Black Ghost Knifefish: Care Guide, Behavior & FAQs

The black ghost knife fish (Apteronotus albifrons) is one of the largest and most misunderstood fish you can get in the aquarium hobby. These fish are known for their pitch-black coloration and uniquely shaped bodies that set them apart from other freshwater fish.

As a large, growing fish that requires a suitably sized aquarium with the appropriate water conditions, their care is trickier than other fish, making them ideal for fish keepers who have experience with caring for big fish.

The size and elegance of the black ghost knife fish can make a great centerpiece for large aquariums while having an interesting appearance.

Quick Facts about Black Ghost Knife Fish

Black Ghost Knife Fish Overview

There are around 150 different species of knife fish, with some species remaining unknown and yet to be discovered. Few knife fish species are being kept in captivity, and the black ghost knife fish is one of them.

These fish originate from the tropical waters of South America, where they inhabit freshwater river basins and tributaries in the Amazon Basin in Peru, along with the river basins in Paraguay and Venezuela.

These freshwater habitats consist of fast-moving rivers with a creek-like environment with a sandy substrate littered with rocks. There is a diverse amount of vegetation in their native South American habitat, which is why fish keepers are urged to replicate the black ghost knife fish’s habitat in captivity with live plants, rocks, and driftwood. Their native habitats are quite muddy from the substrate being disturbed while being dimly lit since not much sun reaches the water from the surrounding forests.

How Much Do Black Ghost Knife Fish Cost?

The price of a black ghost knife fish is influenced by the fish, size, age, and where you purchase it from. Most small black ghost knife fish cost around $20, while juvenile and adult specimens can be priced at $100.

This makes them a relatively inexpensive fish to purchase, and the low price might be the reason why these fish are often bought as an impulse buy and then rehomed because their large size and specific care needs can be overwhelming.

Typical Behavior & Temperament

The black ghost knife fish has an interesting behavior and temperament that is unlike many other freshwater fish. Black ghost knife fish are nocturnal and have very poor eyesight, especially in the daytime. This is why they spend most of their time sleeping during the day and being active at night.

This can be a downside to anyone wanting a fish that they can watch swim around during the day. Since they have poor eyesight, the black ghost knife fish relies on electrolocation to locate their food, communicate, and find their way around an aquarium.

It is produced by a cluster of cells on the fish’s tail that use electric organ discharge to emit (electrogenesis) and receive (electroreception) electric signals, which is beneficial to the black ghost knife fish which needs to find its way throughout the dark and murky rivers in South America.

Appearance & Varieties

The black ghost knife fish has an eel-like appearance with a slender body. The average black ghost knife fish reaches an adult length of 15 to 20 inches in size, which is considerably large. Interestingly, the black ghost knife fish is scaleless, and their body is instead covered in skin with a mucous coat.

Black ghost knife fish are typically found in a pitch-black or slightly grey-black coloration. In cases where the fish is a very dark black color, they will have a dark blue sheen to their bodies that reflects in the light.

These fish have long bodies with slight downward curves of their spine. The fish’s body is thickest by the head and starts to get narrower until it reaches the end of their cylindrical tails which have two white bands. The black ghost knife does not have a caudal or dorsal fin, and they instead have a long anal fin that runs from the base of their head to the first band on their tail.

 

How to Take Care of Black Ghost Knife Fish

Habitat, Tank Conditions & Setup

Tank Size

Black ghost knife fish can grow extremely large, which makes them better suited for big aquariums with a minimum size of 100 gallons. Ideally, you should keep an adult black ghost knife fish in a 150-gallon aquarium or larger, and your black ghost knife fish appreciate any extra space.

Even though they might look small when you first buy them from the fish store because they are still babies, they can grow up to 20 inches, so keeping them in small aquariums is not feasible.

Water Quality & Conditions

Like most other scaleless fish, the black ghost knife fish does not tolerate poor water conditions well. Ammonia and nitrite levels over 0 ppm (parts per million) can affect a black ghost knife fish, but they are more tolerant of higher nitrates.

This makes it important to cycle the aquarium first through the nitrogen cycle several weeks before introducing your black ghost knife fish into the aquarium. It is important to check the water parameters in the aquarium by using a liquid testing kit to give you an idea of how much ammonia, nitrite, and nitrate is in the aquarium.

Substrate

You can use a soft sandy substrate or soil-based substrate in a black ghost knife fish aquarium. This is similar to the sandy and muddy substrate that these fish experience in the wild. Avoid using sharp gravel or rocky substrates that can irritate the fish’s skin, since they do not have scales to protect them from injury.

Temperature

The black ghost knife fish is native to the warm climates in South America, so their tropical conditions should be replicated in captivity. This is fairly simple to achieve by using a heater set to a temperature between 73⁰-82⁰ Fahrenheit. You do not want this fish to get too chilled, as this can make them more susceptible to diseases such as ich.

Since the black ghost knife fish needs such a big aquarium, make sure that the heater wattage is suitable for the size of the tank, or it may work overtime to keep all parts of the aquarium warm.

Plants

Live plants are beneficial to black ghost knife fish as they offer shelter to them while helping to absorb excess waste that could contribute to poor water quality. Live plants also look good in an aquarium, and they can create a natural environment for the fish similar to the one they would experience in the wild.

Lighting

As a nocturnal fish, the black ghost knife fish does not need bright aquarium light. You also don’t need to add a light at night for the fish, and they would prefer being in darkness at night rather than having a blue or red light. Keeping low to moderately bright light on during the day is purely for visual purposes to help you see the aquarium better, and to help any live plants grow.

Filtration

A filtration system is important for the black ghost knife fish, and you will need one that offers biological, chemical, and mechanical filtration. Filters help prevent the water from becoming stagnant while containing beneficial bacteria that help to keep the water clean.

The filter should not produce a strong or noticeable current, as the black ghost knife fish will have difficulty swimming in these conditions since they live in slow-moving waters in the wild.

Are Black Ghost Knife Fish Good Tank Mates?

In comparison to other types of knife fish, the black ghost knife fish is relatively peaceful. Their peacefulness makes them good fish for large community tanks. However, they do not need to be kept with other fish, and they will do perfectly well when kept alone.

The black ghost knife fish usually keeps to themselves in a community aquarium, and they aren’t known for being much of a bully towards other fish. There is the issue of the black ghost knife fish using its size to its advantage when it comes to eating smaller fish that it can fit in its mouth, so it is important to choose larger species of fish to keep with them.

Any tank mates should be tropical fish since the black ghost knife fish needs a heater in their aquarium. It is also important for these fish to be peaceful and not bully the black ghost knife fish which can lead to unnecessary stress.

For each tank mate that you add to your black ghost knife fish aquarium, you need to increase the tank size. This means that if you want to create a community tank for a black ghost knife fish, then the tank will need to be way over 100 gallons to be suitable.

It is not a good idea to keep two or more black ghost knife fish in the same aquarium, as they are territorial and can be aggressive to each other. The tank will also need to be very large to give each fish their own space and territory which is unachievable for many fish keepers.

What to Feed Your Black Ghost Knife Fish

The black ghost knife fish is a carnivorous fish that prefers to eat live foods. This makes live foods a necessary part of the black ghost knife fish’s diet, especially when they are still growing. In the wild, they will eat smaller fish, insects, and invertebrates that they can fit into their large mouths.

The black ghost knife fish does not eat plants, and they should be fed a carnivorous diet in captivity. Live foods such as bloodworms, shrimp, feeder fish, and insect larvae can be fed to a black ghost knife fish, and you can occasionally feed a freeze-dried food. Protein is important in a black ghost knife fish diet, so it should ideally be fed every day.

A staple carnivorous pellet fish food can also be fed to this fish up to two times a day to ensure that they are receiving all the nutrients they need.

Keeping Your Black Ghost Knife Fish Healthy

You can ensure that your black ghost knife fish is kept healthy by doing regular water tests to determine how much ammonia, nitrite, and nitrate are in the water. Any fluctuations in water parameters can be detrimental to this fish, so maintaining good water quality is important through frequent water changes and a good filtration system.

Another way that you can keep these fish healthy is by ensuring that they are fed a high-quality diet consisting of live foods and commercial pelletized fish food. Temperature also plays a vital role in the health of this fish, and the aquarium should have a stable tropical temperature both day and night with minimal fluctuations.

Lastly, when it comes to medicating a black ghost knife fish, avoid using any medications that contain copper since this is harmful to scaleless fish can the black ghost knife fish.

Breeding

Breeding a black ghost knife fish in captivity is challenging and complicated. There are very few differences between the male and female black ghost knife fish, but it seems that females can emit higher electric signals than males.

To successfully breed these fish, you will need a very large breeding aquarium, and both fish will need to be at least 10 inches before they can begin to mate. The breeding pair should show little to no aggression toward each other and they will need a very large tank or breeding pond like Indonesian fish breeders use for these fish.

The breeding aquarium should be dark and replicate their natural environment while having lots of dense vegetation, rocks, and driftwood for the eggs to stay protected. Once the male and female black ghost knife fish have spawned, they should be removed from the breeding aquarium because they will eat the eggs and they fry.

Are Black Ghost Knife Fish Suitable for Your Aquarium?

If you have a large aquarium of over 100 gallons that contains live plants, a heater, a filter, and a soft sandy substrate, then a black ghost knife fish is worth looking into. It is best to have some sort of experience in keeping monster fish, as the black ghost fish can grow large and needs very good water parameters to thrive in captivity.

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Featured Image Credit: Podolnaya Elena, Shutterstock