Giant Hatchetfish
Thoracocharax securis
The 'Leviathan' of the hatchetfish family. An enormous, heavily armored silver top-dweller reaching 9 cm. Magnificent in massive schools alongside big South American cichlids, but fragile and notoriously difficult to acclimate from the wild.
Water Temperature
24 - 28 °C
pH Value
6 - 7.5
Water type
Freshwater
Tank level
Surface
Adult size
7 cm
Minimum tank volume
>= 60 L
Minimum group
>= 1
GH
2 - 15 dGH
KH
1 - 7 dKH
TDS
40 - 295 ppm
Conductivity
63 - 461 uS/cm
Species description
Geographical Origin and Habitat: Vast distribution across the main Amazon River system in Brazil and Peru. Prefers expansive, quiet lagoons, flooded oxbows, and slow rivers, schooling under the thick canopy of coastal trees and fallen wood.
Taxonomy and Morphology: The absolute giant of the Gasteropelecidae family. Thoracocharax (meaning 'armored characin') easily reaches 8-9 cm (3.5 inches). The abdominal keel is so deep and massive it almost looks unnatural, comprising the vast majority of the fish's profile. Exceptionally long pectoral 'wings'.
Social Behavior: Highly gregarious, schooling placidly right at the surface. Less prone to panic than dwarf species, but when they do jump, their massive flight muscles produce explosive, loud ballistic jumps that carry them meters away in the wild. Becomes deeply depressed and if kept in small numbers.
Coloration and Sexual Dimorphism: Brilliant, mirror-like platinum/silver base. The scales are large and heavily outlined, granting an 'armored' appearance. Subtle yellow tinges on the flat back and at the base of the massive pectoral fins. No clear sexual dimorphism besides gravid females being slightly rounder.
Care, breeding and tankmates
Aquarium Setup: Demands MASSIVE volumes. A proper school requires a minimum 150 cm (5 feet) long tank. A HEAVY, COMPLETELY SEALED LID IS NON-NEGOTIABLE. Additionally, you MUST leave a 4-6 inch (10-15 cm) air gap between the water and the lid/lights; otherwise, these giants will launch into the glass at high speed, snapping their spines instantly. Copious broad-leaf floating plants are required.
Diet and Feeding: Extreme macro-insectivore. Has a massive appetite. Feed large freeze-dried insects (crickets, mealworms), jumbo floating pellets, and copious amounts of floating frozen bloodworms and krill chunks. Will starve if forced to dive for food; ignores sinking items completely.
Water Quality: THE PRIMARY CHALLENGE. Almost exclusively wild-caught, suffering heavy losses during shipping. Requires pristine, highly oxygenated water with minimal surface chop. pH 6.0-7.0, soft to medium GH. Temp 24-28°C (75-82°F). Zero tolerance for ammonia, which causes rapid fin corrosion on their 'wings'.
Compatibility and Cohabitation: Their sheer size allows them to be the perfect top-dweller for tanks housing jumbo South American peaceful cichlids: adult Discus, Geophagus, Uaru, Severums, and giant Plecos. Do NOT house with aggressive, toothy cichlids (Oscars, Jaguars) or Arowanas that will shred or eat them. Absolute minimum school of 6, ideally 10+.
Aquarium Breeding: Essentially unknown in the home aquarium; breeds during massive natural flood cycles.
Risks and Diseases: 1. LETHAL ACCLIMATION. Over 50% often die from Ich, internal parasites, and shipping stress in the first month unless strictly quarantined. 2. Ballistic suicide against the tank lid. 3. Starvation if water flow pulls food below the surface too quickly.
Geographic Origin and Distribution
Vast distribution across the main Amazon River system in Brazil and Peru. Prefers expansive, quiet lagoons, flooded oxbows, and slow rivers, schooling under the thick canopy of coastal trees and fallen wood.
Origin
Amazon, Orinoco, and Guianas
Fish profile
- Temperament
- Semi-aggressive
- They are peaceful, skittish, and highly specialized fish that require a calm environment. They are easily frightened by sudden movements, loud noises, or aggressive tank mates. Despite their delicate nature, a large school of Giant hatchetfish is a stunning display.
- Diet
- Omnivore
- They are strict surface-feeding insectivores whose natural diet consists almost entirely of insects. In captivity, they require floating foods, as they will completely ignore anything that sinks. High-quality floating flakes and live fruit flies provide an excellent and natural food source.
- Life expectancy
- 3-5 years
- Thoracocharax securis has an average lifespan in the aquarium of about 3 to 5 years when managed with proper care. To ensure it reaches this age, it is essential to have an aquarium with a tight-fitting cover to prevent fatal jumps out of the water. Stable parameters, well-filtered water, and a lack of pollutants are vital to protect its delicate skin from bacterial infections. Proper and balanced nutrition plays an equally important role in supporting its overall longevity.
- Adult size
- 7 cm
- The catalog's scalar value is 7 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 6.8 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Thoracocharax securis (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.
- Sex ratio
- School
- Distinguishing between the sexes is very difficult, though females may appear slightly wider when full of eggs. They are obligate schooling fish and must be kept in groups of at least six, preferably ten or more. Keeping them in small numbers will result in severe stress.
- Feeding frequency
- Twice daily
- They should be fed small amounts two to three times daily. Because they only eat from the surface, it is crucial to monitor feedings to ensure the food does not sink and go to waste. Care must be taken to ensure bottom-dwelling fish do not steal their food.
- Bioload
- The Giant hatchetfish produces a low to moderate bioload, suitable for well-maintained community aquariums. Because they require pristine water conditions, excellent filtration and regular water changes are mandatory. A mature, stable aquarium environment is necessary before introducing these delicate fish.
- Flow
- Stagnant
- They prefer gentle to moderate water flow, mimicking the calm streams of South America. Strong surface agitation or heavy currents will stress them and make it difficult for them to feed naturally. The use of a spray bar can help distribute the filter return evenly.
- Reproduction
- Oviparous
- Breeding the Giant hatchetfish in captivity is considered extremely difficult and rarely achieved. They are egg scatterers that deposit their eggs among floating plant roots in very soft, acidic water. Triggering the spawn often requires simulating the rainy season with large water changes.
- Compatibility & tankmates
- They are incredibly peaceful and make wonderful additions to calm community aquariums. They should be housed with other peaceful, slow-moving fish such as small tetras and bottom-dwelling catfish. They must never be kept with aggressive, boisterous, or fin-nipping species that will cause stress.
- Tank level
- Top
- They are obligate surface dwellers that spend their entire lives within the top few inches of the water column. Their upturned mouths and flat dorsal profiles are perfectly adapted for skimming the surface. Floating plants are highly appreciated, providing them with cover.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3.5 ± 0.4 se
- Phylogenetic uniqueness (PD50)
- 0.752
- Bayesian Length-Weight
- a = 0.01698, b = 3.09
- VulnerabilityLow vulnerability (10 / 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.
