January tetra
Hemigrammus hyanuary
An elegant but underrated Amazonian tetra: a yellow-green iridescent stripe runs along the body from snout to caudal peduncle, above a thin black band — creating a unique natural light effect. Named after Lake Hyanuary near Manaus where it was discovered. The eye iris is bright green, a distinctive detail. Peculiarity: wild specimens sometimes show a golden sheen caused by a parasite in the natural biotope, absent in captive-bred specimens. Ideal for dark-water Amazonian biotopes with leaves, driftwood and tannins.
Wassertemperatur
22 - 27 °C
pH-Wert
6 - 7.5
Wassertyp
Süßwasser
Tankfüllstand
Oberfläche und Mitte
Erwachsenengröße
4 cm
Mindesttankvolumen
>= 40 L
Mindestgruppe
>= 6
GH
2 - 12 dGH
KH
1 - 6 dKH
TDS
40 - 240 ppm
Leitfähigkeit
63 - 375 uS/cm
Artbeschreibung
Geographical Origin and Habitat: Amazon River basin, especially near Lake Hyanuary (hence the name). Populates flooded forests and calm lowland basins rich in submerged obstacles and vegetation.
Taxonomy and Morphology: Costello Tetra / Green Neon Tetra (Hemigrammus hyanuary). Small cyprinid with a lozenge profile, slightly "taller" than its cousins. It has the typical black spot of the genus Hemigrammus located on the root of the tail.
Social Behavior: Gregarious (needs 6 to 10 individuals) and shy. In bare tanks it is prone to panic attacks; actively explores only if it feels shielded by nearby plant beds (edge effect).
Coloration and Sexual Dimorphism: Underrated: olive/golden body crossed by a bright golden/green horizontal line that ends in the caudal peduncle with a sharp black "eye" bordered with upper yellow-gold. Females noticeably swollen on the abdomen.
Pflege, Zucht und Mitbewohner
Aquarium Setup: The emblem of the planted aquarium fish. Color contrast is obtained only by offering densely planted backgrounds or the shade of a large Anubias/Echinodorus, using dark backgrounds and non-turbulent waters.
Diet and Feeding: Surface insectivore and omnivore. Equipped with a slightly upward-facing mouth, preys on springtails, mosquitoes and in the aquarium attacks slow-sinking flakes. Never let them lack freeze-dried brine shrimp (rich in carotenes).
Water Quality: Strong tolerance to neutral ranges. Resists very well to GH hardness close to 10 or 12, as long as it does not suffer sudden temperature increases over 28 degrees (82°F), where it suffers from lack of oxygen.
Compatibility and Cohabitation: Perfect for Dutch aquariums in community with delicate fish (Microdevario, small Badis, Corydoras pygmaeus). Discard explosive cohabitations like Clown Loaches or large barbs that would cause lethal fading in the Costello Tetra.
Aquarium Breeding: Lays eggs in pairs (although not monogamous) in the half-light of the moss at dawn, tiny eggs (Egg scatterer). Requires darkness and very pure water to avoid fungal attacks on the laid caviar.
Risks and Diseases: Rarely available fish, unfortunately replaced in community tanks by more "commercial" species. Suffers from white spot disease (Ich) following drastic temperature changes.
Geografische Herkunft und Verbreitung
Amazon River basin, especially near Lake Hyanuary (hence the name). Populates flooded forests and calm lowland basins rich in submerged obstacles and vegetation.
Ursprung
Amazonas, Orinoco und Guayana
Fischprofil
- Temperament
- Peaceful
- They are exceptionally peaceful and somewhat shy, requiring a large school of at least six individuals to feel secure. When kept in smaller numbers, they may become stressed, lose their vibrant colors, and hide continuously. A proper schooling environment encourages their natural, confident behaviors and tight grouping dynamics.
- Diät
- Omnivore
- In the wild, they are micro-predators feeding on small insects, worms, and crustaceans. In the aquarium, they readily accept high-quality crushed flakes, micro-pellets, and freeze-dried foods. Supplementing their diet with live or frozen foods like daphnia, baby brine shrimp, and bloodworms will enhance their coloration and vitality.
- Lebenserwartung
- 3-5 years
- Erwachsenengröße
- 4 cm
- Geschlechterverhältnis
- School
- Keeping a balanced ratio or a slight majority of females is generally recommended to prevent males from constantly harassing a single female. In a large enough school, the sex ratio becomes less critical as aggression is dispersed. A larger group naturally forms a healthy hierarchy, minimizing any stress related to breeding behavior.
- Fütterungsfrequenz
- Twice daily
- It is highly recommended to feed them two to three small meals a day rather than one large one. Offering only what they can consume within a couple of minutes ensures minimal food waste and prevents water quality degradation. Frequent, small feedings closely mimic their natural foraging behavior in the wild.
- Bioload
- Low
- These small tetras produce a minimal bioload, making them excellent candidates for smaller or heavily planted aquariums. They do not generate significant amounts of waste compared to larger species, reducing the burden on the filtration system. However, keeping them in large schools will naturally increase the overall waste output, requiring adequate biological filtration.
- Fluss
- Strong
- They prefer a moderate to low water flow that simulates the slow-moving tributaries and flooded forest regions of their natural habitat. Strong currents can exhaust these small fish and cause them significant stress over time. Providing areas of still water, particularly near dense vegetation, allows them places to rest comfortably.
- Sprungrisiko
- No
- Reproduktion
- Oviparous
- Breeding these tetras can be challenging as they are egg-scatterers that provide no parental care. They require soft, acidic water and dim lighting to trigger spawning behavior successfully. A separate breeding tank with fine-leaved plants or a spawning mop is necessary, and parents must be removed immediately after laying eggs to prevent predation.
- Kompatibilität & Tankkameraden
- Peaceful
- This species is incredibly peaceful and thrives in a community setup with other similarly sized, non-aggressive fish. Excellent tank mates include small rasboras, Corydoras catfish, and peaceful dwarf cichlids. They should never be kept with large or aggressive species that might view them as prey or cause them undue stress.
- Tankfüllstand
- Top/Middle
- These fish primarily occupy the middle to upper levels of the water column in the aquarium. They are active swimmers that appreciate ample open swimming space combined with areas of dense planting. While they occasionally dart to the surface for food or explore the bottom, they will spend most of their time cruising the midwater.
Wissenschaftliche Modelle & Parameter
FishBase
Zugang zu den offiziellen wissenschaftlichen Daten der Art
FishBase v25.04Daten synchronisiert am: 15.06.2026
- Trophäenniveau
- 3,2 ± 0,4 se
- Belastbarkeit
- Hoch (weniger als 15 Monate)
- Phylogenetische Einzigartigkeit (PD50)
- 0.5
- Bayessche Längen-Gewichts-Beziehung
- a = 0.01259, b = 3.05
- AnfälligkeitGeringe Anfälligkeit (10 / 100)
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