Panther knifefish
Rhamphichthys pantherinus
The Panther knifefish features a long, ribbon-like body with striking black and yellow coloration and distinctive elongated pelvic fins.
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About the Panther knifefish
This is a weakly-electric South American sand knifefish (family Rhamphichthyidae) with a long tubular snout. It is associated with soft-bottom habitats and is largely bottom-oriented; provide a soft sand substrate and secure cover. Note that some authorities have treated Rhamphichthys pantherinus as a synonym of Rhamphichthys marmoratus (provisionally), so older sources may use different names.
Also known as
Quick Facts
Size
55 cm SL
Temperament
Semi-aggressive
Difficulty
Expert
Min Tank Size
180 gallons
Lifespan
10-15 years
Origin
South America: Peru
Diet
Carnivore - live and frozen foods (worms, insect larvae, small crustaceans); may accept sinking meaty foods once settled
Water Parameters
22-28°C
5-7.5
1-12 dGH
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This species needs 22-28°C in a 180 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give it a long tank with a big footprint (think 6 ft/180 cm+ once it starts sizing up) and a sand bottom - gravel will trash that long snout and stress it out.
- Pack in cover: PVC tubes, driftwood tangles, and leaf litter-style clutter; they relax when they can wedge themselves into a dark tunnel and will sulk in a bare tank.
- Keep water quality high and stable. Species-specific temperature/pH targets should be set from a reliable reference; FishBase confirms this is a tropical freshwater species but does not provide aquarium pH/temperature on the captured page. Avoid large, sudden parameter swings.
- Run strong filtration but diffuse the flow - they like clean, oxygenated water, just not a powerhead blasting their face all day.
- Feed after lights out: earthworms, blackworms, chopped shrimp, and meaty frozen foods work great; new ones often ignore pellets for weeks, so do not panic, just keep it consistent.
- Tankmates need to be too big to swallow and too chill to harass: larger peaceful cichlids, big tetras, and calm catfish can work; skip fin-nippers and anything small enough to disappear overnight.
- Watch for electricity and stress weirdness: they can scrape their nose on rough decor, and sudden changes (big pH swings, dirty water) can lead to heavy breathing and refusing food fast.
- Breeding in home tanks is rare - you are more likely to see courtship in a huge, heavily planted/leaf-litter tank with seasonal cues (big cool-water changes), but do not buy one expecting babies.
Compatibility
Good Tankmates
- Big, calm cichlids like severums or a mellow acara - stuff that can hold its own but is not looking for a fight. The knifefish mostly minds its own business once it feels secure.
- Silver dollars (the regular Metynnis types) - fast, tough, and they dont try to pick at the knifes fins. They also stay in the upper levels so everybody has their own space.
- Thick-skinned catfish like hoplos or larger Synodontis - good because they are bottomish without being tiny, and they arent easily bullied when the lights go out and the knife gets bolder.
- Robust, non-nippy midwater fish that are too large to be eaten (species choices should be evaluated individually).
- Large plecos and other big suckermouths (common, sailfin, royal) - theyre armored and generally ignore the knife. Just make sure youve got enough wood and caves so nobody has to share the same hide.
Avoid
- Smaller fish like neons, rummynose, guppies, and most little rasboras - if it can fit in the knifes mouth, it will eventually be a midnight snack. People get fooled because it behaves all day, then hunts at night.
- Nippy or hyper stuff like tiger barbs, serpae tetras, some danios - they stress the knife out and go after fins. A stressed knifefish turns into a hiding machine and stops eating right.
- Other knifefish (including its own kind) in anything but a huge, heavily broken-up tank - they get territorial, especially once they settle in, and the weaker one usually gets run into the ground.
Where they come from
Panther knifefish (Rhamphichthys pantherinus) are South American river fish. Think big, warm, tannin-stained systems with lots of structure, soft bottoms, and a steady supply of worms and small prey in the dark. They are one of those fish that makes total sense once you see how they hunt at night.
Most of what you will read about 'knifefish' online is about ghost knives. Panther knives are a different vibe: more predatory, more sensitive, and less forgiving if the tank is sloppy.
Setting up their tank
If you try to keep this fish like a hardy community oddball, you will hate the experience. Give it space, calm water quality, and lots of cover, and it becomes a really cool, confident night hunter.
- Tank size: I would not bother under 125 gallons, and bigger is better if you want tankmates. They are long fish and they like room to turn without scraping.
- Footprint over height: a long 6-foot tank is way nicer than a tall one.
- Substrate: fine sand or very smooth small gravel. They cruise low and can beat up their underside on sharp stuff.
- Hides: big PVC tubes, driftwood tangles, and shaded caves. Give at least 2-3 legit hide options so it can pick a favorite.
- Lighting: dim, with floating plants or tinted water (botanicals) if you like that look.
- Flow and filtration: solid filtration, but not a washing machine. They handle current, but they relax more in moderate flow with calm zones.
Cover every gap. Knifefish can and will launch themselves at night. A tight lid and blocked cable cutouts save lives.
Water-wise, aim for warm and on the softer side. Stability matters more than chasing a specific pH number. If your tap is hard, you can still keep them, but you will have an easier time if you can dilute with RO or rainwater and keep nitrates low.
- Temperature: 77-82F (25-28C)
- pH: roughly 6.0-7.2 is a comfortable zone
- Hardness: soft to medium
- Ammonia/nitrite: always 0
- Nitrate: keep it low with water changes and not overfeeding
Set up at least one cave/tube where you can still see the fish. If every hide is a black hole, you will never know if it is eating until something goes wrong.
What to feed them
These are hunters. A lot of them arrive skinny because they were offered flakes and hoped for the best. Once they lock onto real food, they put on size fast.
- Best starters: live blackworms, chopped earthworms, live or frozen bloodworms, and frozen mysis
- Staples once settled: earthworms (my top pick), shrimp pieces, strips of fish fillet, quality carnivore pellets if you can convert them
- Occasional treats: live ghost shrimp or small feeder shrimp (not goldfish or rosy reds)
Feed after lights out or at least at dusk. Mine learned the routine and would come out when the room lights dimmed. If you have bold tankmates, use tongs or a feeding tube so the knifefish actually gets its share.
Avoid mammal meat (beef heart, etc.) and oily feeder fish. They foul the water and can cause long-term issues. Also skip sharp-shelled foods that can be gulped whole.
How they behave and who they get along with
Panther knifefish are mostly peaceful in the sense that they do not go looking for fights. The problem is their mouth and their job description. If it fits, it is food. If it looks like a rival knifefish, it may get bullied.
- Good tankmates: larger calm characins, bigger peaceful cichlids, medium-large catfish that will not harass it, large peaceful plecos
- Risky: fin-nippers (they will stress it nonstop), super aggressive cichlids, anything small enough to be eaten
- Not recommended: other knifefish unless you have a very large tank and a plan for separation
They are more confident if they have a dedicated hide and the tank is not a bright, bare glass box. Expect them to be a lot more active at night. You will see that slow, backward-and-forward hovering and sudden strikes once they settle in.
If your knifefish hides 24/7 for weeks, the tank is usually too bright, too busy, or the fish is being outcompeted for food at night. Fix the environment first, then worry about appetite.
Breeding tips
Breeding Panther knifefish in home aquariums is rare. Sexing is not straightforward, and getting a compatible pair plus the right seasonal cues is a whole project. Most hobbyists keep them as showy predators rather than breeding goals.
If you want to try anyway, the best path is starting with a group of juveniles in a very large tank, feeding heavy on worms, and mimicking seasonal changes: warmer temps, lots of clean water, and then a big series of water changes that simulate a rainy season. Plenty of cover and a soft sandy bottom help.
If you ever see courtship or spawning behavior, document it. Even basic notes on temperature, water changes, and foods can help the next person because reliable hobby info on this species is thin.
Common problems to watch for
Most issues with this fish trace back to two things: dirty water and starvation (usually because it never switched to prepared foods or got outcompeted at feeding time).
- Refusing food after purchase: very common. Start with live blackworms or chopped earthworms in the evening and keep the tank calm.
- Skin damage and infections: they can scrape themselves on rough decor or get burned by ammonia/nitrite. Smooth decor and clean water fix most of it.
- Ich and other parasites: they can show it after shipping stress. Raise temp carefully and treat with meds that are safe for scaleless fish, and watch oxygen levels.
- Jumping: almost always a lid issue or a nighttime scare (sudden light, banging, aggressive tankmate).
- Slow wasting: often internal parasites or chronic underfeeding. A deworming plan plus higher-calorie foods can turn this around if caught early.
Be careful with medications and salt. Knifefish are more sensitive than scaled fish. If you are not sure a treatment is safe for scaleless species, research first and start with the lowest effective dose.
My biggest practical advice: watch the belly line. A healthy Panther knife has some thickness behind the head and along the body. If it starts looking like a ribbon, do not wait. Fix feeding, reduce competition, and check for parasites before it gets too weak.
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