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Banded Knifefish
Gymnotus carapo
A massive, eel-like nocturnal predator reaching 60 cm. Strikingly decorated with yellow and black tiger stripes. Incredibly hardy (breathes air), but notoriously aggressive and entirely intolerant of any other knifefish. A true 'Monster Fish'.
Class:Actinopteri
Order:Gymnotiformes
Family:Gymnotidae
Genus:Gymnotus
Species:Gymnotus carapo
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Water Temperature
22 - 28 °C
pH Value
6 - 7.5
Water type
Freshwater
Adult size
76 cm
Minimum tank volume
>= 500 L
Minimum group
>= 1
GH
4 - 15 dGH
KH
2 - 7 dKH
TDS
80 - 295 ppm
Conductivity
125 - 461 uS/cm
Species description
Geographical Origin and Habitat: Omnipresent in the Amazon and Orinoco basin. Nocturnal predator of shady swamps, flooded forests (Igapó) and trickles saturated with decomposed vegetation. Capable of surviving in stagnant waters almost devoid of oxygen.
Taxonomy and Morphology: Banded Knifefish. Cylindrical and tapered shape similar to an eel, but compressed laterally. Totally devoid of dorsal, caudal and pelvic fins: it moves by undulating the immense anal fin forwards and backwards. Reaches 60 cm (24 inches).
Social Behavior: Ruthless, intolerant and solitary. Generates a weak continuous electric field to hunt and communicate in total darkness. If two Gymnotus are placed in the same tank, they will attack each other with inhuman ferocity until the death of the weaker.
Coloration and Sexual Dimorphism: Formidable camouflage. Chestnut or chocolate brown body crossed by narrow yellowish or beige oblique bands, which thicken towards the tail. Very small eyes. Impossible to distinguish the sexes visually.
Care, breeding and tankmates
Aquarium Setup: Tank for large predators (minimum 150 cm / 5 feet / 500 liters). STRICTLY requires large PVC pipes or hollow logs in which to hide perfectly during the day. Very low lights. Insert floating plants and ensure a very heavy lid: it is capable of smashing the glass to jump.
Diet and Feeding: Pure carnivore and ambush predator. Hunts at night swallowing whole fish. Must be fed with lights off with giant earthworms, crayfish, mussels and large insects. Rarely accepts pelleted feeds.
Water Quality: Primitive fish, capable of breathing atmospheric air if water is scarce (obligate aerial respiration). It is literally indestructible from a chemical point of view, enduring very high pollutant loads, acidic pH and temperatures from 22 to 28°C (71-82°F).
Compatibility and Cohabitation: Nocturnal fish-eater (Nightmare for tankmates). Any fish that enters its mouth will be devoured at night (including Tetras, Corydoras and young Cichlids). Cohabits only with real armored monsters (Pseudacanthicus, large Panaque, large Oscars) and never with conspecifics.
Aquarium Breeding: Very rare. The male digs a nest in the mud among the vegetation building a dome of foam and debris. The eggs are guarded and fiercely defended by the male until the yolk sac of the tiny predatory fry is reabsorbed.
Risks and Diseases: Has no scales. Does not tolerate copper-based drugs (they are lethal). The main risk is of a managerial nature: this colossus grows quickly and terrorizes or devours half of the aquarium inhabitants before the unsuspecting beginner realizes it.
Geographic Origin and Distribution
Omnipresent in the Amazon and Orinoco basin. Nocturnal predator of shady swamps, flooded forests (Igapó) and trickles saturated with decomposed vegetation. Capable of surviving in stagnant waters almost devoid of oxygen.
Origin
Amazon, Orinoco, and Guianas
Fish profile
- Temperament
- No verified data available
- Diet
- No verified data available
- Life expectancy
- No verified data available
- Adult size
- 76 cm
- Sex ratio
- No verified data available
- Feeding frequency
- No verified data available
- Bioload
- Extreme
- Flow
- No verified data available
- Jump risk
- No verified data available
- Reproduction
- No verified data available
- Compatibility & tankmates
- No verified data available
- Tank level
- No verified data available
The catalog's scalar value is 76 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 76 cm for this species, recorded as total length (TL). The taxonomic record consulted is Gymnotus carapo (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
The single-adult profile is classified as extreme bioload. The bioload-v2 rubric deterministically assigns this class from the verified maximum length of 76 cm; it is a catalog management category, not a direct measurement of waste output.
Window to the official scientific data of the species
Data synced on: 06/15/2026
Scientific Parameters & Models
- Trophic level
- 3.6 ± 0.56 se
- Resilience
- Medium (1.4 - 4.4 years)
- Generation time
- 3.6 years
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.0038, b = 2.92
VulnerabilityModerate vulnerability (37 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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