FishFreshwaterExpert
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Gold-lined Knifefish / Longtail
Sternopygus macrurus
A giant, elegant nocturnal hunter reaching 60+ cm. Draped in dark velvet with a stunning, razor-sharp golden line running down its body. Massive, highly predatory, and utterly intolerant of other knifefishes. A stunning centerpiece for Jumbo tanks.
Water Temperature
22 - 28 °C
pH Value
6 - 7.5
Water type
Freshwater
Tank level
Bottom
Adult size
45 cm
Minimum tank volume
>= 500 L
Minimum group
>= 1
GH
5 - 15 dGH
KH
2 - 7 dKH
TDS
95 - 295 ppm
Conductivity
148 - 461 uS/cm
Species description
Geographical Origin and Habitat: Continent-wide distribution across the Amazon, Orinoco, and upper Paraná systems. Strictly benthic, lurking heavily camouflaged among dense sunken roots, mudbanks, and flooded forests in mid-to-large rivers.
Taxonomy and Morphology: A true giant of the Sternopygidae family (related to the tiny Glass Knifefish). Growth is relentless: reaches 50-60 cm (20-24 inches) in aquaria, sometimes larger in the wild. Very thick, muscular body compared to the razor-thin smaller knives. Lacks dorsal and caudal fins; the tail tapers off into an exceptionally long, thin 'whip' (hence macrurus or longtail). Navigates and hunts using a continuous weak electrical pulse (electrolocation).
Social Behavior: Purely nocturnal and highly benthic. Very shy as a juvenile, hiding all day, but becomes much bolder as a massive adult, dominating the tank floor at night. Its behavior changes as it matures: from tolerant to SAVAGELY AGGRESSIVE toward its own kind or other knifefish species. Electrical interference causes pure rage, resulting in biting and torn flesh until the weaker fish dies.
Coloration and Sexual Dimorphism: Subtle but breathtaking. The laterally compressed body is a dark, matte olive-black or brown velvet. The signature mark is a vivid, striking gold or creamy-white line tracing perfectly horizontally from the gills straight to the tip of the tail. Usually sports a large, black, white-rimmed 'eye-spot' behind the gills. Females are thicker in the abdomen.
Care, breeding and tankmates
Aquarium Setup: A true half-meter monster requiring a MASSIVE tank (minimum 200 cm / 6-7 feet length). A FINE SAND substrate is mandatory—they lack protective scales and will quickly develop fatal flesh-eating fungal infections if housed over sharp gravel or rough lava rocks. You MUST provide an opaque, dark PVC pipe or a massive hollow stump for it to retreat into during daylight hours. Dimly lit tanks prevent psychological stress.
Diet and Feeding: Nocturnal Carnivore. Voracious appetite as an adult. Feed substantial, meaty items using tongs directly near its cave at dusk: whole thawed shrimp (shell removed), mussels, jumbo earthworms, and smelt (silversides). Easily trained onto massive, sinking carnivore pellets. Will completely ignore all vegetable matter. Any small or sleeping fish will be eaten during the night.
Water Quality: Extremely vulnerable to tank chemistry due to its 'naked' skin. Copper medications, malachite green, and formalin will kill it rapidly. Requires pristine water via massive biological filtration. pH 6.0-7.5. Temp 23-28°C (73-82°F). Gentle bottom current preferred.
Compatibility and Cohabitation: MUST BE KEPT AS A SOLITARY KNIFEFISH. Zero tolerance for conspecifics or other electric fish. Best housed in peaceful 'Monster Fish' setups: large Oscars, Uaru, Severums, giant armored Plecos, or Freshwater Stingrays. It will systematically hunt down and swallow small/medium fish (Tetras, Corydoras) in the dark.
Aquarium Breeding: Undocumented in the hobby due to the sheer violence of keeping two adults together in confined volumes.
Risks and Diseases: 1. LETHAL RADAR WARS: Keeping two adults in the same tank guarantees a fight to the death due to electrical jamming. 2. Fatal chemical burns from cheap, copper-based aquarium medications. 3. Fungal/Bacterial ulcerations of the belly from rough substrates.
Geographic Origin and Distribution
Continent-wide distribution across the Amazon, Orinoco, and upper Paraná systems. Strictly benthic, lurking heavily camouflaged among dense sunken roots, mudbanks, and flooded forests in mid-to-large rivers.
Origin
Amazon, Orinoco, and GuianasNorth America
Fish profile
- Temperament
- Semi-aggressive
- The overall temperament of the Ghost Knifefish can be best described as shy but predatory. Their disposition makes them a unique addition to the appropriate aquatic community, provided their specific needs are respected. Stressful conditions, such as poor water quality or overcrowding, can drastically alter their typical behavioral patterns. A quiet environment and a stable routine will bring out the most confident and engaging personality from this species.
- Diet
- Omnivore
- Feeding the Ghost Knifefish properly requires acknowledging its natural role as a carnivorous. A staple diet of premium flakes or pellets should be supplemented with nutrient-rich treats to replicate natural foraging. It is advisable to soak dry foods beforehand to prevent digestive issues and swim bladder complications. Consistently offering a diverse menu will significantly boost their immune system and overall vitality.
- Life expectancy
- 10-15 years
- This knifefish has a very long lifespan, which in captivity can exceed 10 to 15 years when housed in a suitable and well-cared-for environment. Stability of chemical and physical parameters and a rich, clean diet prevent health issues and skin infections. Since it is a species that reaches large sizes, available space is an essential element to guarantee its longevity.
- Adult size
- 45 cm
- The catalog's scalar value is 45 cm. The FishBase species summary source reports a maximum adult measurement of 141 cm for this species, recorded as total length (TL). The taxonomic record consulted is Sternopygus macrurus (live-2026-07-30); 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.
- Sex ratio
- Specific M:F ratio
- To prevent undue stress, it is recommended to keep the Ghost Knifefish in a carefully managed sex ratio. Providing more females than males reduces the constant harassment that a single female might endure. If keeping multiple males, the aquarium must be sufficiently large to allow for the establishment of distinct territories. Careful observation during the first few weeks will dictate if any aggressive individuals need to be rehomed.
- Feeding frequency
- Twice daily
- To mimic its natural foraging behavior, the Ghost Knifefish should be fed small portions two to three times a day. Overfeeding can lead to severe health issues and quickly degrade the water quality. It is crucial to only provide an amount of food that the fish can consume within a few minutes. Adjusting the feeding frequency based on the fish's age and activity level is a best practice for long-term care.
- Bioload
- Maintaining this freshwater species requires understanding its high bioload profile. The Ghost Knifefish will thrive when the filtration system is carefully matched to its specific waste production. Frequent testing of the water chemistry is highly recommended to ensure no dangerous spikes occur. Excellent water quality is the foundation for preventing disease and promoting a vibrant, active fish.
- Flow
- Stagnant
- In terms of water movement, the Ghost Knifefish thrives best in environments with moderate flow. Replicating the hydrodynamic conditions of their native habitat is key to reducing stress and promoting natural behaviors. Powerheads or spray bars can be strategically placed to create adequate currents without overwhelming the fish. Careful placement of hardscape and plants can also provide sheltered resting zones away from the main flow.
- Reproduction
- Oviparous
- The reproductive strategy of the Ghost Knifefish involves being a egg scatterer. Breeding this species in captivity can be a rewarding challenge that requires dedicated conditioning of the broodstock. Specific triggers such as changes in temperature, diet, or water chemistry are often necessary to induce spawning. Once breeding occurs, specialized care for the fry, including appropriately sized live foods, is critical for their survival and development.
- Compatibility & tankmates
- The Ghost Knifefish is known to be will eat small fish, keep with peaceful large species when integrated into a carefully planned setup. They tend to exhibit the best colors and natural behaviors when kept with species of a similar temperament. Aquarists must be cautious to provide enough visual barriers if housing them with semi-aggressive tankmates. Overall, a well-thought-out stocking plan will yield a beautiful, drama-free aquatic display.
- Tank level
- Bottom
- This species is predominantly a bottom to mid dweller within the aquarium setup. Providing the appropriate spatial layout with open swimming areas or dense vegetation where they feel secure is highly beneficial. By understanding their preferred depth, aquarists can carefully select complementary species that occupy other regions of the tank. This spatial separation helps to reduce competition for food and minimizes unnecessary territorial disputes.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3.2 ± 0.4 se
- Phylogenetic uniqueness (PD50)
- 0.501
- Bayesian Length-Weight
- a = 0.00309, b = 2.84
- VulnerabilityVery high vulnerability (84 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
Related species
Recommendations grouped by close relatives, companion choices, and similar care.
