January tetra
Hemigrammus hyanuary
Also known as costello tetra
Care at a glance
- Temperature
- 73–81°F (23–27°C)
- pH
- 5.5–7.0
- Adult size
- 1.6 in (4 cm)
- Minimum tank
- 17 gal (65 L)
- Temperament
- Peaceful
- Social behavior
- Schooling
- Swim level
- Middle
- Difficulty
- Medium
- Breeding
- Hard
- Rarity
- Rare
- Origin
- Peru, Brazil
- Family
- Characidae
Overview
Keep a school of six or more in a tank around 65 liters and they will hold the middle to upper water. They are peaceful and active, and a proper group keeps them calm and colored up. Feed small flake, micro-pellets, and the occasional frozen brine shrimp or daphnia. They suit a planted soft-water community alongside other small, gentle fish.
In the wild
The January tetra comes from calm, shallow Amazon waters in Peru and Brazil, including the Lago do Januari area near Manaus that gives it its name. These are soft, slightly acidic, shaded spots over sand or mud, rich in plants and biofilm. Match that with a dim, well-planted tank, soft water, and a pH from the mid 5s to about 7. Botanicals and a darker substrate help show off the fish.
Good to know
Hemigrammus hyanuary is a characin (family Characidae) reaching roughly 4 cm. It has a slim, silvery body with a dark stripe and a small gold or green mark near the tail. It is an egg scatterer that gives no parental care, with eggs hatching in about a day to a day and a half. It is listed as Least Concern with stable wild numbers.
Did you know
Despite the wintry English name, it has nothing to do with the season. "January" is just an anglicized take on Januari, the Brazilian lake near where the fish was found.
Where to buy
Some links may not be the exact species or variety.
…or ask your local fish store.
Appears in
Keeping January tetra?
Track water tests, reminders and stocking fit.
Related species

Glowlight tetra
Hemigrammus erythrozonus1.6 in (4 cm)18 gal (70 L)75–82°F (24–28°C)
Garnet tetra
Hemigrammus pulcher1.8 in (4.5 cm)20 gal (75 L)73–82°F (23–28°C)
Head-and-taillight tetra
Hemigrammus ocellifer1.8 in (4.5 cm)17 gal (65 L)75–82°F (24–28°C)
Rummy-nose tetra
Hemigrammus rhodostomus2 in (5 cm)20 gal (75 L)75–81°F (24–27°C)
Golden Tetra
Hemigrammus rodwayi2.2 in (5.5 cm)20 gal (75 L)75–82°F (24–28°C)
Red flush tetra
Hemigrammus stictus2.4 in (6 cm)20 gal (75 L)73–81°F (23–27°C)
