Actinopteri (ray-finned fishes) > Gymnotiformes
(Knifefishes) > Gymnotidae
(Naked-back knifefishes) > Gymnotinae
Etymology: Gymnotus: Greek, gymnos = naked (Ref. 45335).
More on author: Linnaeus.
Environment: milieu / climate zone / depth range / distribution range
Freshwater; benthopelagic; pH range: 6.0 - 7.5; dH range: ? - 15; potamodromous (Ref. 51243). Subtropical; 22°C - 28°C (Ref. 1672)
Central and South America: southern Mexico to Paraguay, including Trinidad.
Length at first maturity / Size / Weight / Age
Maturity: Lm 19.4, range 25 - ? cm
Max length : 76.0 cm TL male/unsexed; (Ref. 79585); max. published weight: 1.2 kg (Ref. 79585)
Aggressive (Ref. 27188). Inhabits turbid slow moving or standing waters (Ref. 11225). Found also in shallow edges of streams (Ref. 75964). Can survive when ditches, canals and small ponds dry out. (Ref. 11225). Feeds mainly at night on worms, insects (e.g. odonate larvae), shrimps, fish (preferably small characids, e.g. Ctenobrycon and Curimata) and plant matter (Ref. 7020; 10011). Oviparous (Ref. 205). Mouth brooding by males is observed in this species (Ref. 55570). Males provide parental care in nests excavated for eggs and larvae (Ref. 55570). Uses its long anal fin for locomotion. Can distinguish between a `friendly neighbor' and a potentially `threatening stranger' based on electric organ discharge (EOD) waveform alone (Ref. 10011). Relationship between EOD pattern and agonistic behavior in this species has been demonstrated (Refs. 10531, 10532, 10533). Shows auditory abilities, responding best to a frequency of 1000 Hz, with an upper limit above 5000 Hz (Ref. 10831). Also responds to vibratory stimuli (water waves: 125-250 Hz) with transient increase in EOD rate (Ref. 10834). 'Prefers' temperatures of 24-25°C (Ref. 10836).
Life cycle and mating behavior
Maturity | Reproduction | Spawning | Eggs | Fecundity | Larvae
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 (Ref. 55570).
Campos-da-Paz, R., 2003. Gymnotidae (Naked-back knifefishes). p. 483-486. In R.E. Reis, S.O. Kullander and C.J. Ferraris, Jr. (eds.) Checklist of the Freshwater Fishes of South and Central America. Porto Alegre EDIPUCRS, Brasil. (Ref. 36692)
IUCN Red List Status (Ref. 125652)
Threat to humans
Fisheries: of no interest; aquarium: commercial
Estimates based on models
Phylogenetic diversity index (Ref. 82805
= 0.5000 [Uniqueness, from 0.5 = low to 2.0 = high].
Bayesian length-weight: a=0.00355 (0.00268 - 0.00470), b=2.95 (2.87 - 3.03), in cm total length, based on LWR estimates for this species (Ref. 93245
Trophic level (Ref. 69278
): 3.6 ±0.56 se; based on food items.
Generation time: 3.6 ( na - na) years. Estimated as median ln(3)/K based on 2 growth studies.
Resilience (Ref. 120179
): Medium, minimum population doubling time 1.4 - 4.4 years (tm=2).
Fishing Vulnerability (Ref. 59153
): Moderate vulnerability (37 of 100) .
Climate Vulnerability (Ref. 125649
): (0 of 100) .
Nutrients (Ref. 124155
): Calcium = 92 [50, 174] mg/100g ; Iron = 1.53 [0.95, 2.42] mg/100g ; Protein = 17.9 [16.8, 19.0] % ; Omega3 = 0.316 [0.147, 0.664] g/100g ; Selenium = 39 [17, 94] μg/100g ; VitaminA = 15.9 [5.3, 47.1] μg/100g ; Zinc = 1.28 [0.89, 1.85] mg/100g (wet weight);