Black Ghost Knifefish – Species Profile & Facts

Disclosure: I may earn a commission when you purchase through my affiliate links. As an Amazon Associate I earn from qualifying purchases. – read more

If we’re talking about exotic fish, few species are as intriguing as the Black Ghost Knifefish. This species isn’t too popular in the aquarium trade, which is a shame, given its beauty and unique vibe, compared to other species.

The Black Ghost Knifefish is unlike any other species you may have encountered, which is why we dedicate an entire article to dissecting it. Figuratively speaking, of course.

So, let’s get into it!

What is a Black Ghost Knifefish?

The Black Ghost Knifefish is a knifefish that resides mostly in South America and ranks as a carnivorous predator.

The fish is long and rather weirdly shaped, with an aquadynamic black body and no dorsal fins. The pectoral and anal fins are merged into one veil-like fin stretching over the entire body.

The fish uses this fin to move elegantly through the water, giving it a smooth and hypnotic appearance.

The head is slightly elongated with small, black eyes that are barely visible in the dark waters that the fish will inhabit. The tail is also short and narrow, lacking any tail fin.

The fish can look quite creepy when staring at you from the dark inside of a rocky cave, which most likely contributed to its infamous reputation.

South American natives believe that the fish houses the soul of the dead, which is understandable given the fish’s ominous look.

This semi-aggressive predator will consume a variety of prey, so it makes for quite an interesting addition to your tank.

Black Ghost Knifefish Requirements

If you’re interested in acquiring your own Ghost Knifefish, know that this species requires specific living conditions to survive and thrive.

These include:

Tank Size & Setup

Given this fish’s size and activity level, you require at least 100 gallons for one specimen. The Ghost Knifefish is an active nocturnal predator that tends to cover a lot of ground in search of food.

But this is not the only reason why it requires so much space. The tank’s layout also matters a lot in this sense.

Black Ghost Knifefish come from rich and complex ecosystems with specific living conditions that you should try to replicate in the aquarium.

Some of the specifics to remember include:

  • Live plants – Vegetation is necessary not only for its beneficial effect on the environment but the sheltering capabilities as well. Live plants will allow the Black Ghost to feel safer and more comfortable in its habitat, which is always a plus.
  • Plenty of decorations – Black Ghost Knifefish are nocturnal animals that rely on their environment to keep a low profile at night. The fish needs plenty of hiding spots during the day to rest. These include caves, crevices, and any dark opening it can find around its habitat. Make sure you find safe materials to build the said caves. The Ghost Knifefish has sensitive, scaleless skin that can get easily hurt by sharp or rugged rocks.
  • Dim lights – This species consists of lurkers that like to keep to the dark. You need a low-light setup to accommodate your knifefish; otherwise, your Ghost fish will become stressed and irritated.
  • A sand substrate – Ghost Knifefish are not known as substrate diggers, but they will spend a lot of time near the tank floor. You should always go for a fine sand substrate to protect the fish against skin abrasions or scratches predisposed to infections.

Other than that, your Ghost Knifefish only requires sufficient swimming room, a good and balanced diet, and peace and quiet.

Water Requirements

Aim for environmental temperatures around 72-82 F and a pH range of 6.0-8.0. These are standard aquatic conditions for tropical fish.

The water hardness shouldn’t go over 19 dGH, and keep your knifefish in a freshwater-only setup. This species cannot tolerate any salt in its water.

Also, keep in mind that Black Ghost Knifefish are generally more sensitive to poor water conditions than your typical tropical fish. You may need to have a thorough cleaning routine in place and resort to UV lights to sterilize the environment.

UV lighting is useful against various forms of aquatic pathogens that could make your fish more prone to infections in the long run.

Feeding & Diet

Since Ghost Knifefish rank as carnivorous predators, their diet should reflect their natural preferences. Provide your fish with a balanced carnivorous diet consisting of small fish, shrimp, tubifex worms, bloodworms, insects, krill, etc.

Variation is important to prevent any nutritional deficiencies and always go for fresh food.

The Ghost Knifefish prefers live food but can consume frozen meals as well. Avoid flakes, dry food, and other types of dry options, as your knifefish will reject them.

Also, show patience. The Ghost Knifefish is quite the timid character, despite what its appearance might suggest. This may cause it to fast for several hours to a day or even more upon arrival.

To minimize the accommodation period, provide your knifefish with a variety of hiding spots, keep the lights low, and only feed it at dusk or night.

Do Black Ghost Knifefish Need a Heater?

Yes, they do. I would say that all fish need a heater, especially tropical species like the knifefish. This isn’t necessarily due to the drastic temperature requirements but more because the fish doesn’t like temperature fluctuations.

Drastic temperature shifts can cause the knifefish to become stressed or even experience temperature shock if the temperature changes are too brutal.

The heater will prevent unprogrammed temperature drops and increases, keeping the environment stable and safer.

Do Black Ghost Knifefish Need a Filter?

Yes, they absolutely do. The Black Ghost Knifefish needs a clean and stable habitat with fresh and well-oxygenated waters.

The filter is ideal in this context. Just make sure you account for the fish’s extreme body flexibility and dexterity.

It’s natural for the Ghost Knifefish to enter the filter’s tubing system or even go inside the filter casing itself (especially in canister filters.) This isn’t ideal, as you may suspect, so you need to secure the filtration system to deter the knifefish’s behavior.

In this sense, secure the filter’s intake with a piece of cloth or a sponge. Make sure you occasionally clean or replace the material because they will accumulate dirt and detritus quickly.

How Much Does Black Ghost Knifefish Cost?

Most Black Ghost Knifefish cost between $15 and $25, depending on the specimen. This is the standard price range for captive-bred knifefish because wild-caught ones are slightly more expensive.

You can get those for prices around $20-$50, but they’re quite rare in the aquarium trade. Most people sell captive-bred specimens.

This raises some natural concerns, especially due to the fish’s infamous sensitivity. Many sellers couldn’t care less for the fish’s wellbeing, so they keep them in improper environments and feed them lacking diets.

You don’t want to get a malnourished or mistreated specimen, which is why I always recommend extra caution in this case.

Make sure that the seller is trustworthy and can provide warranties regarding the fish’s health.

What is the Lifespan of Black Ghost Knifefish?

This fish can easily reach 10-15 years in captivity with good care. They can live even longer in the wild, but this varies drastically based on the environmental conditions and the presence of natural predators. The fish’s lifespan will also vary in captivity.

The most common factor influencing the fish’s lifespan is the genetic makeup. Some fish will simply live longer than others, and there’s virtually nothing you can do about that.

Other factors worth mentioning include diet, overall care, stress levels, water parameters, etc.

How Big do Black Ghost Knifefish Get?

The Black Ghost Knifefish can reach 20 inches in captivity, which explains the fish’s need for so much swimming space.

A 20-inch knifefish can become a real threat to all its tankmates, so we’ll discuss this aspect shortly.

You can boost the knifefish’s size and growth rate by providing it with a good diet, optimal living parameters, and peaceful tankmates to minimize stress. Impeccable tank hygiene is also necessary for this sense.

Are Black Ghost Knifefish Aggressive?

Yes, they are. To be honest, they rank as semi-aggressive, but you might as well skip the ‘semi’ part.

Don’t get it mistaken, this is an aggressive predator that won’t hesitate to hunt down any tankmate it sees as prey. And, for knifefish, most fish look like prey.

Fortunately, there are some compatible tankmates to consider, so let’s discuss those!

Black Ghost Knifefish Tankmates

Interestingly enough, the Ghost Knifefish is actually not that bad of a tankmate. It can cohabitate with plenty of peaceful fish species like some cichlids, discus fish, Corydoras schools, and other catfish.

You can even pair your Ghost with tetras, guppies, and rasboras, for instance, but only if the knifefish is still in its juvenile years. It will eat these species once it grows large enough.

The 2 primary things to remember here are:

  1. Sufficient space – Few things are as important for the knifefish as the available space. These are territorial animals that will set their hunting grounds carefully, so they need ample swimming space. The extra space will also create a chiller environment with fewer tensions, given that all fish have sufficient room to flee in case of problems.
  2. Plenty of hiding spots – These are necessary for both the ghost knifefish and its tankmates. Rocks, driftwood, plants, and other decorative elements are great for breaking the line of sight between fish and contribute to a more peaceful and safe setting.

When it comes to having multiple Ghost Knifefish, just forget about it. While it is possible to pair 2 Ghost Knifefish, it is unlikely you can manage it.

These fish tend to be extra aggressive towards members of their own species or even fish similar in appearance.

You can house 2 of them together, provided you increase the tank’s size dramatically, but that’s not worth the effort in my book.

That’s because things can still go south, even with the extra space available. Ghost Knifefish are likely to resort to violence as their primary means of social interaction.

The extra space will only postpone that moment, but it will come.

Are Black Ghost Knifefish Good for Beginners?

No, they’re not. These fish are pretentious and more sensitive than your typical tropical aquarium fish.

They need too much space, tank maintenance, and a personalized setup that may be difficult to implement.

I recommend skipping this one if you’re a complete novice in the aquarium trade. If you feel you can handle them, just learn as much as possible about the species beforehand.

This is the only way to know if it’s worth the effort. Fortunately, Ghost Knifefish aren’t really expensive or rare, so you won’t be penalized too harshly if you mess your first project up.

How to Tell if Black Ghost Knifefish is Male or Female?

It’s hard to sex the Black Ghost Knifefish; almost as hard as breeding them. The only noticeable, although unreliable difference between males and females lies in the position of the eyes.

Males have them located more on the top of the head, while females have them in the front.

But even this difference is rather subtle and may not always be reliable.

How do Black Ghost Knifefish Breed?

The breeding process is typical, with the male courting the female to convince her of his charms. Once the first battle is won, the female will lay the eggs, and the male will fertilize them shortly after.

This is where the adults’ role ends because the Ghost Knifefish has no parental instincts. It’s normal for knifefish to eat their own eggs and even the fry in some cases.

If you feel confident enough to attempt to breed the Ghost Knifefish, invest in a breeding tank. Although, I advise against it.

This species is notoriously difficult to breed in captivity; so difficult that there are no recorded successful attempts.

The only verified sources go back to specialized fisheries in exotic countries like Indonesia, and they even had to overcome serious milestones to succeed.


The Black Ghost Knifefish is the perfect aquatic pet for those who love mysterious and dark aquatic predators.

It’s even better that the Black Ghost Knifefish is also charming and calm for the most part. Many people have reported training the fish to eat from their hands.

Just keep in mind that the fish isn’t meant for inexperienced aquarists.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.

Related Articles

Leave a Comment

Your email address will not be published. Required fields are marked *