Knifefish Care Sheet

THE NAME FITS

Knifefish are some of the most interesting freshwater aquarium fish available.  Their unique “knife blade” body shape and ability to swim backwards using their undulating bottom fin make them fascinating additions to appropriate aquarium communities.  Knifefish can be placed in two main groups:  The largest group belongs to the Order Gymnotiformes and are found in Central and South America.  They include ghost knives, banded knives and glass knives.  A smaller group, in the Family Notopteridae, are native to Southeast Asia and Africa and include featherfin, African and clown knives.  Most knifefish have the ability to generate and receive electrical discharges, which they use for navigation, locating prey and communication.  Knifefish are not for beginning aquarists due to their specialized feeding requirements and, in some cases, large adult size.

NATURAL HABITAT

Knifefish occupy a variety of habitats in the wild, including lakes and large rivers.  Several species move into flooded forests during the wet season to breed.  While most species inhabit quiet water with abundant vegetation, glass knives prefer deep river channels with strong currents.  Most species are exclusively freshwater, however, a few knifefish, such as the featherfin, spend brief periods in brackish water. 

WATER REQUIREMENTS

Knifefish are scaleless, and are extremely sensitive to poor water conditions.  Water quality should be pristine, with undetectable ammonia and nitrites, and nitrates below 20 ppm.  pH should be between 7.0 and 8.0, with alkalinity between 5° and 10° (90 ppm to 180 ppm).  Temperature should be maintained between 75° and 80° F.  If the aquarium is kept in rooms below 75°, use an Aqueon aquarium heater to increase the heat.  Knife fish are also sensitive to many medications, so the use of a UV sterilizer is recommended. Maintain good filtration and change 25% of the water every week to 2 weeks using an Aqueon Aquarium Water Changer or Siphon Vacuum Gravel Cleaner.  Don’t forget to treat tap water with Aqueon Water Conditioner before refilling your aquarium!

HOUSING

Because most knifefish grow to be relatively large and live long lives, appropriate plans should be made when purchasing them.  Ghost knives, featherfin knives and African knives attain lengths of 8” to 12”, requiring an aquarium of at least 55 gallons when full grown.  Banded knives require at least 100 gallons and adult clown knives will require a 200 gallon aquarium or larger.  Aba Aba knives reach lengths of over 5 ft. in the wild and are not suitable for home aquarists.  Plenty of cover in the form of tall plants and driftwood, as well as caves and grottos should be provided to help knifefish feel safe.  Ample open areas for swimming should also be present.  Ghost knives are well suited to live planted aquariums due to their calm, peaceful nature.  When keeping large knives, use artificial plants with weighted bases to prevent them from being uprooted by their active swimming behavior. Lighting should be subdued to encourage them to come out during the day and a secure cover should be used to keep them from jumping out of the aquarium.  

BEHAVIOR/COMPATIBILITY

Most knifefish are nocturnal and tend to be shy, especially when first introduced to an aquarium.  As they settle in to their new homes, they often become more outgoing during daylight hours, especially around feeding time.  They tend to be territorial and fairly aggressive toward each other or closely related species, so they are best kept one to an aquarium with other peaceful fish that are too large to be eaten.  This is especially important with clown knives, which not only get extremely large, but are highly predatory.  Depending on the species of knifefish you keep, compatible fish include silver dollars, tinfoil barbs, angelfish, severums, festivums, larger Gouramis, and Synodontis catfish, to name a few.  Always consult an aquarium expert before buying any new fish for your aquarium.  

FEEDING

The majority of knifefish are specialized feeders, with a number of species foraging the bottom at night in search of crustaceans, worms, insects and small fish.  Clown knives, African knives and featherfin knives are active predators, and will eagerly swallow any fish they can fit in their mouth!  It’s best to try to adapt knifefish to pellet and other dry foods as soon as possible, but many will show a preference for frozen or even live foods despite the aquarist’s best efforts.  Avoid the use of feeder goldfish or livebearers as they may carry diseases and are not nutritionally suitable.  Aqueon Tropical Granules, Betta Treat, Shrimp Pellets and Cichlid Pellets are good choices for small to medium-sized knife fish, while Monster Fish Medley can be fed to larger species like clown, African and featherfin knives.  Small amounts of food can be fed after the aquarium light is turned off to accommodate their nocturnal feeding behavior.  Remove any uneaten food in the morning to avoid water quality problems.  For best results, rotate their diet daily and feed only what they can consume in 2 to 3 minutes, once or twice a day.  

BREEDING - INTERMEDIATE

Knifefish breeding by private aquarists is rare, although several species are commercially bred nowadays. 

Care Sheets