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You are here: myPetSmart.com > Pet Care Library > Articles > Knife Fish

Knife Fish


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Traits & behavior

Instead of plants, these fish eat aquatic crustaceans, worms and aquatic insect larvae.

You will find that your knifefish is most active at night.

Bottom to middle swimmers
You will see your knifefish swimming in the middle or at the bottom of your aquarium. To create a beautiful environment, be sure to add some top swimmers as well. Ask a PetSmart associate to help you choose.

Knifefish can become aggressive toward other tankmates when mature.

Young schoolers
As juveniles, these fish swim in groups of five or more of the same species. As they mature, the school tends to loosen.

Things to remember

Adding fish
Whether you're just starting your aquarium or introducing new fish into your tank, don't forget to add only 1-3 at a time.

Safety & cleanliness
Please remember that all pets may bite or scratch, and may transmit disease to humans. Keep your pet's home clean and wash your hands before and after handling your pet or cleaning his home. Infants, young children, pregnant women, people with compromised immune systems, and the infirm or elderly are at greater risk of infections and should use caution when in contact with the pet or its habitat. Consult your doctor for more information..


Staple diet
Knifefish prefer all types of live foods, including tubifex worms, earthworms, bloodworms, insects, insect larvae, small fish and brine shrimp. Feed according to the directions on the packaging. They can be trained to accept frozen and freeze-dried food.

Night feedings
Because knifefish are nocturnal, they should be fed during nighttime hours with the lights turned off. Feed as much food as they will consume within five minutes.


Signs your knifefish are healthy:

  • Eating vigorously and swimming at the middle or bottom of the aquarium
  • Clear eyes, smooth, clean skin and fins free from any lesions or inconsistent colorations
  • Calm, steady gill movements

Things to watch for:

  • Lying on bottom of aquarium
  • Poor growth or weight loss
  • Inflamed gills, skin or fins
  • Fins clamped to sides
  • Scraping body on rocks

If you notice any of the signs described above, check your aquarium water quality and consult a PetSmart Aquatics Specialist.


Knifefish need a very long or large aquarium that is 40 gallons or more.

Provide plenty of hiding places in the form of rockwork and roots or a hiding tube, as well as plants on the sides and back of the aquarium, leaving room in the center for swimming.

Fish compatibility
Knifefish can share their aquarium with other large species of fish that will not nip at their fins. Be aware that they may try to eat any fish that's small enough to fit in their mouth.

Water changes
Test water weekly to assess water quality. It is recommended that 10% of your aquarium water be changed per week. At the very least, 25% of your aquarium water should be changed per month.

Water temperature
Knifefish require a tropical community aquarium with water temperatures ranging between 75-85� F. Use an aquarium heater to maintain water temperature.

Aquarium placement
Place your aquarium in a low-traffic area, away from direct sunlight and drafts.

Aquarium stand
An aquarium stand will safely support the weight of your filled aquarium.

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