Rainbowfish care

Rainbowfish color up as they mature and settle, so a drab young fish in a shop often becomes a shimmering adult in a good group. The larger melanotaenias want room to swim, while blue-eyes and threadfins stay small enough for a nano tank. Each profile lists tank size, water conditions and group size.

Tank size: 11–66 gal; 11 gal (40 L) to 66 gal (250 L); half the list needs 29 gal (110 L) or more
Temperature: 75–84°F; 24–29°C, most of the list
pH: 6.8–8.0; Most of the list
Difficulty: 17 easy; 47 medium · 1 difficult
Temperament: 62 peaceful; 3 mostly peaceful

65 species

Rainbowfish care

Rainbowfish are schooling fish and show their colour in a group: six is the minimum, more is better, and several males per species is what turns on the display. They are active open-water swimmers, so tank length matters more than volume; the 4 to 6 inch (10 to 15 cm) melanotaenias want a 4 foot tank, which is why most of them list 30 to 55 gallons (115 to 200 liters) as a minimum. Most are undemanding about water and do well in neutral to moderately hard conditions, roughly pH 6.5–8.0 and 72–86°F (22–30°C); the profiles flag the soft-water and cool-water exceptions. They eat flake, pellets and frozen foods without fuss. Give them clear swimming room down the middle with planted edges, a lid because they jump, and time: a drab juvenile becomes a coloured adult over the first year, and the big species live five years or more.

Blue-eyes and threadfins for nano tanks

The blue-eyes (Pseudomugil) and the threadfin rainbowfish stay between 1.5 and 3 inches (3.5 and 7 cm) and are happy from 10 to 25 gallons (40 to 95 liters). They are gentle fish for gentle company: keep them with small, calm tankmates, feed fine foods such as baby brine shrimp and crushed flake, and give them floating plants or spawning mops to display over. Their lives are shorter than the big rainbows, which is one reason they are often bred at home. The Popondetta blue-eye is the easy one to start with; the forktail, red neon and spotted blue-eyes and the threadfin follow once the tank is settled.

Cool-water rainbows

Not every rainbowfish wants a tropical tank. The Australian rainbowfish, the Lake Kutubu and Lake Tebera rainbowfish and the Pacific blue-eye all list temperatures from around 68°F (20°C), and the desert and Duboulayi's rainbowfish go lower still. The first four top out at 77–79°F (25–26°C) and will sulk in the 82°F (28°C) most community tanks run at; they suit an unheated room or a tank shared with other cool-water fish. The desert and Duboulayi's rainbowfish take the warm end as well. Check the temperature range on the profile before mixing them with warm-water species.

One species per tank if you want pure lines

Melanotaenia rainbowfish hybridise freely, and the offspring are fertile and hard to identify. Serious keepers run one species per tank or, at most, one species per genus. If you are not breeding them a mixed school is fine and looks good, but do not pass the fry on as a named species. The blue-eyes are a separate family and do not cross with the larger rainbows, and neither do the Madagascar and Celebes rainbowfish, which are here by name and habit; the Celebes rainbow is marked difficult and wants hard, alkaline water.

By the numbers

Smallest

Largest

Easiest to keep

Fits a 20 gallon tank

Fits a 30 gallon tank

FAQ

Common questions

How many rainbowfish should be kept together?

Six or more of one species, with several males. They school, and the males colour up when they have rivals to display to.

What size tank do rainbowfish need?

The 4 to 6 inch (10 to 15 cm) melanotaenias want a 4 foot tank, listed as 30 to 55 gallons (115 to 200 liters) depending on species. Blue-eyes and threadfins are happy from 10 to 25 gallons (40 to 95 liters).

Why are my rainbowfish not colourful?

Age and company. Juveniles are drab, colour arrives over the first year, and males show it when there are other males to compete with. Colour is strongest in the morning and during displays. Poor water and a lone fish both dull it.

Are rainbowfish aggressive?

No, but they are boisterous. A large school of big melanotaenias can outcompete slow or long-finned fish at feeding time. Keep them with other active mid-water fish.