Black Ghost Knife Fish: Care, Size, Lifespan, Tank Mates & More

The black ghost knife fish is a unique freshwater species that will add interest and intrigue to your aquarium. Learn how to look after these fish in our comprehensive care guide.

Black Ghost Knifefish – Quick Facts

In a rush? Check out the quick facts about Black Ghost Knifefish below.

Fish Info

Scientific NameApteronotus albifrons
Common Namesblack ghost knifefish
AppearanceLong thin black fish with a curved body resembling a knife. They have white bands around their tails.
DifficultyThe care of black ghost knifefish can be difficult as they are quite sensitive to diseases and chemicals in the water.
DistributionThe black ghost knifefish are found in tropical freshwater habitats in South America. They range from Venezuela to the Paraguay–Paraná River, including the Amazon Basin.
Lifespan10 to 15 years
ShoalingBlack Ghost Knifefish are not shoaling fish.
TemperamentThe black ghost knifefish is a shy and reclusive fish that is not very social and prefers its own company.
Keep in Groups of1 or a small group
Tank MatesCelestial pearl danios, neon tetras, large swordtails, mollies, rainbowfish, peaceful catfish, Discus, Oscars, Catfish, Giant Gourami, Severum, Angelfish
DietBlack Ghost Knifefish are not picky about what they eat and will generally eat anything they can, including insects, small fish, and small invertebrates.
Length10 to 20 inches
Sexual DimorphismThere is very little observable difference between males and females.
Breeding DifficultyIt is difficult to breed black ghost knife fish due to their need for large tanks and specialized water conditions.

Water/Tank Recommendations

Water TypeBlack ghost knife fish are a tropical freshwater fish.
Water Temperature23-27°C (73-80°F)
Water pHThe ideal water pH for black ghost knifefish is 6.5-7.
Water HardnessThe ideal water hardness for black ghost knifefish is 5-19 dH.
Tank sizeThe minimum tank size for a black ghost knifefish is 120 gallons, and the recommended tank size is 180 gallons.


The black ghost knifefish is a unique-looking freshwater fish that has been steadily growing in popularity over the years. With their long slender bodies and large mouths, it’s easy to see why!

These are hardy and low-maintenance fish that can thrive in certain types of habitats. As such, we think they make great options for both beginners and seasoned aquarists alike.

In this guide, you’ll learn everything there is to know about black ghost knifefish. By the time you’re done reading it, you’ll be ready to get one yourself!

About Black Ghost Knifefish

Black ghost knifefish are a large and stunningly beautiful freshwater species. Unfortunately, they are also quite challenging to care for, which makes them an uncommon fish in the aquarium community.

Black ghost knifefish have some distinct features that make them stand out from other fish. For one thing, they’re much larger! You might think that would lead to difficulties finding hiding places in your tank, but these creatures still manage thanks to their lack of bright or vibrant coloration.

This means you don’t need to worry about their size being too noticeable when compared to more colorful species with smaller bodies. The dark body of the black ghost knife is perfect for blending into shadows or staying hidden under plants, rocks, and driftwood.


The bodies of black ghost knifefish are long and thin, as is their tail. This feature helps them hide in crevices when they feel threatened or want to rest.

They have no dorsal or caudal fin, but they do have one large fin on their underside which stretches from near the head down to the caudal peduncle (where the tail begins).

Black ghost knifefish have two pectoral fins that can be used for steering while swimming through tight spaces or hiding among rocks and plants.

The ‘ghost’ part of their name comes from the South American belief that the fish can house the ghosts of humans.

Their Length

The average length of a fully grown black ghost knife fish is around 10 to 20 inches. Since they take up quite a bit of space, they need plenty of room when it comes to their habitat.

NOTE: These fish need a large tank (more on that below) and are usually unsuitable for small tanks.


The typical black ghost knifefish lifespan is around ten to fifteen years, but they can live even longer in good conditions. Fish kept in pristine environments tend to have a higher life expectancy.

When kept in substandard tanks and with poor water quality, the black ghost knifefish will have a much lower lifespan.

This is true of many other fish species.

To avoid health issues and shorten the lifespan significantly, it’s essential to provide these fish with clean water and a good habitat.

Sexual Dimorphism

It is very difficult to tell male and female black ghost knifefish apart.

These fish generate and emit an electric field thanks to their electric organ, it is thought that males produce more electricity than females, and this is one of the only known differences.


Black ghost knifefish prefer to live in quiet, blackwater habitats filled with dense vegetation. They are found throughout the Amazon basin and surrounding regions in South America.

These fish stay close to the bottom of a river or stream and may occasionally swim closer to the surface when there is more flow. However, if their water quality dips too much or if oxygen levels drop significantly, they will bury themselves in sand for protection.

Caring for Black Ghost Knifefish

A really important thing you should do for black ghost knifefish is to take good care of them. This means providing a high-quality, well-maintained habitat with top-notch water conditions.

These fish are highly sensitive to poor water quality, so your main job when owning one will be keeping the tank in tip-top shape (which we know you already want to do).

Make sure they have enough space and hiding places in their environment. You don’t want these shy fish feeling scared or stressed out!


Black ghost knife fish will eat anything small enough to go into their mouths, including insects, small fish, and small invertebrates.

You can provide dried foods or pellets as a primary diet source. These are great for structure and nutrients. However, they’re not very exciting!

Black ghost knife fish appreciate protein-rich snacks from time to time too! So feed them bloodworms, earthworms, shrimp, and other live foods when you have the chance. This food is packed with vitamins and minerals that help keep these fish healthy.

How Often & How Much to Feed Them

Black ghost knifefish are carnivores and eat live, frozen, or freeze-dried foods. Feed them several times a day to keep their growth rate steady.

These fish may not be able to swim up for food if you place them at the bottom of the tank. To ensure that they get enough nutrients, use aquarium tongs (they’re also great for getting rid of uneaten food).

Feed your black ghost knifefish three to four small meals every day during their juvenile phase and two large ones when they reach adulthood.

Possible Diseases

The black ghost knifefish is susceptible to all the common freshwater fish diseases.

The most common health issue for this species is Ich, which causes tiny white spots of skin to appear on its body. This infection is highly contagious and can quickly spread throughout your tank.

Black ghost knife fish are also prone to various parasitic infections from fluke worms.

These small worms usually attach themselves to the fish’s skin.

The good news is that all of these diseases are easily treatable with over-the-counter medications.

Tank Setup

A natural freshwater tank with a sand substrate is the best for black ghost knifefish. These fish are burrowers and spend most of their time at the bottom of the aquarium.

A sandy substrate will mimic their environment in South America, providing them with the comfort they need after being brought into captivity. Add some rocks and driftwood to offer hiding places.

Black ghost knife fish prefer dimmer lighting than many other tropical species, so keep that in mind when setting up your lights (make sure there’s still enough light to meet their needs).

Aquarium Size

The bare minimum tank size for a black ghost knifefish is 120 gallons, and the recommended tank size is 180 gallons.

If you would like to give your fish a more natural experience, then aim for 200+ gallons instead. The extra space will allow them to explore their habitat without fearing an attack from others.

NOTE: 120 gallons is the bare minimum when it comes to black ghost knifefish. So if you want them to thrive and live a long healthy life, don’t skimp on tank size!

Water Conditions

The ideal water conditions for black ghost knifefish are similar to the rest of their tropical fish relatives. They prefer warmer waters filled with plenty of plants and hiding places.

Oxygen-rich vegetation is important, as it will improve the water quality by breaking down toxins and releasing any impurities into the system. This makes life easier on your filtration system and reduces the chances of infection in your fish.

Black ghost knife fish do best in hard water without too many heavy minerals that could affect pH levels (too much iron can make them more prone to disease). It’s also important not to use copper-based filtration equipment since this species is quite sensitive to chemicals.


The pH level of the water should ideally be between 6.5 and 7, which is slightly on the basic side. Most black ghost knifefish owners prefer to keep it closer to 7 because they are less likely to experience health problems brought on by acidic waters (like ich).

It’s important that you check your tank every few days and add dechlorinators as needed in order to prevent any changes from occurring.

You should also perform water changes periodically to keep the quality high.

NOTE: Remember that pH levels can fluctuate as you add other chemicals and items into your aquarium, so it’s important to monitor these with regular checks. Curve this with water tests done by an experienced aquarist if you want to make sure that everything is on point.


The ideal water temperature for black ghost knifefish is between 23 and 27 degrees Celsius.


The recommended hardness for black ghost knifefish is between 5 and 19 dH. The ideal range is closer to the middle of this scale, somewhere around 12-15 dH.

While these aren’t hardy fish by any means, they can be a bit more sensitive than other species that prefer softer waters (like discus, for example). This makes it important to monitor your water conditions regularly, so you don’t end up causing damage or health problems.


Another important piece of equipment is a high-quality filter. Filtration systems are essential for removing waste and keeping the tank in good condition.

The black ghost knifefish has its own specific requirements for filtration as well. They need strong currents to stay healthy, so you will have to choose a filter that can meet those needs while still providing suitable conditions for other fish species.

Black ghost knifefish need powerful filters with adjustable water flow controls built into them.

Aquarium Plants

Plants are a must for black ghost knifefish. They need hiding places and natural plants can serve that purpose perfectly.

In their native habitats, there is an abundance of vegetation that provides these fish with plenty of places to hide from predators. The same goes for your tank!

Plants like Java moss or Amazon swords will do well in your aquarium (as long as they don’t get uprooted by the current). Provide some sheltering options so that the fish have different areas to roam.

Behavior and Compatibility

Black ghost knifefish are nocturnal and will spend most of the day hiding out in a quiet area. They’re shy fish that can easily become stressed if there’s too much activity or light around them, so it’s important to make sure they have enough space to feel comfortable during the day.

During the night, they become more active as they hunt through plants and sand looking for food (they love meaty snacks). This is when you might see your black ghost knifefish swimming around your tank!

These fish like to be left alone, so they are best suited in a tank with easy-going peaceful fish.

How Many to Keep Together

As mentioned earlier, these fish are not shoaling. They do well when kept in groups of one or just a few.

When you have multiple black ghost knifefish in the same tank, they will tend to keep out of each other’s way and occupy different areas of the aquarium. This should not be an issue as long as there is ample space for everyone.

If you’re concerned about aggression, it’s best to keep them with non-aggressive species. They do well with other shy fish that want their own space.


The black ghost knifefish is a shy and reclusive fish. They prefer to be alone most of the time and will only show signs of aggression when they feel like their territory is being invaded.

This species can also get frightened very easily, so it’s important for you to make sure that there aren’t any other aggressive or overly active tank mates in the same space as them. This might cause your black ghost knifefish some stress, which could lead to health problems.

Tank Mates

The size of a black ghost knifefish can be a problem if you’re pairing them up with smaller or more active tank mates.

This means that anything small and fast might not work out for you (like neon tetras). However, there are plenty of large peaceful fish that will get along fine with it!

Some good ideas include:


Breeding black ghost knifefish is not an easy process. It’s so difficult that most aquarists don’t attempt to breed these fish at all.

The breeding process involves a tank at least 200 gallons, and essentially replicating the conditions of the Amazon rainforest.

We suggest only attempting to breed black ghost knifefish if you are an experienced aquarist.

Are Black Ghost Knifefish Fish a Good Choice For Your Tank?

Black ghost knifefish are a beautiful freshwater fish that can add some unique color to your tank. With that said, there are several things you need to consider before getting one for yourself.

First and foremost is their sensitivity to water conditions (this includes pH levels). Due to the nature of their bodies, they do not tolerate even minor changes in hardness or acidity very well. This means you’ll need to be vigilant about changing the water regularly and ensuring that everything is kept at optimal levels (which isn’t so bad once you get used to it).

Another factor you should take into account is their potential size when fully grown. These fish reach quite a large size, so if you don’t have enough room in your aquarium for them, this probably isn’t the right species for you.


Black ghost knifefish are beautiful and unique-looking fish that will add a lot of character to your tank. There’s something about their slender bodies that is very cool!

Because they need such large tanks and are not shoaling fish, you can get away with keeping fewer of them than other species.

These fish require little maintenance as well. As long as you meet their water conditions, habitat requirements, and diet needs, there won’t be much additional work on your part.


Black ghost knifefish are a stunning fish to look at. However, they have some drawbacks that you should be aware of before getting one for your tank.

The biggest issue with black ghost knife fish is their sensitivity to water conditions and diseases. These fish can be very difficult to treat when they get sick and often die within days if not treated properly (which is why it’s so important that you do everything possible to prevent illness in the first place).

Black ghost knifefish also require a lot of attention when it comes to water parameters. The pH level and hardness must stay consistent, or these freshwater fish will suffer from stress-related illnesses.


Black ghost knifefish are a fantastic freshwater species that have been getting more attention in the aquarium community. We highly recommend giving them a shot if you’re looking for something different to add to your tank!

If you have any questions about black ghost knifefish or suggestions on ways we can improve this guide, let us know. We want to provide our readers with the most helpful and accurate information possible.

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