Rainbowfish – A Complete Care Guide

Rainbowfish, made famous by the children’s book of the same name, is actually a collection of more than 50 species that swim in every corner of the world. These splendidly colorful freshwater fish are popular home aquarium inhabitants. After exploring the varied characteristics and care needs of a number of the Rainbowfish species, you can decide which ones you’d like to add to your own tank.

Origin: Australia, Papua New Guinea, SE Asia

Rainbowfish Facts & Overview


Care Level:Easy
Temperament: Peaceful
Color Form:Various
Lifespan: 5 years
Size: 2.4-4.7 inches
Minimum Tank Size: 10-50 gallons, depending on species
Tank Set-Up:Freshwater with tall plants
Compatibility: Peaceful community

Rainbowfish get their name from their sparkling colors that change as light reflects off their bodies. These iridescent freshwater fish come from the family Melanotaeniidae, which has four subfamilies:

  • Melanotaeniidae (Threadfin, Sepik, Red, Parkinson’s, Millennium, Lake Kutubu, Dwarf Neon, Boseman’s, Banded, Australian)
  • Bedotiidae (Madagascar)
  • Pseudomugilidae (Blue Eyes)
  • Telmatherinidae (Celebes)

As you can see, the Melanotaeniidae subfamily has by far the largest species variety. All Rainbowfish originate from the lakes, rivers, streams, and swamps of Australia, Madagascar, and Papua New Guinea. Unfortunately, some Rainbowfish species are now endangered due to the introduction of invasive species into their biome as well as increased human activity.

Rainbowfish are bred in captivity in the United States (Florida) and Southeast Asia. In captivity and in the wild, Rainbowfish are shoaling fish that prefer swimming in groups of six or more.

Even though they are known for their gorgeous, light-catching colors, the Rainbowfish is not just another pretty face — these fish are also valued because they are robust creatures that can tolerate a varied water environment and they are adaptable to both peaceful and semi-aggressive tank habitats.

Generally, Rainbowfish range in size from 2.4 to 4.7 inches (6-12 cm), although the Van Heurn’s Rainbowfish can grow to 7.9 inches (20 cm). Note that Van Heurn’s is not usually found in home aquariums. If you’re thinking about this species, make sure you have a tank that’s large enough to accommodate this large and active swimmer.

See Related Article: Boesemani Rainbowfish – A Complete Care Guide

Typical Behavior

Rainbowfish are, for the most part, shy and unassuming. They are not known to be aggressive but they are social creatures who thrive in shoals of six or more.

They are happiest when they have an environment in which they can feel tranquil, so avoid putting your Rainbowfish in stressful situations, whether that stress comes from loneliness, tight quarters, or substandard water. Additionally, because they are rather docile and non-confrontational, they will hide when they feel threatened, which also causes stress.

In a behavior contrary to their naturally timid character, male Rainbowfish in large groups have the ability to brighten their color to attract the ladies. The males do tend to compete with each other, so you may see fighting and aggression during the mating season if your home aquarium has multiple males.

Make sure that you have a tight-fitting or weighted lid for your tank — Rainbowfish are capable jumpers when they feel threatened.

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Rainbowfish are marvelous and exotic creatures due to their glimmering color changes. You won’t tire of the spectacle of Rainbowfish in your home aquarium. The stunning colors of the many different Rainbowfish species are too varied to list here.

Rainbowfish share certain physical characteristics, as well. None of them have a lateral line, and they all have two dorsal fins that are located very close to each other.

Male Rainbowfish are distinguishable from females because they are more colorful; the same is true with age — the more mature Rainbowfish are more vibrantly colored. Female Rainbowfish are also slightly smaller than the males.

Read Related Reading: The Complete Guide to Boesman’s Rainbow Fish Care

Habitat and Tank Conditions

Rainbowfish are very active and enjoy swimming all day. Therefore, they appreciate a roomy environment where they can swim without impediment. To recreate their natural environment in lakes, rivers, streams, and swamps, they like fairly alkaline and hard water, with lots of plants they can snack on. Make sure to provide them with hiding places for when they feel threatened or scared.

Water specifications

Water requirements vary by species and subfamilies.

In their natural environment, Melanotaeniids swim in harder, more alkaline water; farm-bred species born in captivity can thrive in a variety of water conditions. Their best temperature range is 74°-78° F (23.3°-25.6° C) with a pH of 7.0 to 8.0 and alkalinity between 5° and 20° dKH (90 ppm to 360 ppm).

Bedotiidaes, like the Madagascar Rainbows, are accustomed to a more acidic environment. They prefer a temperature range of 74°-80°F (23.3°-26.7°C), a pH of 6.5 to 7.5, and alkalinity between 3° and 14° dKH (55 ppm to 250 ppm).

Pseudomugilids (Blue Eyes) prefer temperatures in the range of 76°-82° F (24.4°-27.8° C), with a pH of 6.5-7.5 and alkalinity between 5° and 10° dKH (90 ppm to 180 ppm).

Telmatherinidae (Celebes) like brackish water, so you can add a little aquarium salt (after you consider whether the Celebes’s tank mates can handle it). The temperature range should be 72.0-82.0° F (22.2 to 27.8° C), with a pH range of 7.0-8.0, and a hardness of 10 – 20 dGH.

If the room that houses your home aquarium is less than 74° F (23.3° C), make sure you have a heater for the tank. You’ll also need a filter that provides a moderate current to keep the water clean and the fish swimming happily. Performing a 25% water exchange every other week is recommended.

What Size Aquarium Do They Need?


Rainbowfish benefit from a long tank to accommodate their swimming habits — they love to have space to roam!

Smaller Rainbowfish like Threadfin and Blue Eyes can survive in 10-gallon tanks if you don’t have too many fish and in 20-gallon community tanks. Medium Rainbowfish like Boeseman’s or Duboulay’s need at least a 20-gallon tank. Red and Sepik Rainbowfish need a 40-gallon (151.4 liter) aquarium.

How Many Can Be Kept Per gallon?

You should plan to have ⅔ of a gallon (2.5 liters) of water for each small Rainbowfish, ¾ gallon (2.8 liters) for each medium-sized Rainbowfish, and 1 ½ gallon (5.7 liters) for large Rainbowfish. Here are some calculations:

  • 10 gallons (37.9 liters)=15 small Rainbowfish
  • 20 gallons (75.7 liters)=15 medium Rainbowfish
  • 40 gallons (151.4 liters)=15 large Rainbowfish

Tank Mates


Because Rainbowfish are such fast swimmers, they may make slower-swimming fish feel uncomfortable and anxious. It’s best to populate your Rainbowfish aquarium habitat with other fish that are of comparable size and temperament. Some compatible tank mates include:

Avoid the following tankmates:

Keeping Rainbowfish Together

Since Rainbowfish are shoaling fish, it’s preferable to keep them together. You should group at least 6 of the same species together. Additionally, different species of Rainbowfish should coexist peacefully.


Rainbowfish are omnivores and although they enjoy whatever you give them, it’s important that they have a combination of green vegetables and high-protein foods. In the wild, they consume mosquito larvae, so including live food in their diet promotes good health. Good foods to cycle in their diet include:

  • high-quality flakes with no fillers
  • pellets
  • betta treat
  • spirulina flakes
  • mysis
  • ground vegetables
  • frozen shrimp
  • blackworms
  • bloodworms
  • glassworms
  • mosquito larvae

Feeding habits

Try not to feed your fish the same thing every day. Rotate their menu items so that they have a variety of different nutritional sources. You’ll notice better color in your fish if you do. It also recreates the eating patterns in their natural environment.

Feed your Rainbowfish small amounts (whatever they can eat in two minutes) more frequently (up to 3 times a day). Because Rainbowfish are surface feeders, whatever they don’t eat will sink to the bottom of the tank.

That extra food results in poor water quality and puts your fish at risk for health problems.


Providing pristine water conditions, plenty of swimming space, and a varied and healthy diet, as well as mitigating stress will ensure that your Rainbowfish remain in top health — sounds a little bit like humans!

If you care for your fish in this way, they will be happy and healthy and therefore less likely to get sick.

You can tell if your Rainbowfish is healthy by its behavior and appearance.  A healthy Rainbowfish will have a good appetite, clear eyes, and their fins and tails will be intact.

Rainbowfish are easily stressed when they lack room to swim freely and when their water is dirty, both factors which you, as their guardian, can control.

Conversely, if your Rainbowfish loses color or its color dulls, your fish may be afflicted with a disease. Other warnings of illness include listlessness, uneven breathing, and spots of fungus on the fish’s body or mouth.

Common Diseases in Rainbowfish

Fin rot: Caused by substandard water quality, fin rot is seen in Rainbowfish quite often. Signs of fin rot, as you might imagine, are fins that look frayed or torn; their fins might also have redness at the base. Fin rot can be treated with antibiotics, but you will also have to treat the water to prevent it from returning.

Ich: Common in most aquarium fish and Rainbowfish are no exception. Ich is caused by a parasite called ciliated protozoan Ichthyophthirius multifiliis (hence the name Ich).  In addition to the telltale white spots on your Rainbowfish’s body and fins, you will notice strange behaviors, you might see them swimming erratically or rubbing up against hard objects.

Ich remedies are available over the counter, and you’ll need to quarantine any fish who are infected with Ich.

Speaking of quarantine: Anything you add to your tank, whether it’s a new fish, plant, or decorative cave, needs to be quarantined before you can add it to your tank. Inanimate tank additions should be thoroughly cleaned, as well.

Velvet: Also common in Rainbowfish, caused by a parasite called Oodinium. It’s noticeable by the dusty, brownish-gold color that your Rainbowfish will turn if afflicted by Velvet. You’ll notice similar behaviors to Ich infections.  Your Rainbowfish may swim erratically back and forth across the tank, or rub up against hard objects in an attempt to alleviate their discomfort.

If Velvet is left untreated, your Rainbowfish’s symptoms will worsen, and they will have difficulty breathing. They will likely stop eating, and, due to necrosis of the gill tissue, will eventually die.

This is why it’s so important to treat Velvet promptly. There are specific treatments for Velvet, but most of them contain copper, so if you also keep fish without scales (like Catfish or freshwater sharks), you’ll have to make sure to separate those fish during treatment.

Fun Fact: The Velvet parasite dinoflagellate uses photosynthesis to grow, so eliminating light from your aquarium while you are treating Velvet is a good idea.


Rainbowfish scatter their eggs and are, quite frankly, absentee parents who abandon their eggs as soon as they are laid.

It’s safe to say that Rainbowfish are more interested in spawning than in parenting, preferring to mate at the first sign of the day. Because of their enthusiasm, it’s not very difficult to breed Rainbowfish in your home aquarium. There are some things you can do to encourage the process, though.

  • Raise the water temperature in your aquarium
  • Offer a twice-daily varied diet.
  • Add a spawning mop to your aquarium and check for eggs daily

What on earth is a spawning mop? It’s a cork supported by a cotton thread that dangles into your tank; Rainbowfish will lay their eggs there.

When you find the opaque eggs, move the mop to an undecorated aquarium; this setting is where the Rainbowfish eggs will hatch.

Important note: Make sure the water conditions in the spawning tank are identical to the show tank; any variation in temperature, pH, or hardness could harm the eggs.

The Rainbowfish eggs hatch in the evening and are drawn to light. Hatching takes one to three weeks, depending on the water temperature and the species.

Fun fact: Rainbowfish, with their healthy procreative appetite, may mate with other species of fish. Spawning and hatching is a successful endeavor, but the fry is often stunted or discolored.

Once the new Rainbowfish larvae hatch, they will stay attached to the spawning tank until they have absorbed their yolk sacs. At this point, the larvae become fry that can swim freely and move toward the water’s surface.

Once the fry swim to the top of the water, you can feed them infusoria (essentially, algae), plankton, spirulina water, and liquid foods.

After about 14 days, they can tolerate fish food powder, and as they continue to grow, baby brine shrimp and microworms can be added to the mix.

Are Rainbowfish Suitable for Your Aquarium?

With the amazing array of coloration in these magnificent fish, it’s difficult to believe that they are one of the less popular types of freshwater fish. This may be due to the fact that the young Rainbowfish is not as colorful as more mature Rainbowfish, so they don’t stand out as much as some of the others.

But don’t doubt, these fish will really light up your home aquarium and you won’t be disappointed. Not only do they look great, but they’re fun to watch as they are active and swimming all day long. They are robust fish that are likely to thrive in a home tank as long as you provide them with a balanced diet, regular water changes, and plenty of room to show off their swimming prowess.

About Robert 386 Articles
Robert Woods is the creator of FishKeeping World, a third-generation fish keeper, and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America, and the Nature Conservancy.

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