Black Ghost Knifefish: Care Guide For Night Eaters

The Black Ghost Knifefish is an unusual creature that can make a stunning centerpiece in any tropical, freshwater display aquarium. The species has been around in the hobby for many decades and has gained a large following thanks to its elegant, unusual looks, and interesting behavior.

In this guide, we introduce you to the Black Ghost and provide you with a detailed and comprehensive guide on the species’ care.

These fish can be tricky to keep and are not, therefore, recommended for beginners.

What is a Black Ghost Knifefish?

The Black Ghost Knifefish, scientific name Apteronotus albifrons, belongs to the Apteronotidae family of Ghost Knifefish and is also commonly known as the Black Ghost.

The species originates in tropical freshwater habitats in South America, specifically from Venezuela to the Paraguay Paraná River and the Amazon Basin.

Ghost Knifefish were given their name thanks to the belief of some Amazon tribes that the souls of their dead relatives inhabit these fish. Although there’s no substantive evidence to back up that tale, it’s a great story to tell visitors who admire your fish!


The Black Ghost inhabits swift-flowing, sandy-bottomed rivers, migrating into flooded forests during the wet season. The species prefers areas that are heavily planted with plenty of hiding places.

Consequently, the fish’s natural environment is rather dark, and they have poor vision. For that reason, the Black Ghost Knifefish has evolved with the unusual ability to generate low-voltage electricity that forms a kind of built-in radar system, which helps the fish to navigate through the murky waters in which it lives. That novel ability is also used for hunting and to communicate with other Knifefish.

The Black Ghost Knifefish is nocturnal, preying on worms, crustaceans, small fish, insects, and insect larvae.


The Black Ghost grows to a substantial size, reaching up to 20 inches in length.

The fish’s body is elongated and flat, tapering to a very thin peduncle. On the underside of the fish is a long, continuous fin that’s formed by the conjoining of the anal and caudal fins. This unusual finnage undulates as the fish swims, enabling it to move backward as well as forward through the water.

The fish has a matte black body, although some specimens can have a white stripe extending from the tip of the fish’s nose, and running along its back. There is a broad white collar in front of the tail fin and a further white band just before the tip of the caudal.

There are no notable differences in appearance between the two sexes.

These fish have a long lifespan of up to 15 years and will thrive in captivity if given the correct diet and water conditions.

Potential problems

Knifefish are best kept by aquarists who have some experience in fishkeeping.

Black Ghosts are scaleless fish, and they are, therefore, more susceptible to disease. Also, the fish’s lack of scales can make them hypersensitive to many medications, especially those that contain copper. Wild-caught specimens often carry parasites that can infect other fish in your collection.

For that reason, it’s recommended that you have a UV sterilizer in your aquarium. That will aid in preventing many of the diseases to which the Black Ghost Knifefish can be vulnerable.

Note that the species is highly sensitive to changes in water conditions, so it’s vital that you maintain a stable environment in your tank at all times.

The Black Ghost is a shy fish that may not eat very well when first introduced to the aquarium, which can lead to problems such as malnutrition. As these fish are nocturnal, it can make feeding them an even greater challenge. So, when you first introduce your new Black Ghost, you may need to feed him at night while he settles into his new environment.

Alternatively, if your tank size permits, you could try fitting a moonlight mood lighting system to mimic a nighttime environment that will enable you to feed your fish at a more sociable hour.

Care and maintenance

The Black Ghost Knifefish is not suitable for a beginner, as these fish require very stable aquarium conditions, and you will need a tank of an appropriately large size if you want to keep one of these giants.

Aquarium setup

The Black Ghost Knifefish can grow to reach 20 inches in length, so you do need a very large aquarium of at least 100 gallons to accommodate one of these enigmatic creatures.

As well as tank size, like all scaleless fish, the Knifefish is extremely sensitive to any changes in water conditions. You’ll need to run a high-quality filtration system with a fairly strong flow, and you must also carry out weekly partial water changes of 30% to 50%, depending on the bioload in your aquarium. Also, carry out weekly testing of the water to make sure that ammonia and nitrate levels are not spiking.

Including a UV sterilizer in your setup will help to kill diseases that could harm your fish.

These fish spend much of their time close to the bottom of the tank. Sand and fine gravel mix works best as a substrate and replicates the fish’s natural environment most closely.

Be sure to provide plenty of thick planting around the perimeters of the tank and include some driftwood and rocks too. The fish won’t eat the plants, but they do like to hide amongst the leaves during the daytime.

These fish live in the dark, murky conditions, so they prefer subdued lighting if that works for the rest of your collection.

Water parameters

The water temperature in the tank needs to be kept stable in the range of 73.0° to 82.0° Fahrenheit.

The Black Ghost Knifefish prefers a pH range of 6.0 to 8.0 with a water hardness of 5 to 19 dGH. Note that these are freshwater fish that cannot tolerate brackish water.

This river-dwelling species enjoys a moderate to strong water flow.

Diet and nutrition

The Black Ghost Knifefish is a carnivore.

In their natural environment, the fish emerge from their hiding places to hunt once the sun has set. Throughout the night, the fish feed on insects, insect larvae, worms, snails, invertebrates, and small fish. Aquarium-kept knifefish will eat fresh and frozen meaty foods, including bloodworms, blackworms, brine shrimp, and mosquito larvae.

Generally, the Black Ghost will not eat flake food, although they will sometimes take carnivore pellets. If you want to, you can include feeder fish in the Black Ghost’s diet when he is big enough to take them.

Once they have settled into their aquarium home, Black Ghosts become more confident and may venture out to feed during the day. Although, if you have a lighting system with moonlight or subdued settings, that can encourage the fish to come out to feed at more convenient times for you.

These fascinating fish have been known to take food from their owner’s hand and will even lay in your hand to eat. It goes without saying that you must be sure to keep your hands clean and free from perfumes and soap before handling your fish.

Ideally, you should offer your fish several feeds each day.


The Black Ghost Knifefish can be aggressive toward members of its own kind and with similar-looking fish. However, these fish are peaceful to the point of being timid with other species of larger tankmates.

That said, it’s best not to mix the Black Ghost with invertebrates or very small fish, which could easily become lunch for a fully grown Knifefish. Also, you cannot safely house snails or shrimp with Apteronotus albifrons.


Although some hobbyists do claim to have successfully bred Black Ghost Knifefish in a home aquarium, there’s nothing to back that up at the time of writing.

The species is bred for the aquarium trade by large commercial operations in Indonesia, but the precise method of doing so is not known at this time. It is reported that ponds are used for breeding the fish, largely due to their mature size of up to 20 inches in length. Clearly, you would need an extremely large aquarium in which to rear these fish successfully, and that’s just not feasible for most home hobbyists.


Black Ghost Knifefish are extremely hardy and are not generally prone to diseases in a well-maintained aquarium with the correct water parameters and habitat setup.

However, these fish don’t have scales, and that can make the Knifefish susceptible to some diseases, in particular, Ich or White Spot disease.


Ich is a very common disease that can affect freshwater fish. The disease is caused by the parasite, Ichthyophthirius multifiliis, a free-swimming protozoan creature that attacks sick or weakened fish. The parasite first manifests itself as a rash of tiny white spots scattered across the fish’s body, gills, and fins. Affected fish rub and flick themselves against tank decorations, plants, and the substrate in an effort to get rid of the irritating parasites.

Luckily, Ich can be treated quite effectively by using an over-the-counter product and by raising the aquarium temperature to 82o Fahrenheit for four days. That treatment disrupts the parasite’s lifecycle, and the fish usually recover quickly.

Once Ich is active in the aquarium, there’s no point in isolating affected fish. It’s better to treat the whole tank, as more fish are likely to be infected unless the water is treated to kill the parasite. Once the outbreak is controlled, carry out a 35% water change and reduce the water temperature to its normal level.

When treating disease, never use any medication that contains copper in a tank where you have Black Ghost Knifefish.

Ghost Knifefish

Other parasites

Knifefish, especially those that are wild-caught in South America, can be prone to protozoa and worm infestations, skin flukes, and other general bacterial infections following knocks and injuries.

That’s why it’s so important to quarantine your new fish so that you can watch out for potential problems before introducing him to your tank. At that time, it can be helpful to treat the tank water with an over-the-counter antibacterial product to kill off any unseen diseases that the fish may have.

Disease prevention

Whatever you add to your setup can potentially bring disease with it. That includes decorations, plants, substrate, and other fish.

Wash everything thoroughly before introducing it to your aquarium, and place new fish in a quarantine tank for at least two weeks before adding them to your main display setup.

Stress is a major fish killer. So, be sure to provide your Black Ghost with the correct water parameters, an environment that closely replicates his wild habitat, and a correct, well-balanced diet.


The Black Ghost is readily available from good fish stores or online via specialist dealers.

Until relatively recently, all the specimens that were offered for sale were taken from their natural environment and imported, primarily from Brazil. However, thankfully, the species is now widely bred in Indonesia, so the pressure has been removed from wild populations. Note that fish of five inches or more that you see offered for sale are usually wild-caught, whereas smaller specimens are most likely captive-bred imports.

Small specimens can be bought for around $10 to $20, depending on the size of the fish and its place of origin.


In this part of our comprehensive guide to keeping this fascinating species, we answer some of the questions that are most frequently asked by those considering adding one of these enigmatic fish to their collection.

Q: Is the Black Ghost Knife fish aggressive?

A: Black Ghosts are generally peaceable fish, although they can become aggressive toward others of their species, especially if your tank size is too small. You can keep more than one Black Ghost, but you will need a very large aquarium of more than 100 gallons to do so safely.

Q: How big does a Black Ghost Knifefish get?

A: These fish grow to a size of around 20 inches long.

Q: What kind of fish can you put with a Black Ghost Knifefish?

A: Black Ghosts are generally peaceful fish that get along fine with larger species. However, do not put crabs, snails, shrimp, or very small fish with Apteronotus albifrons, as they will most likely be viewed as food and eaten.

Q: Do Black Ghost Knifefish eat other fish?

A: Yes. Small fish form part of the Knifefish’s diet in the wild. Basically, any fish that is small enough to fit into the Knifefish’s large mouth will be viewed as prey.

Final thoughts

The Black Ghost Knifefish is an enigmatic creature that forms part of tribal folklore in South America from where the creature originates. For sure, their shadowy matte black color and the single, long fin that ripples beneath their body, gives the fish an otherworldly appearance. But these are peaceful, nocturnal giants who are actually rather shy and prefer to keep themselves to themselves.

These mysterious fish make an impressive addition to a freshwater tank, but because they grow to such a large size, you will need a tank size to match if you want to keep one.


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