Care Guide for Black Ghost Knifefish – 18-Inch Electrical Oddball Fish

This care guide is often requested by people because knifefish are unusual looking curiosities. They have an undulating fin which allows them to swim forward and backward. There are many types of knifefish available, but the black ghost knife (BGK), is the most common and sought-after. This pet is much larger than the average betta fish, and requires more space. It can also live over a decade. Let’s discuss what it takes for this oddball fish to be happy and healthy long-term before you commit.

What is Black Ghost Knifefish?

Apteronotus albifrons, a South American nocturnal sea fish with weak eyesight, uses electrical signals instead to navigate its surroundings. Common name “knifefish” is derived from its lack of a caudal or dorsal fin. This gives it a knife-like appearance. The knifefish’s bottom edge is covered by an anal fin that runs along the length of the body. It ripples backwards and forth like waves, allowing it to maneuver between tight spaces in a bidirectional manner.

Black ghost knifefish are often kept in captivity and can cost anywhere from $15-20 depending on their size. Many times, juveniles are sold in crowded tanks and may get into scrapes with other fish, so make sure to get a healthy one that has both of the white spots on its tail. Given that this fish can live as long as a pet dog, consider asking the store employee to feed them first so you can confirm your new knifefish is eating well before taking it home.

Find a healthy knifefish that has a good weight, active behavior, and its entire tail.

How big can a black-ghost knife get? If they get enough food, they can grow quite large. Don’t be surprised to see your baby knifefish grow into a massive 14- to 18-inch (35 to 45 cm) fish.

How fast do black ghost knife fish grow? In our care, we have seen them shoot up to 8 inches (20 cm) in the first year, and then the growth rate slows down to about 2 inches (5 cm) a year.

Does the black ghost fish live long? We haven’t found them to be very hardy. The keys to our success include feeding them really well, making sure they don’t get picked on, and maintaining good water quality, as you would with any other fish. Although fish can normally handle one stress factor, multiple stress factors can increase the risk of health problems.

Can a ghost knife fish shock you? No, it is considered to be a weakly electric fish, in contrast to a strongly electric fish like the famous electric eel that can stun its prey. An electric organ in a knifefish creates a weak electrical field. Then it has various sensing organs that can detect any distortions to this field. This is similar to a radar. This detection system helps the knifefish to navigate its surroundings, locate prey, and communicate with potential mates or intruders.

How to Set Up an Aquarium for a Black Ghost Knife

Let’s discuss tank size. A 55-gallon aquarium might be okay for the first year, but it is too small for the long term. A 75-gallon fish aquarium is the next upgrade and may last for several more years. Ultimately, we recommend getting a 120- or 180-gallon aquarium for an adult black knife fish. They can tolerate a pH between 6.8-7.8, temperature between 75 and 28degC (24-28degC), as well as GH levels of at least 5deg (90ppm). Create a heavily decorated setup with low lighting and lots of nooks and crannies – such as clear PVC pipes, rock caves, pleco caves, large driftwood, and aquarium plants. As they grow bigger, upgrade the size of their caves and tunnels so they can feel completely safe and surrounded in their shelters.

Plecos might argue with your knife fish about the best hides. Provide more caves if necessary.

Is the black ghost knifefish aggressive? In the right conditions, they can live in a community aquarium with other similar-sized, peaceful fish. It is not a good idea for tank mates to bully or outcompete them for food. Neon tetras are a favorite food of adult knifefish, as well as any small fish, so keep any nano fish away from your tank.

What kind of fish can live with a ghost knife? Some hobbyists keep adult BGKs alongside peaceful catfish, geophagus cichlids and other friendly tank mates.

Can 2 black ghost knifefish live together? We don’t recommend it since problems tend to arise. Knifefish can be territorial and won’t share their space with other electric fish like baby whale fish, elephant nose fish and other knifefish. Obviously, anything is doable if you have a large enough aquarium, but most people tend to keep ghost knifefish in undersized tanks.

What are the Black Ghost Knife Fish’s Favorite Foods?

Thankfully, they are not too difficult to feed and eat a primarily carnivorous diet. They are a bottom dweller but will eat both floating and sinking fish food. Ours enjoy a variety of worms, bloodworms, brine shrimp, pellets that fit in their mouths, and freeze-dried foods. As mentioned before, they will predate on small fish and invertebrates once they’re old enough.

Black ghost knives can be a bit shy at first and want to spend all day in their favorite hiding spot until it’s time to eat. Many people have taught their black ghost knives to eat from their hands and the water surface using floating food.

Black ghost knives can be trained to swim up to the surface and eat from your hand.

Can black ghost knife fish eat flaked food? Flaked food is not nutritionally dense enough to sustain them long-term, particularly since they are easily outcompeted by other fish for food. To help maintain their healthy weight, we prefer pellet, freeze-dried and frozen foods.

This showpiece fish is such a fun and cool-looking species to own. The black ghost knifefish is a great pet if you’ve done your research thoroughly and are ready to buy a large tank. While we do not ship fish, check our preferred online retailers to see what they have in stock.