Home / Fishes / Knifefish and electric eels / Banded knifefish
No federal permit to keepBanded knifefish
Gymnotus carapo
Fishes › Knifefish and electric eels (Gymnotiformes) › Gymnotidae (Electric eels and knifefish)
The banded knifefish (Gymnotus carapo) is a species of gymnotiform knifefish native to a wide range of freshwater habitats in South America.
Care at a glance
Species-specific aquarium care
- Tank: At least 150 in long and 60 in front to back for one adult (adults commonly reach about 29.9 in / 76 cm).
- Water: Freshwater.
- Temperature: 72–82°F (range recorded for this species).
- pH: 6–7.5.
- Hardness: 0–15 dGH.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Diet: FishBase classes it as a carnivore.
Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.
Care guide
Species care notes
- Tank: a base of at least 71 × 24 in (roughly 171 US gallons); space needed is rated “very large tank”.
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 72–82 °F, pH 6–7.5, 2–15 dGH.
- Behaviour: temperament predatory.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Decor isn't critical, although it does appreciate plenty of cover.”
- Diet: “Feed live and frozen foods such as bloodworm, prawns, earthworms, tubifex etc.”
- Tankmates: “Small fish will be eaten, but it can be combined with other similarly-sized species in a big enough tank.”
- Breeding: “It's not been bred in captivity, but some aspects of its breeding behaviour are known.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
South American knifefish
Applies to most species in this group. Habitat: Murky tropical rivers. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- Large, dim tanks with tubes or caves; electric eels need specialist setups and are dangerous.
Diet
- Live and frozen meaty foods.
Health watch
- Black ghost knifefish are shy and sensitive to water quality.
Understanding the animal
About this animal
About this animal
It is the most widespread species of Gymnotus, but it has frequently been confused with several relatives, including some found outside its range like the Central America G. maculosus. The English name "banded knifefish" is sometimes used for the entire genus Gymnotus instead of only the species G. carapo.
Quoted from the Wikipedia article “Banded knifefish” (CC BY-SA 4.0) 174
In the wild
In the wild
From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.1
| Where it lives | Lives in freshwater, in rivers and streams. Uses both the bottom and open water. |
| Water it lives in | Freshwater, 72–82 °F (22–28 °C), pH 6–7.5, hardness 15 dH. |
| Climate | Subtropical climate. |
| Behavior to plan for | Breeding: nesters. |
What this means for care
- Keep water within its wild range, 72–82 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 89°F (up to 92°F in the hottest sampled areas) |
| Cool-season lows | about 59°F (down to 49°F in the coldest sampled areas) |
| Average temperature | 67–80°F across sampled records |
| Relative humidity | 74–82% on average (driest month about 72%) |
| Rainfall | about 1614 mm a year |
Measured at 883 wild occurrence records sampled against WorldClim 2.1 climate data (1970–2000 averages). Air conditions in the range are ecological context, not enclosure settings: microhabitats such as burrows, leaf litter or basking rocks can be cooler, warmer or more humid.
From the sources
From the sources
Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.
| Overview | The banded knifefish (Gymnotus carapo) is a species of gymnotiform knifefish native to a wide range of freshwater habitats in South America. It is the most widespread species of Gymnotus, but it has frequently been confused with several relatives, including some found outside its range like the Central America G. maculosus. The English name "banded knifefish" is sometimes used for the entire genus Gymnotus instead of only the species G. carapo. — Wikipedia (community-edited) |
| Where it lives | Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase |
| Behavior | This species, as with all Gymnotiformes, is an electric fish that has the capability to generate weak electric charges, and then measure the disturbance in the field of electricity created. This system is used for navigation, finding prey and communicating with other G. carapo. They are highly territorial and will react aggressively if detecting the electric field of another individual of their species. — Wikipedia (community-edited) |
| Reproduction | Parental care is provided by the male. The male sits on a depression with its anal fin expanded horizontally guarding a cluster of larvae. More larvae are spread out in leaf litter up to 2 m away. — FishBase |
| Appearance and size | Maximum length 76.0 cm tl male/unsexed; maximum published weight 1.2 kg. — FishBase |
| Biology | Facultative air-breathing; Aggressive. Inhabits turbid slow moving or standing waters. Found also in shallow edges of streams. — FishBase |
Data and studies
The numbers
The numbers
Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.
Typical adult weight
Average adult body mass in each database (FishBase gives the maximum recorded weight).
Adult length
Maximum recorded length. Measured as total length. Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
Water hardness
Minimum tank footprint
Seriously Fish recommends a tank base of at least 71 × 24 in (about 171 US gallons).
Veterinary & husbandry research
Veterinary & husbandry research
- Electrolocation-communication discharges of the fish Gymnotus carapo L. (Gymnotidae: Gymnotiformes) during behavioral sleep Stopa RM et al., Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas 1999
- Reproductive strategies and developmental aspects in mormyrid and gymnotiform fishes Kirschbaum F et al., Journal of physiology, Paris 2002
- Chromatophores and their role in the healing process of the integument of Gymnotus carapo (Teleostei: Gymnotiformes) Blanco Cohene T et al., Journal of molecular histology 2026
Peer-reviewed papers that mention this species alongside captivity, zoos, veterinary care or aquaculture. Some cover several species or mention it only in passing, so check the abstract. 170
Sources for this sheet
- FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
- Seriously Fish species profiles Experienced keeper or breederLong-running aquarium reference written and peer-checked by experienced fishkeepers and ichthyologists; each profile covers habitat, tank size, water, diet, behaviour and breeding.
- Merck Veterinary Manual: Management of aquarium fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Merck Veterinary Manual: Types and features of aquatic systems Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Merck Veterinary Manual: Nutritional diseases of fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
- PubMed (U.S. National Library of Medicine) Peer-reviewed researchIndex of peer-reviewed veterinary, zoo and husbandry research.
- iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.
