Reed tetra
Hyphessobrycon elachys
A micro-tetra from the Paraguay basin with a large black spot at the tail base and golden reflections on a translucent body — delicate and fascinating. Also known as 'Kitty Tetra' for its rounded snout. At just 1.5–2.5 cm adult size, it is perfect for planted nano tanks with South American dark-water biotope. In nature it inhabits shallow, slow, tannin-rich waters with dense vegetation. In groups of 10+ it becomes confident and active; in groups that are too small it hides. Suitable for tanks with dwarf shrimp.
Water Temperature
22 - 27 °C
pH Value
6 - 7.5
Water type
Freshwater
Tank level
Middle
Adult size
2.5 cm
Minimum tank volume
>= 40 L
Minimum group
>= 8
GH
1 - 12 dGH
KH
1 - 6 dKH
TDS
25 - 240 ppm
Conductivity
39 - 375 uS/cm
Species description
Geographical Origin and Habitat: Rio Paraguay (Pantanal area). Lives in marshy lagoons with very shallow waters, suffocated by water lilies and submerged meadows, with no flow.
Taxonomy and Morphology: Dwarf Blue Tetra / False Dawn Tetra (Hyphessobrycon elachys). Tiny cyprinid (Nano-fish). Often confused with Aphyocharax rathbuni (much more robust). Very slender fry-like body.
Social Behavior: Quiet, shy and absolutely gregarious (Schools of 10-15 elements). Males challenge each other by excessively widening their small anal and dorsal fins (Jerky dancers).
Coloration and Sexual Dimorphism: Silvery livery with incredible "metallic blue-purple" shades when hit by light, with an oblong black spot at the base of the tail and pointed anal and dorsal fin (males only). Females are bare.
Care, breeding and tankmates
Aquarium Setup: Tank for Nano-Fish (50-60 cm / 20-24 inches). Bottom of leaves (Catappa/Oak), intricate twigs, ultra-shielded light from floating plants (Limnobium or Pistia). Without surface cover they panic and hide.
Diet and Feeding: Pure micro-predators. Very high quality freeze-dried or powdered feeds. The ideal are cyclops and microworms; if fed large flakes they simply will not eat (mouth too small).
Water Quality: Extremely sensitive to pollutant peaks. Pantanal water requires slight seasonal thermal fluctuations (22°C / 72°F in winter, 26°C / 79°F in summer). They need very gentle filtration without powerful water jets.
Compatibility and Cohabitation: Corydoras hastatus (same colors) lives in nature in mixed flocks with H. elachys (Batesian mimicry): putting them together is mandatory for a perfect biotope. Also excellent with Neocaridinas (they do not touch the young).
Aquarium Breeding: Very elusive. They hide microscopic transparent eggs on moss threads or weak roots. Without ready infusoria (paramecia) the brood of microscopic fry starves to death in 48 hours.
Risks and Diseases: Predation! Their size (2 cm / 0.8 inches and thin body) makes them an irresistible "spaghetti" even for 5 cm (2 inch) fish. They risk being decimated by Bettas and even by large Platies.
Geographic Origin and Distribution
Rio Paraguay (Pantanal area). Lives in marshy lagoons with very shallow waters, suffocated by water lilies and submerged meadows, with no flow.
Origin
Extra-Amazon South AmericaEast Asia
Fish profile
- Temperament
- Peaceful
- This is a highly peaceful and somewhat shy species that thrives in a calm environment. They are a schooling fish that relies on the presence of conspecifics to feel safe and exhibit their best behavior. When kept in sufficiently large groups, they are active and inquisitive without ever bothering tank mates.
- Diet
- Omnivore
- These are omnivorous micro-predators in the wild, feeding on tiny invertebrates and zooplankton. In the aquarium, they readily accept crushed high-quality flake foods and micro-pellets. Supplementing their diet with live or frozen foods like Daphnia will enhance their coloration.
- Life expectancy
- 3-4 years
- This species has a relatively short life cycle in captivity, typically ending between 3 and 4 years under impeccable maintenance. Impeccable tank hygiene and thermal stability are decisive factors in allowing this fragile fish to reach its maximum age limit. A poorly maintained environment can cause a rapid decline in their general physical condition.
- Adult size
- 2.5 cm
- The catalog's scalar value is 2.5 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 2 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Hyphessobrycon elachys (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
- Maintaining a proper sex ratio is less critical for this species compared to some others, as they are a schooling fish. Keeping them in groups of at least eight to ten individuals ensures natural behavior and reduces stress. Having a mix of males and females can help diffuse any minor squabbles among displaying males.
- Feeding frequency
- Twice daily
- These active fish benefit from multiple small feedings throughout the day rather than one large meal. Feeding them two to three times daily with amounts they can consume in under two minutes is ideal. This schedule helps prevent bloating and keeps water parameters stable by reducing uneaten food.
- Bioload
- Low
- This species produces a very minimal bioload due to its small physical size. It is highly suitable for smaller aquariums or heavily planted setups. However, standard filtration and regular water changes remain essential.
- Flow
- Weak
- Originating from slow-moving tributaries and forested pools, they prefer gentle to moderate water currents. High flow environments can quickly exhaust these fish and cause them significant stress. A sponge filter or a baffled hang-on-back filter provides the perfect amount of water movement.
- Jump risk
- No
- Reproduction
- Oviparous
- They are egg scatterers that do not provide any parental care to their offspring after spawning. To encourage breeding, a separate tank with soft, slightly acidic water and fine-leaved plants is required. Once eggs are laid and fertilized, the adult fish must be removed promptly to prevent them from eating the eggs.
- Compatibility & tankmates
- Peaceful
- This species is exceptionally peaceful and does well in community tanks with other small, non-aggressive fish. They should never be kept with large or boisterous species that might view them as food. Ideal tank mates include small rasboras, Corydoras catfish, and peaceful dwarf cichlids.
- Tank level
- Middle
- This species primarily occupies the middle region of the aquarium water column during normal activities. They are active swimmers that appreciate ample open swimming space in the center of the tank. They will frequently dart in and out of plant thickets or hardscape for cover when resting.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3 ± 0.3 se
- Resilience
- High (less than 15 months)
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.01202, 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.
