Black Ghost Knife Fish Care Guide: Breeding, Disease, Diet

The black ghost knife fish more than earned its name with its unique appearance. Also known by their scientific name apteronotus albifrons, the black ghost knife fish is a freshwater fish native to South America.

What’s really interesting about these black ghosts, is they are nocturnal, which suggests their name is even more fitting. Black ghostknife fish are also slightly electric, which is a natural trait that helps them locate larvae.

Table of Contents

Black Ghost Knife Fish Overview

They are usually found in sandy creeks with fast flowing waters. They are also creatures of local lore, with native South Americans believing that the deceased’s spirit will inhabit the bodies of the black ghost knifefish apteronotus albifrons, which contributes to their name as well. The appearance they possess is highly unique as well (but more on that later), and they are a wonder of nature because they can both produce and receive electric signals.

If all the right conditions are met, the black ghost knife fish apteronotus albifrons will be a unique and wonderful addition to your tank.

Information ChartBlack Ghost Knife
Care Level: Medium
Temperament: Semi-aggressive
Color: Black and some white
Lifespan: 10 to 15 years
Size: 20" long
Family Apteronotidae
Diet: Carnivorous
Minimum Tank Size: 100 gallons
Temperature: 73° F to 82° F (23° C- 28° C)
Water Conditions: pH 6 to 8 with soft to medium hardness
Tank Mate Compatibility Larger and peaceful fish

Care Level for Black Ghost Knife Fish

The ghost knife fish apteronotus albifrons is quite sensitive to changes in water parameters, which is what makes them less suitable for beginners. One of the most important factors to ensuring the health and longevity of the black ghost knife is the water conditions. They are quite shy, but since they are nocturnal, they are more active at night and this can bother some of the other fish.

They are semi-aggressive, but towards you are quite tame and can even be petted, but it is advised against since it puts them at risk for certain diseases. These fish can get quite big, so you would need a large aquarium in order to maintain just a single black ghost knifefish, and the amount of space is something not a lot of aquarists have.

Black Ghost Knife Fish Temperament and Behavior

As mentioned, they are nocturnal, so much like your cat, the ghost knife fish will be active at night and tamer during the day. In order to maneuver through the waters at night, they are naturally equipped with electrolocation and electro genesis.

Much like many nocturnal animals that are active in dark conditions, the black ghost knife species have underdeveloped sight. Relying on their electric field, they can compensate for this issue. When they are first introduced to a tank, they are quite timid and it can take them a while to rear their heads. They tend to keep to themselves as a lone fish and mostly stick close to the substrate.

Is the black ghost knife fish aggressive? They are only aggressive when it comes to other knife fish, which is why it’s recommended to keep just one or at most two black ghosts (if you have enough space). Do black ghost knife fish eat other fish? Black ghosts can possibly eat other fish if they are small enough to fit into their mouths to be considered food.

Black Ghost Knife Fish
Credits to Clinton & Charles Robertson

Are Black Ghost Knife Fish Lone Or Societal In Nature? 

The black ghost knife fish is not social. It has an aggressive nature which does not go well with fish schools. They contact other black ghost knife fish or other species, but they do not mix that frequently. They are more active during the night but prefer to hang around on their own, much like a ghost. 

They like to swim around for food, and as long as they have an expanse of freshwater around them, they are happy. Their aggression flashes through when they are confined to tanks too small for their needs. These fishes have poor eyesight, and they do not like to bump into things. The recommended number of black ghost knife fish in the tank is two. Two black ghost knife fish can live in a confined space.

Black Ghost Knife Fish Appearance

There seems to be an endless list of interesting facts about the black ghost knifefish, and we have another one to add to the list . They do not have scales or fins contrary to other fish. Almost like a flying fish or a sting ray, the black ghost knifefish has billowing sides that makes it look like it glides through water. It doesn’t have a caudal or a dorsal fin either and greatly resembles a knife.

Because it doesn’t have scales, the black ghost knifefish is extra tough to care for because they are more susceptible to changes in water parameters and common fish diseases. The source of their electric reception and emission is located on their tails. It’s difficult to sex the black ghost knifefish, but studies have shown that the females have a higher electrical frequency than the males. Further studies have been made to learn more about their development.

Black Ghost Knife Fish Size

How big does a black ghost knife fish get? When they are completely stretched out, the black ghost knifefish can reach up to 20 inches long!

Black Ghost Knife Fish Size

Natural Habitat And Origin 

Every fish has a natural habitat and origin environment. The natural habitat of the black ghost knife fish is the Amazonian forest and the Amazon River and its tributaries. The rare ecosystem of the Amazon forest makes this fish a rare, beautiful species. The fish is present in Brazil, Venezuela, Peru, Ecuador, and other countries like Paraguay. The natural habitat of these fish is small rivers and streams with warm waters and cloudy streams. Such waters help the fish activate its electro navigation system with weak electrical currents from its body. 

zzThe nocturnal predator fish species of black ghost knife fish is also present in flooded mangrove rivers in the wet season. The fish thrives in the darkest corners of the Amazonian river delta, fostering its nocturnal behavior. The origin of these fishes can be traced back to the freshwater habitats of South America. The fishes grow well in the neutral waters of the Amazon


As you can imagine, the black ghost knifefish is a solid black color with only a few white decorations. The white spots are seen on their tails and their noses.

The color and the markings of the fish body help us identify a black ghost knife fish. The fish has markings on its body instead of being solid-colored ones. The color may not be bright, but it gives an overall unique appearance to the fish. Scales do not cover the body. Instead, it has smooth skin, which gives it a striking appearance. The color of the body is matte black and has around two white spots placed in a strategic location on the body. One of the markings occurs on its tail, and the other is on its nose. Sometimes this mark extends up to its back. Sometimes, the color of the fish is in varying shades of black due to environmental influences.

Lifespan of Black Ghost Knife Fish

If water conditions are maintained to a tee, your black ghost knifefish can live in the aquarium anywhere from 10-15 years!

Feeding Black Ghost Knife Fish

The black ghost knifefish is fierce-looking species that lives on a carnivorous diet. They get a steady supply of insects, larvae, smaller fish and worms in the wild. You should try to simulate this diet as much as possible in captivity. This means you would need regular feedings with bloodworms, brine shrimp and other fresh or frozen foods.

They are not picky eaters, but it could take them a while to get accustomed to fish flakes and pellets. Even when they have become accustomed to this diet, we would still suggest balancing it with regular supplements of live and frozen food. In order to know the exact amount to feed your black ghost knifefish, observe them when feeding. They shouldn’t need more than the amount they can consume within 5 min.

Be sure to feed the black ghost knifefish at night as well, since that is when they would naturally feed. Being nocturnal, you may have to get used to caring for your black ghost knifefish differently. In the beginning when they are first brought home, it will be more difficult to gauge how much to feed them because it will take them a while to come out of hiding and graze.

However, when they finally make the attempt, give them some time and make sure you clear the leftovers from the tank as soon as possible to maintain the integrity of the water. Black ghost knifefish are quite docile when it comes to their owners, and other than being very “pettable”, some aquarists have even trained their fish to feed from their hands. It could take some time and a lot of patience, but this is another option if you experience difficulty getting them to eat.

Black ghost knife fish like to feed on high protein sources. Always try to supply protein sources like worms and insects to the species. Some of the common worms that the black ghost knife fish eats as feed are Bloodworms. They also feed on brine shrimp. Insects like crickets also become the feed of these fishes.


The black ghost knifefish is from the apteronotidae family and is a tropical freshwater fish native to South America.

Black Ghost Knife Fish Care and Tank Setup

Black Ghost Knife Fish Tank Size and Specifications

Minimum Tank Size

They can grow quite large, and the minimum tank size for a single black ghost knifefish is 100 gallons. As mentioned, they are quite friendly towards other fish in an enclosed space, unless they are other knifefish or ones that resemble them. If placed with another black ghost knife fish, make sure you have a large aquarium adding 80-100 gallons per extra fish. A small aquarium tank will only lead to an increase in its aggression levels. If you have more than one black ghost knife fish, keep them in a large tank where they have ample space to move around. A high-quality filter needs to be installed because the fish is susceptible to many diseases and needs clean water at all times.

Optimum Tank Size For Black Ghost Knife Fish

The optimum tank size for a black ghost knife fish is 100 gallons.

Filter Type 

The black ghost knife fish need good quality filters for clean water. Pre-filters and canister filters are good for black ghost knife fish aquariums. A high-quality filter maintains the nitrate and ammonia levels in the water. 


The substrate needs a good soft substrate because it is a bottom feeder. A coarse substrate will only injure the delicate fish without scales. Instead, choose fine sand or small gravel as a substrate. 

How Many Fish In 100 Gallons Tank?

One black ghost knife fish needs at least 80 to 100 gallons of the tank. You can keep more than one fish in a larger tank, but you should not go above two fish. This is because keeping more than two black ghost knife fishes in one tank will cause an overlap of their electric fields, which will confuse them and stress them out.

Black Ghost Knife Fish Tank Maintenance And Care

You need to have adequate experience to handle a black ghost fish. They are extra sensitive to their anatomy, so investing in instruments such as a water filter and UV sterilizer can make your job easier. As you can imagine, the lack of scales makes the ghost fish particularly susceptible to skin diseases such as Ich (which is very common).

Tank Conditions for Black Ghost Knife Fish

The black knife ghostfish can be found all over South America, in the warmer waters of Venezuela all the way to freshwater basins in Peru. If you take a look at the rivers and streams in these areas, you will see that they are full of plants, rocks and places for the fish to dart in and out of.

Black Ghost Knife Fish Care and Tank Setup

It’s best to keep the aquarium conditions like so with murkier waters and not a lot of sunlight. In these areas, the water flow is also apparent, but not too aggressive. Since they have a more timid nature and their natural environment is full of these places, make sure you give your black ghost knifefish plenty of places to hide.

Look into plenty of rocks and vegetation. Natural plants are best but if you decide to place artificial ones, make sure that there are no sharp edges in case they injure your black ghost knifefish. The scaleless attribute is a unique one, and requires more consideration when decorating the tank.

Water Parameters For Black Ghost Knife Fish

The black ghost knife fish lives in a varied range of water parameters, making it ideal for living in an aquarium. Although the fish can live in different water parameters, it is quite sensitive to water conditions. The water quality needs to be great and well maintained at all times.


They are more accustomed to warm waters, so the temperature for the aquarium should be at 73-82 degrees Fahrenheit (23-28 degrees Celsius).

pH levels

As for the water conditions, the pH level should be relatively neutral at 6-8 and water hardness of 5-19 dGH.

Water Hardness levels 

The hardness level of water for black ghost knife fish is 0 to 10 Kh. To maintain the health of the black ghost knife fish, you have to keep testing the water conditions and create a stable environment. The water flow should also be medium to high current to mimic the riverine habitat. Since the species is fresh water in nature, avoid keeping these fishes in brackish water.

You know they are having skin issues when they start to rub themselves on surfaces around the tank. This signifies that they are itching. Their monochrome color also makes it easy to spot skin abnormalities, so keep a close watch on them.

Luckily, most skin diseases are quite easy to treat, but make sure they are never given copper-based medicine because they cannot handle it.

Black Ghost Knife Fish Tank Landscape 

The tank landscape is very important to create a suitable environment for the black ghost knife fish. The fish is predominantly nocturnal and thrives in darkness. Ensure that you provide medium to dim lighting in the tank to mimic their natural habitat. The addition of a soft substrate like fine sand and gravel mix is right for proper tank setup. Keep a lot of hiding places for the fish to stay active.

Black Ghost Knife Fish Tank Landscape

Best Plants For Black Ghost Knife Fish Tanks 

The natural habitat of black ghost knife fish has a lot of flora and greenery. Therefore, the fish in the tank also likes plants in the setup. The tank size is large and has a lot of space to install logs and plants. These also add up as hiding places for the fishes. You can add plants like Dwarf water lettuce, Hornwort, red root floater, etc. Floating plants are great for decorating the black ghost knife fish tank. 

Worst Plants For Black Ghost Knife Fish Tanks 

The worst plants for the tank will be plants that have a brackish water habitat. Plants that do not grow as sub-water species cannot be put into the tanks. 

Decorations For Black Ghost Knife Fish Tanks

There are many decorative pieces that you can put into the tank for the playful black ghost knife fish tanks. For example, you can put a ghost tube in it. A simple plastic tube set can come across as a ghost tube. The ghost tube acts as a hiding place for the fish. This way, the fish will always be visible even when hiding. You can mimic a river bed with your decorations. However, avoid hard rocks in the tankin tank décor. 

Lighting For Black Ghost Knife Fish Tanks 

The lighting for black ghost knife fish tanks should be muted and dim to mimic their nocturnal environment. The medium and dim lighting helps these beautiful fishes thrive. 

Nitrogen Requirement For Black Ghost Knife Fish Tanks

The nitrogen requirement for black ghost knife fish tanks is very low because the fish does not have scales and is very sensitive to water nitrogen levels. You need to install a high-efficiency filter to keep nitrogen optimal in the tank.

Black Ghost Compatibility & Tank Mates

When you introduce a black ghost knife fish to the tank, you must know if it was bred in captivity or captured in the wild. This is because if it’s from the wild, you may need to isolate it for a while before introducing it to the community aquarium. After all, they can transfer foreign bacteria into the tank and perhaps soil the aquarium’s condition.

The black ghost knife fish is generally considered peaceful unless they see other similar fish or other knife fish. When thinking about introducing tank mates, try to opt for ones that are similar in size (not appearance) and temperament. Cichlids can have aggressive breeds (firemouth, green terror), but peaceful ones can make great companions.

Ideal Tank Mates For Black Ghost Knife Fish 

Catfish and tetras are good with the black ghost knife fish, but make sure the aquarium mates you add are not small enough to be mistaken for food. Another instance where they can be aggressive is if the tank is too small, so make sure you have a large tank for all the species you plan to keep. A good rule of thumb is to opt for species around 10 inches (a little less is fine) and have a good disposition. Other ideal mates for a black ghost knife fish are AngelfishesBichirDiscusOscar, Geophagus, etc. A peaceful fish that does not challenge a black ghost knife fish’s space is a good match for black beauty. You can also keep a silver dollar with a black ghost knife fish if you want to make some beautiful contrasts of color in the tank. Choose tropical fishes with the same habitat as the black ghost knife fish for a peaceful tank. Keep fishes of other species but of comparable sizes with the black ghost knife fish. 

Bad Tank Mates For Black Ghost Knife Fish

Some fishes are not at all compatible with the black ghost knife fish. The most common example of such fish is small fish. The black ghost knife fish is not a bully, but it will feed on the small fishes in the night. Only when the fish is small can juvenile fishes live with them. Once their predator side is activated, do not keep small fishes in the same tank. 

Moreover, black ghost knife fish does not become a part of a mixed aquarium. You may think that it is a riverine species used to other species, but its natural predator streak does not allow other shrimpshrimps snails to live in the same tank. The black ghost knife fish will simply eat the other species. These fishes are best for one fish-only tank. 


As another general rule of thumb, do not keep black ghost knife fish with its kind or other similar species if you do not have a large enough tank. We also suggest keeping the maximum at 2 black ghost knife fish and no more than that. If you give them enough space to swim, there will less likely be fights that break out. Larger peaceful fish are the optimal choice.

Breeding Black Ghost Knife Fish 

They are very large, making it hard to breed these fish in captivity. Your aquarium will need to be very large to house both a male and a female, and in cases where there have been successful cases of breeding, the methods have been debated. They are mainly bred in commercial facilities (a large one in Indonesia), but little information is known about the process.

A pond is the better alternative to a large aquarium and can simulate the right environment much more easily. If you decide to attempt this difficult breeding, there are some conditions you must adhere to. We would also strongly advise approaching breeding with a level of caution since there is a limited amount of information and rarely any successful cases in captivity.

You need a male and female black ghost fish, which presents the most difficulty. They need to be a bonded pair that you can attempt, but it mostly happens naturally. Then the aquarium or pond comes into question. You need it to be large enough for both, so we are looking at AT LEAST 180 gallons.

This aquarium or pond would need to be in a dimly lit area without direct exposure to sunlight. It should be near a noisy area or one with a lot of foot traffic or movement. As for what goes into the tank, you need to be prepared to populate it with plenty of vegetation and rocks, and other surfaces for them to hide. Much like some other species, these fish are prone to consuming their eggs for food after spawning.

The female won’t spawn if she is stressed or feels as if she might be in danger; this is another reason why it’s so imperative to have enough hiding places in the tank.

You need to have a secure place to place the eggs or remove them. Keeping the water temperature warmer, around 27-28 degrees Celsius, is also recommended. The parents will also need flooding and draining consistently. This aquarium change will signify the wet season in South America and hopefully trigger breeding.

Pond breeding has more of a chance of success compared to aquarium breeding. For sure, you must always keep the conditions at optimal levels as these fish are extra sensitive.

Let’s say you are successful in breeding, and then you should actively remove either the eggs or the parents (the parents being the easier choice). You should see the fry in about 3 days and start with a steady diet consisting of infusoria, then some meat-based meal such as brine shrimp, and they move on the flakes. About a month or two, you can introduce them to a more varied diet when they are old enough.

Black Ghost Knife Fish Breeding Levels 


Black Ghost Knife Fish Sexual Dimorphism 

The black ghost knife fish is difficult to distinguish based on gender. It is not easy to differentiate the male from the female based on the external marks and features. You cannot identify their genders at home. However, a way to identify is to look for their eyes. The male black ghost knife fish has eyes on the top of its head. The female black ghost knife fish has eyes on the front of its head. Even though you identify their genders, breeding a pair of black ghost knife fish is always a gamble. You have to keep the aquarium very dark for the breeding to happen successfully. This is why pond breeding is more successful than aquarium breeding. 

Black Ghost Knife Fish Tanks Common Diseases And Treatments

Black Ghost Knife Fish with a swollen belly

The black ghost knife fish is very susceptible to diseases. This is because the fish lacks scales and mottled skin for protection that other fishes have. Therefore, even the smallest of injuries can lead to bacterial infections like Ich. Ich is a common disease in other freshwater fishes. The disease manifests as white spots and patches on the fish’s body. The treatment of Ich is very easy if it is done at the right time. Removing the stress factor and improving the water quality often work better than any other treatment. Sometimes, sulfur-based liquid medications added in the tank also help improve the condition of the fish. Another way is to raise the temperature of the water slightly. Since black ghost knife fish lives in warm waters, it will provide a bit of relief to them. 

Facts About Black Ghost Knife Fish 

  • Also known as Black Knife in short 
  • Amazonian tribes believe these fishes hold the spirits of the dead 
  • They live in fresh tropical water 
  • Have smooth black matte skin without scales 
  • Need moderate care level 
  • They are not social fishes and need space
  • Live a long life of about 15 years. 

Are Black Ghost Knife Fish Right For You? 

If you are enthusiastic about keeping rare fishes, the black ghost knife fish is a great pick. However, this is not the right species if you want to keep a mixed aquarium. Choose this black beauty any day if you want a lone pair of fish for company. The fish is carnivorous, so it needs special attention. The fish also needs clean, optimal conditions in its environment for a healthy life. If you are ready to fulfill these conditions, the black ghost knife fish is good.


Is The Black Ghost Knife Fish Aggressive?

No, the black ghost knife fish is not completely aggressive. It is a natural predator, but it is only aggressive in a tank when there are other knife fishes in it. Therefore, it is advised to only keep one of these large fishes or a maximum of two in a large tank.

Is It Difficult To Keep The Black Ghost Knife Fish In A Tank?

No, as long as the tank size is large and the black ghost knife fish has enough space to itself, it is not difficult to keep the fish in the tank. Keeping a black ghost knife fish as a pet is very easy once you get used to it.

Can I Give Plant Pellets To The Black Ghost Knife Fish?

The black ghost knife fish is a carnivorous fish that feeds on small insects, larvae, and shrimp. You can give these as feed to the black ghost knife fish. You can also feed the Fish some pellets occasionally, but make sure the pellets are specifically formulated for carnivorous fishes. Plant pellets are not a good option for the Fish.

Is The Black Ghost Knife Fish A Bottom Feeder?

Yes, the Fish usually stays near to the substrate or small foliage, especially during the day. It prefers to eat near the bottom and becomes more active at night. They only come up during the day if you have enough foliage on top for shade, as the Fish is a very private animal.

In What Time Period Does A Black Ghost Knife Fish Reach Its Full Size?

The black ghost knife is a large fish that reaches its full size in a matter of nearly two years. You have to take special care of its nutritional needs during the growing period.


Due to their eye-catching and unique appearance, the black ghost knifefish is an immensely popular fish in the aquarium trade. However, their beauty isn’t without a price as it also takes extra effort to care for these fish. Their temperament is one thing that doesn’t cause any problems because they are very friendly – until they meet their kind.

Other black ghost knifefish and similar-looking species can set them off, especially if your tank isn’t large enough. Due to them being scaleless fish, you also need to be extra careful about what you place in the tank. This lack of protection is precisely what makes them extra sensitive to diseases. On the bright side, the black ghost knifefish is single-colored, making it easy to spot potential issues.

Other unique traits of this fish are their electrosensory organ and being nocturnal. They have poor vision and rely on the emission and reception of these electric signals to map out their surroundings and communicate. As an aquarist and keeper of the black ghost knife fish, you need to make sure you do all your feeding (a carnivorous diet) and other interactions at night.

They are amazing additions to your tank and are trainable fish. With enough patience and time, it’s more than possible to be able to pet these fish and have them eat out of your palm.

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