and frozen fare, such as fish fillets, prawns, mussels and earthworms. There is no need to feed live fish or mammal meat such as beef heart. The latter in particular is actually detrimental to the long term health of the fish. Some specimens have been known to take dried foods, but this is the exception rather than the rule. It’s likely that young fish will be easier to wean onto these.

Behaviour and CompatibilityTop ↑

As unsuitable for the community tank, as it is for the hobbyist. It is highly predatory, extremely aggressive and territorial. It also possesses a mouth full of sharp teeth and a very powerful bite. Experiments in which juveniles have been combined with other species have usually been successful for only a few months at most, and have always ended in some degree of disaster. If it does not kill tankmates straight away, it will often disfigure them irreparably. The eyes are particularly targeted, for some reason. Even much larger fish are not safe and may have chunks of flesh removed or simply be bitten into pieces.

It is also completely intolerant of conspecifics. Keep it alone and as a single specimen. Once it reaches a foot or so in length it won’t hesitate to attack you either! Extreme caution must be exercised when feeding or performing tank maintenance. A bite from even a 2 foot specimen could easily sever a finger.

Sexual Dimorphism

Unknown.

Reproduction

Unsurprisingly, captive spawning has not occured. In nature, it migrates into flooded areas during the wet season and breeds amongst aquatic vegetation in areas that are rich in micro-organisms. During breeding, the male builds a large bubble nest, into which the eggs are deposited. These supposedly hatch in around 5 days and the adults exhibit no parental care thereafter.

NotesTop ↑

G. niloticus is the only species in its genus and is utterly unique. Unlike other knifefish it has an extended dorsal rather than anal fin giving rise to the alternative common name of upside-down knifefish. Despite this common name, it is actually more closely related to the Mormyrid group of species. It is a truly beautiful sight in motion despite its lack of bright colours, as it can move in virtually any direction with ease using its undulating dorsal fin to ‘steer’. It also produces a weak electrical discharge which is used for both electrolocation (navigation) and communication. Interestingly, if a conspecific producing electricity of a similar frequency is nearby the signals interfere with one another and the fish is capable of adjusting its frequency in order to avoid this.

Alarmingly there have been batches of 2-3″ specimens being imported with increasing regularity in recent years. In addition to the fact that it is quite delicate at this size, the species is simply not suited to the home aquarium in any respect. We can only speculate as to where the majority of these fish end up, as surely only a tiny number of aquarists are able to house one for life. If you see these for sale, and they are undoubtedly amazing looking fish, ask yourself if you have the money, facilities and knowledge to house a species that can grow to 5 1/2 feet in length and could remove your hand as an adult. If you do possess these attributes, you will find that as well as being one of the most belligerent aquarium inhabitants available, it is also one of the most intelligent. A real ‘dream’ species for the lover of tankbusting predatory fish then, but a potential nightmare for the vast majority of hobbyists. There is an albino form available occasionally which is much sought after and very expensive.