Guide to Keeping the Black Ghost Knife Fish

You don’t always want a gleaming fish in your aquarium. Sometimes you want to explore the unique side of nature by introducing an electric fish in the form of a black ghost knifefish.

Black ghost knifefish is a laid-back species that does not draw attention. It’s nocturnal and fits an experienced keeper who can provide adequate space and quality water. It also lets you put your experience to good use while standing out from the crowds.

By now, you are probably wondering, “What exactly does it take for the black ghost knifefish to thrive in my aquarium?” Don’t worry, here is the guide on how best to keep a black ghost knifefish.

Scientific Classification

Scientific name: Apteronotus albifrons
Common names: Black Knife, Apteronotid Eel
Genus: Apteronotus
Family: Apteronotidae

Species Overview

The black ghost knifefish is a South American nocturnal fish mostly found in Argentina, Venezuela, Paraguay, and Brazil. They are more frequent in the river systems of Parana and Paraguay.

The fish derives its common name, “knifefish,” from the fact that it has no caudal or dorsal fin, giving it a blade-like appearance. It instead has an extended anal fin running at the bottom of the body with back-and-forth ripples like a wave, allowing it to move between tight spaces.

The majority of black ghost knifefish on the market are captive-bred and are priced differently depending on their size. Stay vigilant when buying the fish, as it always gets into scrapes with other fish when kept in a group. Buy a healthy one without blemishes on the skin. Also, feed it at the point of sale to ensure that it is eating well before you take it home.


In the Wild

Black ghost knifefish prefer the faster rivers and streams during the dry seasons and the flooded forests during the rainy seasons. These habitats have many obstacles, one being the lack of proper lighting. However, as a nocturnal fish, it does not have or need the best eyesight. Instead, it relies on electronic signals produced by its specialized cells to navigate the surrounding area.

It can control electronic signals’ frequency, allowing it to recognize and communicate with others.

The female knifefish produces more electronic signals to increase its chances of finding potential mates through the surrounding obstacles. The signals can also work for conflict resolution, whereby the more submissive ones release more signals to avoid attacks.

Lifespan Details

Black ghost knifefish is a slow-growing fish that hangs around for a long time. With proper care, it can survive for approximately 10 to 15 years.

The fish’s lifespan generally depends on the overall care and its genetics. Providing the fish with a conducive environment increases its chances of longer-term survival.

The Appearance of the Black Ghost Knife Fish

The black ghost knife has a unique appearance, which is one of the factors contributing to its popularity.

It has a long, thin, and slightly curved body in the shape of a knife. The vertical width tapers off gradually and then thins toward the tail. It doesn’t have a caudal or dorsal fin.

The black ghost knifefish relies on its pectoral and anal fins to generate momentum, resulting in a distinct swimming style. The wave-like effect of the tail movement gives them impressive mobility for faster movements.

The pectoral fins also play a massive role in the movements. They are large and have a large surface area for propelling. The body is flat and elongated; it can reach 20 inches when fully grown, with the anal fin running along the body to the tail.

The tail has a couple of white rings that stand out due to the overall black body of the fish. While in some species, the ridge on the back can look lighter in color, the whole body is black in most cases.

The black ghost knifefish does not have any scales, making it very sensitive to water conditions and possible infections, as scales tend to provide some protection.


Most first-time keepers will be astounded by the size of the black ghost. When it’s little, the fish looks small and innocent. Most aquarists are never adequately prepared for the larger adult size.

The fish grows slowly during the first years, generally 4 to 5 inches annually through the first five years. By adulthood, they can reach up to 20 inches. These are tall sizes that a smaller tank cannot accommodate.

While some people tend to claim that the black knife can survive in small spaces, it will eventually surpass most aquariums and end up causing aggression concerns. Avoid falling victim to the notion that the fish will grow to fit the size of the tank.

Black Ghost Knife Fish Care

The black ghost knifefish requires exceptional care due to its large size, unique body type, and sensitivity. It is a great species for aquarists with a lot of experience, but it might be hard for people who have never kept fish before.

Without the scales that would otherwise protect it from diseases and other harm, consider investing in a UV sterilizer. You also have to be careful about the medicine you use for the fish. For example, avoid copper-based medications as they are very toxic to the species.

With the high risk of diseases and infections, it’s common to see the fish itch and rub within the tank. However, this is not a call for alarm, as they can heal quickly with the proper treatment. Consider increasing water temperatures when you notice signs of infection.

Food and Diet

Black ghost knifefish are full-time carnivores. They have an electrolocation system that sends electrical signals to help locate prey. Even though the fish is a bottom dweller, it can willingly go for floating and sinking foods.

At no time are the fish going to embrace commercial food fully. You must keep many live or frozen protein foods on hand for constant feeding. Some of the best options for the fish include bloodworms, crickets, krill, tubifex worms, and brine shrimp. They prey on small fish and invertebrates once they have grown old enough.

Due to their nocturnal nature, you need to master the art of timing when feeding the fish. Don’t just throw in some food when they are sleeping. Instead, consider a once-a-day meal plan, mainly in the evening or before you head to bed.

The portions you give your fish also matter. Too much food will lead to overeating and, at times, can also mean too much water contamination. However, you also don’t want to give the fish so little food that it starves. The right portion is one they can finish within a few minutes.

The fish tends to be shy in the earlier stages and spends most of the time hiding away unless it’s time to eat. You can use floating foods to encourage them to come out of hiding. Eventually, once it gets familiar with the environment, it will come out of hiding, even if it’s not time to eat. Some people have trained the fish to eat from their hands, which is impressive.

Recommended Tank Size

Black ghost knifefish can grow very large and need a large tank. The recommended minimum tank size for one fish of this species is 100 gallons. Every additional blackfish will require an additional 100 gallons of space.

Even though some aquarists think they can get away with keeping the fish in smaller tanks, it never ends well. A smaller tank size increases their aggression and is also a health hazard. The right tank size, therefore, is the best way to ensure proper living conditions.

These fish like to swim and are active enough. A larger space allows them more freedom and, thus, more happiness, which is ideal for their survival.

Proper Water Parameters

The black ghost knifefish is one of the least problematic fish in terms of water parameters. Its natural habitat is never really clean as it scavenges around for food. This means you can get away with flexible water parameter ranges.

Still, for an optimum environment, the water temperatures should be 73°F to 80°F. pH levels of 6.5 to 8 and water hardness of 0 to 10 KH.

Even though the fish can survive in a wide range of water conditions, you still need to pay attention to the quality of the water. Regular exposure to infected water increases their chances of getting infections and diseases. Also, keep the water conditions stable to avoid making the fish adjust every other time.

Observe the water’s temperature for the fish’s comfort. Extremely cold water will cause the fish to be too cold, lose its appetite, be sluggish, and have other issues. At the same time, overheated water hinders its movement.

Consider buying a solid water test kit to ensure the proper quality of the water. A quality test kit should give you accurate water level and quality readings to help you make informed decisions.

What Do They Need in Their Tank?


The Black Ghost Knifefish is a bottom fish that needs a lot going on in its environment. Provide it with plants, caves, rocks, and woods to give them a hiding place. The fish is shy and skittish and does well with hiding.

Being nocturnal, the other additions on the water provide the perfect cover when sleeping during the day. You can also opt to include a clear tube, which will make them feel safe while allowing you to also view them.

Fill the tank’s bottom with a mixture of gravel and sand. The lack of scales on the body means the fish cannot withstand anything too rough. A relatively soft sandy substrate provides the perfect place for the fish to stay as it spends a lot of time on the bottom.

This fish prefers moderate to strong water currents and also likes to exercise. You will need a water pump to help you provide a consistent supply of these conditions.

The water tank does not need so much lighting. The fish is more active at night and used to the darkness; thus, you don’t need any bright or big lights. Consider subdued lighting during the day or none as the fish sleeps. Even at night, there’s not so much need for lights. With poor vision, the fish has no use for brightness.

Another thing to include in the Black Ghost Knifefish water tank is a UV sterilizer. Considering it is sensitive to medication and algae buildup, you must always keep the water clean. A good UV sterilizer uses UV rays to kill bacteria, algae, and other unwanted compounds in the water. Removing unwanted compounds reduces the risk of infections that need medication.

Common Potential Health Problems

Black ghost fish are at a high risk of skin diseases and infections. Without scales for protection, scratches on the skin allow easy passage of bacteria and other impurities into the body.

Since they are nocturnal, they mostly only stay active at night when the lighting is not so bright; hence, you can easily miss crucial signs of infections. Therefore, you must be extra vigilant to identify signs of scrapes or wounds. On the body, white ich spots can be seen against the black skin.

Monitor scratches and cuts on the fish to ensure they are healing properly. If there’s no progress, it’s time to look for treatment options.

When infected, the black ghost fish exhibits behavioral changes. Watch out for when it starts itching and rubbing itself against everything in its surroundings.

Stress drawn from fluctuating water conditions, noise, lighting, and diet shifts is another primary health concern for the fish. Constant changes make the fish uncomfortable and increase the risk of illness and death.

The black ghost is not the best at responding to medication. You need to protect them by keeping a clean and stable environment.

Behavior and Temperament

The black ghost knifefish is an incredible species that prefers to keep to itself. With natural habitats full of obstacles, the fish prefer spaces with hiding places where they can swim in and out. In most cases, they prefer their own space without distractions.

It can become aggressive, especially with other black ghost knife fish. To avoid a power struggle, keep only a few of them together. The space available is also a factor in being aggressive. Every one of them always wants a space to call their own. As a result, whenever you add another knifefish to the tank, you should also add a larger space for exploration.

Tank Mates and Compatibility

Black ghost knifefish are predators. They eat the majority of the small fish in the area because they consider them food. So when putting the fish with others in the community, consider one of comparable size.

Even though the black ghost fish uses electrical signals to locate prey, it can’t use the same for defense. For its safety, ensure the other species you introduce in the tank are of peaceful temperament.

Best Tank Mates

As long as you can meet the water requirements, you can pair these species with different fish options like: Rope fish, Severum, Geophagus, Bichir, Angelfish, Discus, Electric blue acara, and Corydoras.

While some aquarists have managed to keep their black ghost knifefish with other species like neon tetras and celestial pearl Danios, this is only possible when the knifefish is still young. Otherwise, it will become their predator once it comes of age. The black ghost knifefish also find it hard to stay in a mixed aquarium; they will eat components like snails and shrimp. You will end up with only fish in the community in no time.

Best Ghost Knife Fish Breeding

The information about the breeding of the black ghost knifefish remains elusive. Despite the fact that there are numerous theories, none has guaranteed results. Only some fisheries in Indonesia have mastered the breeding technique; however, they are not letting any information out.

With the uncertain processes, you should keep off trying to breed the species. This is the best option, given the struggles with managing them.

There is little physical difference between the male and female black ghost knifefish. At the same time, you won’t be able to detect the electric frequencies the species discharges. This is the first challenge in personal breeding attempts.

We will update you on the best breeding practices as more information becomes available. However, the best option is to avoid trying the process in your home aquarium.

Final Thoughts

Black ghost knifefish is an interesting species that works best when looking to bring some fun to your aquarium. The fish has grown in popularity recently, and you won’t find it hard to get them in stores or online at relatively low prices.

Take note of the size of the ghost fish you are buying. Consider the juvenile ones that will grow within your set environment. Anything over 5 inches is most likely from the wild. The ones from the wild tend to have worms, flukes, Protozoa, and other bacterial infections. This is risky for the ghost knifefish and other species already in the aquarium.

While the smaller black ghosts tend to be more expensive, they are the safer option for the community. Being captive-bred means you don’t have to put them in quarantine. You also don’t have to worry about the risk of pathogens and other issues.

Even though it is not dazzling in color, keeping the black ghost knifefish gives you the bragging rights of having an electric fish. It’s the best species for you if you can provide the needed space and water quality.