Centipede Knifefish

The beautiful Centipede Knife Fish has been available for many years, but has more recently begun to enjoy popularity!

The Centipede Knifefish Steatogenys duidae has a long slender body banded in rich browns and tans. It has begun to enjoy popularity more recently due to this common name now being used for it. Scientific names often just don’t instill the sense of excitement that a good descriptive common name can.

So what’s in a name? Well for the Centipede Knifefish, combine the bands on the body with the “feet” that show up on the anal fin, and you have a pattern that really does resemble a centipede.

The Centipede Knife Fish is a member of the Hypopomidae Family of Bluntnose Knifefish found in tropical South America. This group is also referred to as Grass Knifefish or Leaf Knifefish. These fish are distinguished by their snout, which is blunt and short rather than the tubular or elongated snout seen on many other types of knifefish. There are currently only three species described in the Steatogenys genus, with the Barred Knife FishSteatogenys elegans being another that is occasionally available to aquarists. These two fish are easily confused and many times it will be imported and sold as the Centipede.

They are fairly small fish, reaching a maximum size of only 8.25 inches (21cm). The body of the Centipede Knifefish is long and flat, though more rounded towards the head. It becomes narrow towards the back until it finally terminates in a thin point at the rear. It has no dorsal fin but does have an extremely long anal fin that moves in an undulating motion. It also has an electric organ that generates a very weak electric field around its body. The electrical charges from this organ, along with its undulating fins allow it to navigate its habitat in a forward or backward motion. It also helps it identifying food and other objects in the water.

This is one of the easiest of the knife fish to care for and because of its small size it make a great addition to most community tanks. The Centipede Knifefish is peaceful and will pretty much ignore other fish, though it may snack on small species. It does requires lots of good hiding places to feel secure. In a community tank it needs to be kept with other calm, non-aggressive fish as it is very sensitive to motion. Too much activity will discourage it from coming out to feed. It does best when kept with its own kind and that will help alleviate its shyness. But a school of 6 or more is needed to reduce aggression as these fish constantly tussle with each to establishing a pecking order.

The Centipede Knifefish is not nearly as sensitive to water condition changes as some of the Knife fish, but it still requires pristine water. Unfortunately its reserved nature means you may not see your fish except at feeding time. A good way around this problem is to use a clear acrylic or plastic tube as the hiding place. These fish have poor eyesight so they use electrical impulses as a sort of radar to get their bearings. So even though the tube is clear, their radar tells them that they are in a secure place. Once you figure out what and when these fish feed you will have yourself a long lived fun to watch fish.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

Habitat: Distribution / Background

The Centipede Knifefish Steatogenys duidae was described by La Monte in 1929. They are found in the Amazon River and many of its tributaries in South America, specifically in Venezuela and Brazil. The species is not listed on the IUCN Red List.

These fish inhabit deep pools of forest creeks and rivers where the water current is strong, and flooded forests during the wet season. They can normally be found laying in leaf filled substrates to avoid predators. They feed on small crustaceans and larvae.

• Scientific Name: Steatogenys duidae
• Social Grouping: Groups
• IUCN Red List: NE – Not Evaluated or not listed

Description

The Centipede Knifefish can reach up to 8.25 inches (21cm) and has a lifespan of 15 years. Its has a flat long body, fuller and somewhat cylindrical towards the head but terminating in a thin point at the rear. It has no dorsal fin but does have an extremely long anal fin starting near the pectoral fin area. This fin can move in an undulating forward or backward motion. It is tan to light brown with irregular ‘zig zag’ type dark bands. True to its name when you combine the bands on the body with the “feet” that show up on the anal fin, the result is a pattern that resembles a centipede.

This fish also has an electric organ which allows it to generate a very weak electric field around its body. The field helps with a variety of things such as identifying objects in the water, gives it spatial orientation, helps it to navigate, and helps it identify food. Males use an electric ‘stereotyped’ communication to court females.

• Size of fish – inches: 8.3 inches (20.96 cm)
• Lifespan: 15 years

Fish Keeping Difficulty

These fish like most of the other Knife fish are not very hard to care for once you get through the initial period of getting them use to their new surroundings. Feeding these fish is the most difficult part of caring for them. They are nocturnal and mainly stay at the bottom to feed. They retreat when the other tank mates are in a feeding frenzy and become extremely timid. So night time feedings are important and foods that will make it down to them before others take it.

• Aquarium Hardiness: Moderately Difficult
• Aquarist Experience Level: Intermediate

Foods and Feeding

The Centipede Knifefish are carnivores. In the wild they are nocturnal, when the sun sets and throughout the night they feed on small crustaceans and larvae. In the aquarium this is a species that prefers smaller fresh or frozen foods such as bloodworms or brine shrimp. They may eventually be trained to eat freeze dried foods but will most likely never eat any type of flake food. They are very sensitive to motion and too much activity in the tank from hyper or aggressive tank mates will discourage them from coming out to feed.

• Diet Type: Carnivore
• Flake Food: No
• Tablet / Pellet: Occasionally
• Live foods (fishes, shrimps, worms): Most of Diet
• Meaty Food: All of Diet
• Feeding Frequency: Daily

Aquarium Care

The Centipede Knife Fish needs clear and pristine waters. These fish are very sensitive to water changes and the water should be tested often to assure that you will have a healthy fish. Weekly water changes of 30 – 50% are suggested.

• Water Changes: Weekly – Do a 30 – 50% water change weekly.

Aquarium Setup

The Centipede Knifefish will usually spend their time at or near the bottom of the tank. A large well planted tank with hiding places among rocks and drift wood along with open sandy areas for swimming and feeding are needed. Because this is a gregarious species that does best in groups of 6 or more, a 55 gallon (208 l) tank is about as small as you would want to use. Use a high quality filter and provide a strong water current,

Rock structures and plants with long twisted roots make a great decor and offer hiding places for your knife Fish. But these fish do need a good amount of unobstructed swimming room as well. Clay flower pots make great caves for these fish so they have a safe place to take refuge. Some aquarists will use a clear tube for the fish to hide in. This makes it feel secure, but also the aquarist can see it. Soft sand is the best choice for substrate.

These are nocturnal fish and appreciate subdued lighting with floating plants to break up any light. To get the most enjoyment out of this fish add some Moonlight LED lights to make viewing this fish easier as they will hide when normal tank lights are on.

• Minimum Tank Size: 55 gal (208 L)
• Suitable for Nano Tank: No
• Substrate Type: Sand
• Lighting Needs: Low – subdued lighting
• Temperature: 74.0 to 82.0° F (23.3 to 27.8&deg C)
• Range ph: 6.0-6.5
• Hardness Range: 5 – 10 dGH
• Brackish: No
• Water Movement: Moderate – Provide a moderate to strong water current.
• Water Region: Bottom – The Centipede Knifefish will usually spend their time at or near the bottom of the tank.

Social Behaviors

This is a peaceful fish that will usually not bother other fish. They require good hiding places and will not do well with aggressive tank mates. The long, pointed tail just looks too appetizing to anything that’s the least bit aggressive. They are easily stressed by fish that get overly excited during feeding time. Fast moving fish in large schools are not recommended as they will put unneeded stress on the Centipede knife fish. Many times causing them to retreat to caves and not eat, causing them to eventually starve.

The Centipede Knifefish are gregarious fish and if kept singly they are extremely shy. Yet they are territorial if kept in inadequate numbers. As a group they will constantly squabble to establish a pecking order, but keeping 6 or more will help alleviate any single fish from being bullied.

• Venomous: No
• Temperament: Peaceful
• Compatible with:
  • Same species – conspecifics: Yes – Keep in groups of 6 or more. They are gregarious fish, but territorial if kept in inadequate numbers.
  • Peaceful fish (): Monitor – Though not aggressive, this fish will eat anything small enough to be considered a meal.
  • Semi-Aggressive (): Threat
  • Aggressive (): Threat
  • Large Semi-Aggressive (): Threat
  • Large Aggressive, Predatory (): Threat
  • Monitor – They ignore tank mates that are big enough to not be considered food.
  • Shrimps, Crabs, Snails: Threat – is aggressive – In the wild this fish hunts at night for worms, crustaceans, insects and snails.
  • Plants: Safe

Sex: Sexual differences

Sexual differences are unknown.

Breeding / Reproduction

It has not been bred in captivity.

• Ease of Breeding: Unknown

Fish Diseases

The biggest issue with the Centipede Knife fish is starvation and sickness caused by lack of nutrition. These fish are hardy and disease is not usually a problem in a well maintained aquarium. That being said there is no guarantee that you won’t have to deal with health problems or disease. They are sensitive to some fish medications such as copper and those containing formalin.

Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance. Because these fish eat live food, disease can be passed to them from their foods. Make sure to quarantine live food before feeding.

When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed. The best way to proactively prevent disease is to give your fish the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. A stressed fish is more likely to acquire disease.

As with most fish the Centipede Knifefish are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.

Availability

The Centipede Knifefish are commonly available.

References

• Animal-World References: Freshwater Fish and Plants
• Joseph S. Nelson, Fishes of the World, Wiley, 2006.
• Dr. Herbert R. Axelrod, Dr. Warren E Burgess, Dr. Cliff W. Emmens, Neal Pronek, Jerry G. Walls, Ray Hunziker,
  Dr. Axelrod’s Mini-Atlas of Aquarium Fishes, Mini- Edition, T.F.H. Publications, Inc., 1987
• Steatogenys duidae (La Monte, 1929), Fishbase.org