Black Ghost Knife Fish Care: Guide | Aquascape Addiction

Black Ghost Knife Fish Care: Guide

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The ultimate Black Ghost Knife Fish care guide that covers all you need to know including tank size, feeding, temperature, tank mates, diseases and more.

Black Ghost Knife Fish Care: Guide

One of the coolest fish to get for your aquarium by far is the Black Ghost Knife Fish. It is a big, elegant, and fairly friendly fish, one that actually likes to sit in the hands of its owner as it eats. This is a very fancy tropical fish that requires a decent amount of knowledge and skill to maintain.

Even though they require a fair amount of maintenance, people seem to love them for one reason or another. Let’s not waste any more time and talk about everything there is to know about the Black Ghost Knife Fish.

If you have a knife fish, or plan to get one, this guide will tell you everything you need to know to keep the Black Ghost Knife Fish healthy and happy.

General Information

The Black Ghost Knife Fish is also known by its scientific name, the Apteronotus albifrons. They are one of the most popular types of knife fish as they have been imported to North America and Europe for close to 100 years as pets.

They come from the tropical regions of South America, especially in places that connect to the Amazon River such as Brazil. You can easily tell the difference between the Black Ghost Knife Fish and other knife fish because it has a black and white banded area on the caudal region of its body.

The Black Ghost Knife Fish also usually tends to have a shorter snout than other types of knife fish. This is a big and very nice looking fish which most people keep because of its awesome aesthetics.

They also have a long undulating fin which they can use to move both forwards and backwards through the water. This fish likes to live in swift moving rivers with sand on the bottom and will migrate to flooded forests during breeding season.

They love to live in areas that have a lot of vegetation, rocks, and other natural hiding areas. Interestingly enough, the Black Ghost Knife Fish has horrible vision and is nocturnal too, so they don’t really use their eyes.

To get a bearing on its surroundings and to find food, the Black Ghost Knife Fish uses a special organ which creates an electrical field around it, which then helps the Black Ghost Knife Fish to position itself and to feel movement around it. It is like a low voltage navigation and prey finding system, almost like a form of radar, or even the sonar which whales use.

Black Ghost Knife Fish Tank Size

These fish as you will see later on, get pretty darn big and they need quite a bit of room. One single Black Ghost Knife Fish is going to need a tank that is a minimum of 100 gallons or 379 liters in size.

Each additional Black fish is going to require another extra 100 gallons of room.

So, keep in mind, these guys are big, they need a lot of space, and that means that they will also require a fair amount of maintenance.

They love to swim around and are fairly active, so having enough space for them is essential to their happiness and their survival.

How Big Do Black Ghost Knife Fish Get?

The Black Ghost Knife Fish is a fairly substantial fish in terms of size. On average, these fish can grow to be up to 20 inches in size, and in some cases can actually grow up to 25 inches in size.

They are fairly thick too, reaching up to 3 inches in width. As you can see, this is a pretty big fish so you will need to provide them with adequate space.

Ideal Black Ghost Knife Fish Temperature

The Black Ghost Knife Fish is not a cold water fish and is in fact more or less a tropical fish species.

This fish requires the water to be around 73.0 to 82.0 degrees Fahrenheit, or 22.8 to 27.8 degrees Celsius. In all likelihood this means that you will need to get a water heater for your Black Ghost Knife Fish.

Anything colder than that 73.0 degrees Fahrenheit will cause your fish to be too cold, sluggish, lose its appetite, and even worse.

Anything below the minimum temperature or above the maximum temperature is not good for the Black Ghost Knife Fish. So, be sure to have a water heater as well as a thermometer in order to keep a close eye on the temperature of the water.

Feeding: Black Ghost Knife Fish Diet

The Black Ghost Knife Fish is strictly a carnivore, so you will not have to worry about them eating the plants in your aquarium, but they also will not clean up any algae.

These fish like to eat lots of meat and because of its large size, it likes to eat a fair amount of food. The Black Knife Fish is a nocturnal fish, so they do only come out to eat at night time.

Also, these fish can be somewhat shy, and if it is not yet acclimatized to its new home, it may hide during night time feedings and wait until you are gone to eat.

However, once this fish gets used to its home, it should come out of hiding once it is feeding time. Some owners have even trained their fish to eat right out of their hands, which is quite impressive.

What Do Black Ghost Knife Fish Eat

In terms of what to feed your Black Ghost Knife Fish, do not give them any flake foods or pellets as they will not have the nutrition that it needs.

To be fair, some pellets are usable for this fish, but you need to pay close attention to the type of pellets.

They need to be pellets for carnivorous fish and should not contain any plant matter.

In terms of feeding, you should be giving your Black Ghost Knife Fish foods such as insect larvae, grown insects, worms, small shrimp, and other small fish.

If you notice that your Black Ghost Knife Fish is skittish, offer it several meals per day to coax them out of hiding.

You can choose to feed them once or several times per day, just make sure to not over feed them and only keep feeding them until they stop eating.

Ideal Environment

One thing that needs to be kept in mind when it comes to the Black Ghost Knife Fish is that they are scale-less fish, which means that they don’t have scales.

This leaves them without that extra layer of protection and does make them fairly susceptible to changes in water parameters and water conditions.

Filtration & Water Changes

This means that you need to be very vigilant with keeping track of water conditions or else your Black Ghost Knife Fish is not going to last very long.

They are very sensitive to waste in the water as well as things like ammonia, nitrite, and nitrate.

The takeaway here is that these fish require you to do weekly water changes where you change at least 30% of the water, or anywhere up to 50%.

This is a must in order to keep the water clean and clear. On that same note, you are going to need a really good filter for the Black Ghost Knife Fish, one that can handle more volume than is actually in the tank.

Ideally, you are going to want a powerful 3 stage filter that can clean the water of any waste and impurities. A 3 stage filter with mechanical, biological, and chemical filtration is extremely important for the Black Ghost Knife Fish.

You need to make sure to get a really good, powerful, and comprehensive filter if you hope to keep these guys alive.

UV Sterilizer

Another thing that you need is a UV filter. Black Ghost Knife Fish are sensitive to medications and algae build ups, both of which can be solved and treated with a good UV sterilizer (they us UV rays, like from the sun, in order to kill algae, bacteria, and other unwanted compounds in the water).

We mentioned medications because they are sensitive to them and don’t do well on things like antibiotics. The best way to keep your fish free of disease is to use a UV sterilizer, because you don’t want to have to give them any medications if at all possible.

The Substrate

These fish require a mix of sand and gravel in the bottom as a substrate, preferably a fine sandy gravel substrate that is not too large.

Keep in mind that the Black Ghost Knife Fish does not have scales so you can’t have anything too rough in the bottom or else the Black Ghost Knife Fish might get hurt on the substrate.

They do like to spend time on the bottom, often resting on it, so it needs to be fairly soft and not abrasive.

Surroundings – Decorations & Plants

Another thing that you will want to provide your Black Ghost Knife Fish with is a lot of plants, wood, rocks, caves, and other hiding places.

These fish are fairly shy and skittish, so they do feel the most comfortable when they have a good hiding place.

There is also the fact that they are nocturnal, so they like to hide and sleep during the day, which means having a good cave or hollow log to be inside of.

What some people do is to get some kind of clear tube as it will make the fish feel safe while also allowing you to see it. The point is that you need to provide a lot of good hiding places for your fish.

Keep in mind again that the Black Ghost Knife Fish does not have scales, so make sure to not get anything remotely sharp or else your fish may get injured.

On a side note, these fish like moderate to strong water currents, so you will want a water pump in order to provide them with that flow. They like to exercise so this is pretty important.


One thing that makes the Black Ghost Knife Fish easy to have in your home is that only need low to subdued lighting.

Since they are a nocturnal fish, they are used to being in the dark because night time is when they are active. These fish sleeps during the day so you don’t need any big or bright lights.

Some subdued lighting for the day time is perfect, or even no lighting at all when they are trying to sleep. The Black Ghost Knife Fish at most requires some low lighting during the nighttime, but not so it can see, because as we discussed before, they have poor vision and rely on other methods to find their food and recognize surroundings.

Water Parameters

One thing about the Black Ghost Knife Fish that is pretty convenient is that it somewhat versatile in terms of the water parameters which it requires.

First of all, the Black Ghost Knife Fish can handle a water pH level of anywhere between 6.0 and 8.0, which means that they can live in both slightly basic and slightly acidic water.

You are going to want to get a pH testing kit as well as water conditioners to correct the pH level if it goes below or above 6.0 and 8.0 respectively.

In terms of water hardness, the Black Ghost Knife Fish is also fairly versatile. It can handle a water hardness level of anywhere between 5 and 19 dGH.

As long as you have the appropriate testing kits, you will have no trouble keeping the Black Ghost Knife Fish alive and healthy.

One thing that needs to be stressed is that the Black Ghost Knife Fish is a fresh water fish and cannot handle any salinity, even brackish water would be too high in its salt content.

Black Ghost Knife Fish Tank Mates

While the Black Ghost Knife Fish will do fine with most other fish, you should not keep them with any fish small enough to fit in its mouth as it will most likely eat it.

If you keep them with other aggressive larger fish, make sure that there is enough room because they may get into fights. It is best to keep the Black Ghost Knife Fish with smaller fish (but not too small) and with larger fish that are very peaceful.

In terms of snails, shrimp, and other crustaceans, if they are small enough to eat, the Black Ghost Knife Fish will probably eat them.

Are Black Ghost Knife Fish Aggressive?

The Black Ghost Knife Fish is a fairly peaceful and non-aggressive fish, so you don’t have to worry too much about keeping them in a community tank.

We do need to stress that we say “fairly” peaceful, as they can get aggressive with smaller fish which they see as food, plus they can be somewhat aggressive with other grown Black Ghost Knife Fish.

When keeping Black Ghost Knife Fish in pairs or multiples, make sure that you have a tank of adequate size, as they will get aggressive with each other if they do not have enough space, because they can be a little territorial.


The Black Ghost Knife Fish is a fairly hardy and resilient fish, as it usually does not get sick, especially in a well-maintained aquarium, but that being said, they still can get sick.

This is because they do not have scales, so when there is bacteria in the water, there is a good chance that the Black Ghost Knife Fish can get sick. Always make sure to quarantine new fish before adding them in, and make sure that all plants and decorations have been properly treated before you add them into your Black Ghost Knife Fish tank.

A calm fish with a good environment, a well-balanced diet, and a Black Ghost Knife Fish that has everything it needs is not very susceptible disease.

These fish usually exhibit the early warning signs of most diseases very quickly, making them fairly easy to treat.

They also respond fairly well to medications, which makes them pretty easy to treat. This fish can get several diseases including:

  • Ick.
  • Skin flukes.
  • Parasitic infections.
  • Parasitic infestations.
  • Bacterial diseases.
  • Bacterial infections.

Other than the diseases listed here, the Black Ghost Knife Fish is not overly susceptible to life threatening conditions.

Commonly Asked Questions

Are black ghost knife fish bottom feeders?

For the most part yes, ghost knife fish do tend to be bottom feeders. They can be a bit shy and weary of more or less anything and everything, and the usually only come out at night.

They also try to stay close to substrate or foliage. Now, they are not only bottom feeders, but they are for the most part.

They may swim up in the water column a bit if there are plants to keep them covered and provide some privacy, but this is fairly rare.

Do black ghost knife fish need air pump?

Yes, black ghost knife fish do need an air pump. These fish consume a lot of oxygen from the water, and aerating and oxygenating the water for these fish is very important.

Even a small black ghost knife fish tank should have at least one air pump and one air stone, and they should be of a very high quality and able to produce large amounts of oxygen.

Without an air stone and air pump, it is likely that you will find your black ghost knife fish gasping for air at the top of the water (we have reviewed air pumps here).

How long does it take for a black ghost knife fish to grow?

In terms of size, a black ghost knife fish will grow to around 60 cm or 24 inches in length. If you take proper care of this creature, it should grow to its full size in roughly 2 years, give or take a couple months.

The better you take care of it, the faster it will grow and the larger it will get.

Do black ghost knife fish eat shrimp?

Black ghost knife fish are heavy carnivores and voracious eaters, not to mention quite aggressive too, and yes, they have quite a big appetite.

These fish will eat mostly anything that they can wrap their mouths around and sink their teeth into, and this does include many types of shrimp.

They may not try to eat very large shrimp, but other than those, everything else appears to be fair game.

Is a knife a blind fish?

No, black ghost knife shrimp are not totally blind, but they also cannot see very well. Their vision is not particularly well developed, as they usually have no real use for it in the wild.

They often dwell in caves and tight spaces during the day, and usually only come out during the night for feeding.

Therefore, because they have never had much need for good vision, it has not developed. That said, they do have great smell, hearing, and can sense vibrations in the water.

Do knife fish have teeth?

No, black ghost knife fish actually do not have any teeth.

These are toothless fish, and like other toothless fish, or even like many birds, they have large, sharp, and powerful beaks which they use to kill and crush their prey.

Will black ghost knife fish eat guppies?

Yes, chances are they will. Now, this is not a sure fire thing, as it does depend on the specific black ghost knife fish in question, but they have been known to eat smaller fish like guppies, tetras, small goldfish, and other small prey which they can easily catch and fit into their mouths.


As you can see, the Black Ghost Knife Fish does require a decent amount of maintenance. This is not a type of fish that you get if you have never had another fish before. You are going to need a lot of accessories, a big tank, and lots of food.

So, they are great fish to have, they are fairly friendly, not all that difficult to care for, and they look awesome too. As long as you follow all of the tips and guidelines listed above, you will have no trouble keeping your Black Ghost Knife Fish healthy and happy.