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January Tetra – Hemigrammus hyanuary


January Tetra

Tetras are amongst the most popular aquarium fishes. There are probably more than 150 distinct species of tetra from which the aquarist may choose and this includes a large number of visually stunning fishes that are bound to enhance any home aquarium.

Is the January Tetra a good community fish? The January Tetra should be considered to be an excellent community fish and gets on with most species. Being captive-bred it will thrive in a wide range of water chemistry. The January Tetra is suitable for novice aquarists and is relatively easy to breed.

Key Facts

CategoryKey Facts
Common name(s)January Tetra – also known as:
Costello Tetra
Scientific nameHemigrammus hyanuary
FamilyCharacidae
Originate fromCentral and upper Amazon basin through Brazil and Peru in South America
Care requiredEasy to care for and hugely popular
TemperamentPlacid, shoaling fish
Colour & FormPale gold scales with green ittidescence under spine and black caudal peduncle
LifespanUp to 2 years
Adult size1.6 inches
DietOmnivorous – eat aquatic insect larvae in nature
Aquarium size24 inches in length or greater
Compatible withMost other Tetras, Barbs, Danios, Guppies and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches
Avoid keeping withLarge and/or aggressive species
BreedingEasy if you put the fish in the right environment.
Water temp73 – 81 Fahrenheit
Water pH6.0 to 7.2
Water hardness (dGH or dH)1 to 12 dGH

Origins of the January Tetra

Tetras, as a “family” of fishes belonging to the biological family Characidae are found in nature in Africa, Central America and South America.

The January Tetra originates in Lake Hyanuary in Brazil and the species occurs in nature  in the central and upper Amazon basin through Brazil and Peru in South America. “Hyanuary” is anglicised easily as January, hence its common name. The January Tetra is also known as the Costello Tetra and is also wrongly named as the Green Neon – a different species entirely (Paracheirodon simulans).

Characteristics of the January Tetra

As you can see, the January Tetra is an impressive little fish. It has a slender body – often described as being “torpedo-shaped”. It will grow to up to 1.6 inches in the aquarium and lives for only up to two years.

January Tetras prefer fairly soft, acidic water with a pH of 6.0 to 7.2 with a temperature range between 73 and 81 degrees Fahrenheit and up to 12 dGH. 

The January Tetra is a shoaling fish and should be kept as a group of at least six fish, though a shoal of, say, ten or more fish is highly recommended. Having plenty of vegetation to break up lines of sight will also help to protect your January Tetras from predation but it is obviously advised that January Tetras are not kept with predatory species, as they are quite small fish and may be seen as a snack.

The body of the January Tetra is a pale gold with iridescent, pale green reflecting from the scales behind the fill plates along the central, lateral area to the root of the caudal peduncle and the start of the caudal fin, becoming black in colour. The pale gold also bleeds into the caudal and dorsal fins and the other fins are clear (hyaline). 

The January Tetra tends to inhabit the upper area and middle areas of the aquarium (top to bottom). That said, it is a vigorous fish when breeding and will readily traverse the entire aquarium.

The January Tetra is, by nature, a shoaling fish and it is generally recommended to purchase six or more fish, as their nature is to swim together as a shoal and they will tend to thrive much better as a shoal. January Tetras are excellent community fish and are ideal for novice aquarists.

January Tetras, like most rainforest species, much prefer a shaded tank, as they can hide from predation, so consider including floating leaves and/or allowing vegetation to grow so that it floats on the surface of the water to provide shade. They are used to habitats in nature that include decomposing wood and vegetation, which tends to make the water brown (the effects of tannins) and somewhat acidic but seem equally happy in clear water, particularly since you are only likely to obtain captive-bred specimens.

It is generally advised that the minimum tank size for January Tetras should be one of at least 24 inches in length or more due to the shoaling nature of the species, which will enable a small shoal to move around freely. The tank should be well-planted but with clear areas where the fish can swim freely. The water should have gentle movement.

January Tetras are fairly difficult to sex until they are mature, where the female has a slightly fuller body than the male and is also somewhat larger. 

The general rule for Tetras is that by keeping six or more of the same species in an aquarium they will be fully aware of which is male and which is female and they will act accordingly.

Most (but not all) Tetras have an additional fin which identifies them as being Tetras and the January Tetra is no exception. If you look between the dorsal fin and the caudal (tail) fin of the January Tetra you will observe a tiny, additional fin, known as the adipose fin. The purpose of this fin is not fully understood but, if it is present on a freshwater tropical fish then you can be pretty certain that the fish is a Tetra.

Tetra comes from the Greek word “Tetragonopterus” which means square-finned and appears to relate to the four fins on vertical plane of the fish (dorsal, adipose, caudal and anal fins) which span the central line of the fish (when viewed from above or below, front or rear) and are not present as a pair (e.g. the pectoral or pelvic fins).

January Tetra – Video

How do January Tetras breed?

Tetras, in general, will scatter eggs by laying them over fine plants such as Cabomba, Fontanalis or Java Moss.

January Tetras, like most species, are noted to leap above the water surface during breeding and in general, so it is advised that the tank should be covered to mitigate the risk of losing fish.

As the female January Tetra becomes ripe with eggs, the difference between the sexes may become more evident, as the body expands because it is carrying eggs. If you plan to attempt to breed January Tetras then it is recommended that you have a breeding tank prepared. Such a tank can be empty but you may wish to include a mesh or grid under which the fertilized eggs will fall and/or a sterilized breeding mop.

That said, January Tetras may breed in a community tank and, if the tank is well planted, it is possible that at least a few fry may survive to reach adulthood. Having a good covering of Willow Moss on the floor of the aquarium seems to provide a safe haven for fry, which can help them to survive predation in a community or single-species tank.

Some say that a novice may find it difficult to breed January Tetras but, in my experience, by understanding the conditions that are ideal for breeding, most species will breed quite readily, as it is natural for them so to do and, in general, nature will find a way.

The female will swim more vigorously around the tank and, if you include two males then they will encourage her to lay her eggs by bumping into her. She will lay her slightly adhesive eggs which will immediately be fertilized by the male(s) and will either stick to plants or spawning mop or will fall to the bottom of the tank (preferably through the mesh or trap). Once spawning is complete, remove the adults, as they are likely to consume the eggs, given the chance, and take no further parental responsibility.

Spawning usually takes place in the early morning. 

Breeding tank for January Tetras

You should prepare a tank of around 10 gallons in size with mature, soft, acidic water. The water should have a low level of light.

You may wish to introduce mosquito larvae or bloodworm as an inducement to reproduction.

The female will swim amongst the plants, laying around 200 eggs during a spawning. The male(s) will swim alongside or behind her and fertilize the eggs as they are laid. Once the female has laid all her eggs the adults should be removed from the breeding tank.

Keep the lights off and the tank dark because Tetra eggs and fry are particularly sensitive to the light.

The eggs will hatch typically in a day or two depending on tank temperature and conditions and the fry will become free-swimming after around three to four days after hatching. Keep the tank unlit for the first week or so then gradually increase the lighting.

The newly hatched fry will firstly feed on their yolk sac but, once free-swimming, can be fed infusoria (particularly rotifers) and will also thrive on egg yolk during the first two to four weeks. It is worth mentioning that immediately after hatching, fry seem quite vigorous but will soon go into a resting state before they become free-swimming so please don’t mistake this initial stage as being free-swimming.

After around four days or so add baby brine shrimp. Once the fry are sufficient in size not to be treated as a snack then they can be introduced into the community tank where they will join the existing shoal. Before moving the adolescent fish into the community tank ensure that you have balanced the water temperatures to mitigate the risk of White Spot or other diseases being triggered.

Should your January Tetras have a special diet for breeding?

Adult January Tetras don’t need any particular inducement to breed. That said, it has been suggested that adding mosquito larva may encourage them, presumably because the addition of a new food may “fool” the fish into thinking that it is breeding time. From my own experience, I would always recommend keeping all of your fish in the best possible condition at all times, as this is good for the wellbeing of your fish.

Mike Wheeler

I started keeping freshwater tropical fish in 1972 and it has been something of a passion ever since. In this website, my aim is to build up an everyman's guide to help the everyday aquarist get the best from this inspiring and entertaining hobby.

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