Caring For Your Black Ghost Knife Fish (Apteronotus Albifrons)

March 26, 2024

Black Ghost Knife Fish – that also go by their scientific name Apteronotus Albifrons – are tropical freshwater fish that look elegant and mesmerizing due to their unique shape and their color, so it’s no surprise if you’re thinking about getting one for your fish tank!

These fish are extremely popular with people who create tropical fish tank environments and they’ve been a common acquisition for many years now due to their unusual beauty and curious behavior.

Caring For Your Black Ghost Knife Fish (Apteronotus Albifrons)

When it comes to taking care of them, it’s definitely nowhere near as straightforward as looking after other freshwater fish, as they have certain special requirements and are slightly on the large side, meaning they need extra care! 

In this detailed guide, we’ll talk you through everything you need to know about caring for a Black Ghost Knife Fish, from its ideal tank size to its diet, so that when the time comes for you to get one, you’ll be fully informed and completely capable of looking after it!

Black Ghost Knife Fish Background

As mentioned before, the scientific name for the Black Ghost Knife Fish is Apteronotus Albifrons, and it belongs to the Apteronotidae family of Ghost Knife Fish.

It originates from habitats in South America that have tropical freshwater. These include Venezuela, the Paraná River in Paraguay and the Amazon Basin. 

South American tribes that lived in the Amazonian jungle believed that the souls of their deceased relatives lived on in Black Ghost Knife Fish, hence why the species became known as ‘Ghost Knife Fish’.

But, there are also other common names for them now, including Apteronotid eel and The Black Knife.

You can easily buy these fish online or in pet shops and they cost around $7. 


Black Ghost Knife Fish are nocturnal, so they’re awake at night but mostly take it easy during the daytime.

Therefore, they exhibit typical nocturnal behavior, where they hunt during the night using an electric field because they don’t have very good eyesight. They communicate with other fish in this way, too. 

They’re generally a species that like to keep out of the way of other fish and mind their own business, as they tend to be quite shy and unsociable. 

However, despite this, they do have an aggressive side which can sometimes be unleashed around other Black Ghost Knife Fish if they encroach on their space and territory, which can occur if the tank is too small and they’re crammed together.

This doesn’t mean you can’t keep two or three in the same tank, though – as long as you have one that’s big enough for them to each have their own space, they shouldn’t become aggressive towards one another. 


The main reason why Black Ghost Knife Fish are so popular amongst aquarists is because of their unique appearance.

As you may be able to figure out purely from their name, they’re completely black, aside from two white rings that they have on their tails, plus a single white stripe on their noses that usually tends to extend along their back. 

Their bodies themselves are long, thin and partially curved, making them look similar to a knife – again, hence their name! They don’t have a dorsal or caudal fin, only thin ridges on top of their bodies and skinny tails. 

They can reach up to 20 inches in length when they become fully grown, which is extremely impressive, and due to their thin, streamlined shape, they swim smoothly and seamlessly, which can be a beautiful sight to behold. 

Due to their unique body shapes, they heavily rely on their pectoral fins to swim around, which are of an average size and have a wide surface area to help with mobility.


As touched upon previously, Black Ghost Knife Fish are found in tropical freshwater territories. They live mainly in the well populated Amazon River, including in Venezuela, Paraguay and Peru, in its freshwater basins.

What these waters have in common is that they’re packed with vegetation and have loads of tiny places where the fish can hide from predators, as they can squeeze into small gaps very easily.

And these bodies of water are generally murky with low visibility – which is perfect for nocturnal creatures like these fish because they rely on their electric field to hunt and communicate anyway – and moderate water currents.

The water also tends to be warm, of course, and will have a pH which is fairly neutral.

Another extremely important factor of their habitat is that the soil beneath the water (the substrate) contains sand which is soft so it can’t do them any damage, as they don’t have any scales to protect their bodies.


When it comes to choosing and setting up the tank that you’ll need to keep Black Ghost Knife Fish in, you’re going to need to carefully cater it to the conditions of their natural habitat. 

Although they’re tolerant to a fair range of water conditions, due to the water in their natural habitat being quite murky, the ideal water parameters for them to comfortably live in include a water temperature of 73 to 80 degrees Fahrenheit, a pH level of 6.5 to 8, and a water hardness of 0 to 10 KH. 

Despite the fact that these parameters are quite flexible, Black Ghost Knife Fish can be very sensitive to water conditions that are of less than the highest standard, so it really is important that you don’t stray out of the recommended parameters for them, otherwise it could result in sickness. 

They’ll also need a tank setup that has a lot of hiding places, such as rocks (which have to be smooth) and plants, because of their timidness, and it’s very important you make sure they have extremely smooth and fine soil at the bottom of the tank to make sure they don’t injure their scaleless bodies. For this, you can use either a very fine gravel mix or sand. 

You should also make sure the tank has low lighting and a water current that’s moderate to strong. 

In terms of the size of the tank, you’ll need a minimum of 100 gallons, as these fish can grow to be very big.

And, if you’re looking to keep more than one Black Ghost Knife Fish, you’re going to have to add around 80 to 100 gallons onto the tank size for each fish that you want to introduce. 


Black Ghost Knife Fish

Black Ghost Knife Fish are carnivorous fish and usually, within their natural habitat in the wild, they feed on worms, small fish, insect larvae and juveniles.

Therefore, when it comes to the food you give them in their tank, the best option is to feed them fresh or frozen creatures, like bloodworms, blackworms or brine shrimps.

Or, alternatively, if you can’t get hold of these, they’ll also eat tubifex worms, prawns, crickets or krill. 

They don’t really like dry food, so avoid giving them flakes or pellets – they might get used to eating them, but it could take a while, and it’s not as satisfying for them to eat anyway.

Because this is a nocturnal species, you’ll need to work around their sleeping habits, so the best thing to do is to only feed them once a day in the evening or the night.

It’s also imperative you don’t overfeed them, as this will make them produce extra waste in their tank water, which can lead to serious diseases (more on that later!). 


Despite the fact that Black Ghost Knife Fish can get slightly aggressive when their space is intruded upon, they are still perfect to keep with other types of fish.

As long as they have enough tank space to be able to roam around freely in and lots of readily available hiding places, there shouldn’t be any fights between them and the other fish.

Ideal tankmates for them include other peaceful fish of a similar size, such as Catfish, Discus, Corydoras, Angelfish, or Cichlids that are peaceful (some types of Cichlids aren’t!).

Corydoras are particularly great tankmates for them because they help to keep the tank clean, which will also help to prevent them from getting any horrible diseases

Obviously it’s important to make sure the tankmates you decide to get for them require the same water parameters, so species such as Goldfish aren’t adequate companions as they prefer colder water conditions. 

It’s not a good idea to keep them with small fish or creatures like shrimps and snails either, because they’ll end up eating them during the night, as this is what they consider to be food for them in the wild.


It’s not a good idea to breed Black Ghost Knife Fish, as it comes with a lot of potential issues.

Barely anyone has ever managed to breed them and raise a fry successfully – only a few specialized commercial fisheries have apparently bred them in Indonesia, but they’re extremely secretive about how they went about it.

The main factors that allow them to breed are big tanks, an abundance of plants, many hiding spots and flooding and draining their tank.

Then, if they do lay eggs, they usually lay them in a sheltered spot, so you might have trouble seeing them. But, so you know what to look out for just in case you can notice them, the eggs are yellow in color, around 0.08 inches in diameter.

The eggs usually take around three days to hatch – that’s if they get to that stage, because if you don’t notice them and separate their parents from them, it’s almost certain the parents will eat them, as Black Ghost Knife Fish generally do this in the wild due to a lack of parental instincts

If you do manage to save the eggs, though, once they hatch you’ll need to feed them tiny foods, such as baby brine shrimp or flakes broken into bits. 

However, we must reiterate that, due to the lack of information anyone has regarding breeding this species of fish, it would be a very bad idea to even attempt it.


As touched upon previously, Black Ghost Knife Fish are quite vulnerable to diseases. This is particularly true when it comes to skin diseases, due to the fact that they don’t have any scales on their bodies to protect them. 

As with most other freshwater fish, the main culprit to look out for is Ich, which is a disease that will cause them to have white spots on their exposed skin.

You’re also bound to notice a change in behavior, for example they tend to make quick rubbing or scratching movements on objects or on the soil at the bottom of the tank, or they might lose their appetite.   

Black Ghost Knife Fish are also prone to infections if they cut their skin, so look out for any cut that doesn’t appear to be healing properly. 

Because of these dangers, it’s very important to take some time out in your day to inspect your fish and make sure they’re looking and acting normally. 


For Black Ghost Fish, their average lifespan is around 10 years, as long as you care for them properly and constantly watch out for disease or infection. In some scenarios, they might even reach up to 15 years old. 

This means that, if you’re willing to take good care of your Black Ghost Knife Fish, they can potentially become your companion for a very long time, and 10-15 years certainly gives you plenty of time to strike up an affectionate bond with your fish!

Final Thoughts

Black Ghost Knife Fish are an extremely beautiful species of fish, so it doesn’t come as a surprise if you’re considering getting one for your fish tank.

However, taking care of them is more of a challenge than with other freshwater fish, due to the fact they’re prone to diseases. 

But, with the help of this guide, we hope you now know exactly how to care for your Black Ghost Knife Fish if you do decide to get one!
Jose Viacrucis

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