The Black Ghost Knifefish has to be one of the most unusual and eye catching freshwater fish today. As you walk into any local fish store these fish seem to stand out amongst the rest of the freshwater fish as they hover around using a wave-like motion, swimming forwards and backwards. With their unusual shape and way of moving through the water they are truly unique. Due to their unusual appearance and majestic behaviour this fish has become a very popular fish in the aquarium hobby.
The Black Ghost Knifefish originates from South America; the Amazon basin, Peru and Venezuela to Paraguay in the Parana River and belongs to the genus Apteronotus, which contains around 19 species. They are nocturnal by nature so prefer to hide out a bit during the day. They can be quite shy and will hide in one place for many hours. They have also been known to be a bit aggressive towards small fish and therefore when considering keeping this species it is important to make sure that its tank mates are big enough not to get eaten.
The Black Ghost Knifefish is laterally compressed and has an elongated body, which gives them a knife-like appearance. They are black in colour with two white rings near their tail. There is also white stripe on their head extending down a few centimetres along their dorsal. This fish has a distinct swimming pattern as it swims around by using the movement of a greatly extended anal fin. Rather than swimming sideways or curving their bodies to catch prey, they will simply backtrack on stumbling across something they desire, using their long anal fin to propel themselves backwards as quickly as they would forwards, and adjust their line of attack. These are scaleless fishes and their ventral fins are non-existent. As they are scaleless they are more susceptible to infections such as white spot. They can grow as large as 50cm!
Another thing which is amazing about these fish is that they are a weak electric fish and have the ability to electro-navigate. Within the muscles of their bodies lie dedicated electricity-producing cells known as electrocytes. The charge in the knifefish originates some way towards the tail. To optimise their range, many knifefish will swim at an angle of roughly 30° with their snouts pointed downwards. This maximises the potential pick-up of the field, although it does come with a hydrodynamic burden to the fish. As mentioned this charge is weak so don’t panic – it is not anything that will ever affect you and the charge would never be noticed.
The Black Ghost Knifefish, like all knifefish, has tiny eyes and never uses vision as a hunting sense. As predators go, their prey is generally at the smaller end of the spectrum. On a forage they’ll take any food source they can fit into the mouth, which isn’t very big. Black Ghost Knifefishes are generally carnivores and will accept any meaty, fresh food. Live food such as earthworms, bloodworms, insects, insect larvae, small fish and brine shrimp are enjoyed and can also be offered as frozen/thawed food. Don’t waste your time trying to offer them dried food as they will generally not accept it. They should be fed once or twice a day (although feeding them twice is recommended because it will get them used to coming out more)
As Black Ghost Knifefish are nocturnal and therefore shy during the day, there are a few things we can provide for them in our aquarium that will make them more visible. One trick is to subdue the lighting, using red lights where possible. This is a good idea regardless and should be done, as knifefish will not naturally inhabit any areas of intense lighting, favouring dark canopies or deep river trenches in their natural habitat. Another trick is to get some lengths of clear piping. The knifefish, with their dire vision, will be unaware that they are still visible inside the tube — despite their electric senses assuring them that they are hidden!
The Black Ghost Knifefish often prefer dense tangles of décor over large and open spaces. They soon learn their way around the aquarium and become adept at moving around at amazing speeds through the tiniest of nooks and crannies. The only decorative requirement is caves, which they will soon recognise as their safe spot.
When they are small they can be easily kept in a 90 – 110 litre aquarium, although as they grow and get larger they will require a much larger aquarium of around 250-300 litres. Make sure that you have a secure lid on the aquarium as they have been known to jump. Water should be acidic and soft, with a pH of around 6.5 and a hardness up to 15°DH. They aren’t very sensitive to water chemistry or quality and so some leeway is given here. Having said that, Black Ghost Knifefish are prone to surface parasite infections, such as white spot, when kept in poor water, so make sure your water quality is good. Temperature settings of anywhere between 23- 28°C seem agreeable for many species.
Place the bag with the fish inside it in the water for 15 minutes. After 15 minutes open the bag and let it float in the water, adding about half a cup-full of water from your aquarium into the bag every 5 minutes. After about 20-30 minutes, allow your Black Ghost Knifefish to enter into your aquarium. Make sure that you don’t put a lot of water from the bag into your aquarium while getting your Black Ghost out of the bag.
When your Black Ghost Knifefish gets big it will consume small fish readily. As juveniles, these fish swim in groups of five or more of the same species. As they mature, the school tends to loosen and can become aggressive toward other tank mates. Due to this aggression between Knifefish as they get older it is usually safest to keep solitary specimens, unless attempting to breed. Aggression tends not to be displayed towards other tank mates and they tend to be aloof with many other fish. Boisterous cichlids should be avoided, as should otherwise hostile fish that could easily damage your Knifefish.
These fish have been known to interact with their owners and accept food out of their hands. They are a truly unique and majestic fish, which do well in a large aquarium that contains other larger peaceful fish. Although they might look intimidating they are very gentle with their owners and will gently swim up to you and take a treat such as a mealworm out of your hands. They have also been known to swim through their owner’s fingers back and forth. If you have a big enough tank I would highly recommended this oddball fish as an addition to your aquarium!
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