Are Black Ghost Knife Fish Aggressive? 

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Written By Fun Fish Tanks

I Love my Fishes 

The Black Ghost Knife Fish is astounding and is popular among aquarists. The appearance of this fish is immaculate and a second look is sure once you see it. Although it is a freshwater fish, taking care of it can become a handful. They are of high maintenance than the other freshwater fishes. 

These fish are mostly nocturnal creatures that employ electrolocation to move during the night. There are a few locations in South America where black ghost knife fish are found. These fish are abundant in the Paraná and Paraguay Rivers, two bodies of water. If you follow these bodies of water, you’ll find them in Paraguay, Argentina, Venezuela, and Brazil, among other nations. 

In this article, we will discuss whether these species of fish are aggressive or not. We will go through some other aspects of its compatibility with other species as well.

Are Black Ghost Knife Fish Aggressive? 

The Black Ghost Knifefish are aggressive species of fish. But they don’t express their aggressiveness for no reason. If Black Ghost Knifefish is kept in small areas with insufficient hiding places, they will become hostile.

If maintained alongside species of the same kind or closely related species, they can also get rather boisterous. It’s doubtful that these fish will act aggressively toward one another as long as they have adequate room to call their own. Just when two or more are confined in tight quarters, they might get rather irritable. 

Are Black Ghost Knife Fish Territorial? 

Black ghost knife fish may become aggressive if their aquarium is too small or crowded. You should maintain this species in a very large tank, at least 100 gallons in size, to keep it peaceful. If you have more than one black ghost in your aquarium, you must expand its capacity by adding an extra 80 gallons for each fish. 

What fishes can Black Ghost Knife Fish live with? 

There are several appropriate Black Ghost Knife fish tankmates to choose from. It is because this species prefers to keep to itself and does not utilize its size to intimidate others. Black Ghost Knife Fish are good for a community tank. Yes, they are aggressive but won’t become aggressive unless you don’t provide them with enough space. 

The Black Ghost Knife Fish can be kept with species such as Angelfish, Corydoras, Larger Cichlids, Catfish, Tetras, Guppies, Oscars, Silver Dollars, Rasboras, and Barbs. 

You should not keep them with aggressive temperament fishes and small-sized fishes. Keeping them with small-sized fish species can be risky as Black Ghost Knife Fish can devour them. You must also avoid Bettas as they are aggressive, and Black Ghost Knife Fish will end up killing Bettas.

Can you keep two Black Ghost Knife together? 

It is possible to keep two Black Ghost Knife fish together. Although it is not recommended to keep two of them together. As they can get aggressive towards one another. If you want to keep two Black Ghost Knife Fish together, you will have to provide them with spaces large enough for both of them to swim around and call them their territory. Also, don’t increase the number from two to avoid dire consequences. 

Also, you can reduce aggression if you purchase two Black Ghost Knife Fish together since they are juveniles.

Size and Lifespan of Black Ghost Knifefish

When fully mature, the typical black ghost knife fish may reach a length of 18 to 20 inches. It also doesn’t matter the size of the tank they are in they will attain their large size. 

In terms of lifespan, the Black Ghost Knifefish usually lives for about 10 years. Their lifespan can sometimes live for 15 years. But for Black Ghost Knife Fish to live their full lifespan, proper care must be given by the owner. Proper maintenance and care are a lot important for these fish species.

Tank Size for Black Ghost Knife Fish 

As the Black Ghost Knifefish can become quite large, so its obvious that they need a large tank. These fish require a tank that is large enough to house them. Since they can reach 20 inches in size a Black Ghost Knife Fish requires a tank size of 100 gallons. 

Care for Black Ghost Knife Fish 

Water Parameters for Black Ghost Knife Fish 

Water Parameters are crucial for Black Ghost Knife Fish. These fish species find solace in water temperatures ranging from around 73°F to 80°F. The best pH levels for them are between 6.0 to 8.0. The water hardness ranges are 5 to 19 dGH. You need to maintain these parameters at all costs. 

The Black Ghost Knife Fish are very sensitive regarding the water parameters. They don’t fancy fluctuation in water parameters. They can easily get stressed and get diseases. So you must keep the water parameters within their preference and keep it stable.

Diet and Feeding of Black Ghost Knife Fish 

The Black Ghost Knifefish is a carnivorous fish. You can feed your Black Ghost Knifefish fresh or frozen bloodworms, blackworms, and brine shrimps. Tubifex worms, krill, prawns, and crickets are more options. You may also try feeding them pellets or flakes, although this may take some time for them to become used to. 

They should be provided a small amount of food each day that they can finish in a few minutes. Because they are nocturnal, you can feed them in the evening or at night.

They may struggle to eat at first. Black Ghosts are quite bashful and will take a long time to emerge from hiding. It is essential to maintain a diverse and balanced diet to ensure that your fish get the necessary vitamins and minerals for a hefty immune system.

Tank Setup for Black Ghost Knife Fish 

First of all, a large-sized tank is a must. It is critical to utilize a soft substrate. These are bottom-feeder fish, so they’ll spend a lot of time in the bottom of your tank. The optimum substrate for Black Ghost Knife Fish is fine sand or gravel. A soft is also important as these species of fish don’t have any scales and so they have delicate skin. So with a soft substrate, they won’t be harmed. 

They also need hiding places. You must also add several hiding places in their tank. Remember to get hiding places with smooth surfaces, for if you get the ones with rough surfaces they can get harmed because of their delicate skin. You can add live plants, caves, driftwood, and many more.

Diseases you should look out for 

As you already know, the Black Ghost Knife Fish has delicate skin, so they can get diseases related to their skin. They can get easily hurt and can get scratches. A small cut can develop into an infection. So watch out for any bruises or cuts on their skin and go for treatments immediately. 

Ich, the most common disease is also something you have to look out for. You will know easily if they are affected by Ich, they will develop white spots and will go through behavioral changes.

Cost of Black Ghost Knife Fish 

You can get a Black Ghost Knife Fish for $7. 


So Black Ghost Knifefish is an aggressive fish. But they don’t bully other species of fish. They show their aggressive side if they don’t have enough space for themselves. Also, they won’t back down if they are shown aggression. They will be hostile in that case. So to avoid any unwanted situations, you must keep them in a large tank and pair them up with peaceful fishes. Also, beginners might not feel comfortable with this fish species, as they are sensitive to water parameter fluctuations and have delicate skin.

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