Opsarius pulchellus (Butterfly Danio)

Opsarius pulchellus

Last updated on July 24th, 2022 at 06:27 pm

Native to India and Nepal, Opsarius pulchellus is a freshwater fish with an unusual appearance and care requirements that make it stand out from other species commonly kept in the aquarium trade.

The Butterfly Danio (also called Opsarius pulchellus) gets its name from the attractive markings on its body and fins that resemble butterfly wings. Danios are lively, peaceful fish that are great additions to community tanks.

Slightly smaller than the popular zebra danio, Opsarius pulchellus, commonly known as the butterfly danio, has a unique color pattern that makes it an attractive fish in any tank setup.

Studies suggest that anywhere from 50-90% of captive fishes die within the first week or two of being purchased, though there are several steps you can take to ensure your fish survives and thrives.

To help ensure your new fish makes it through their first few years with you, we’ve put together this comprehensive care guide for the butterfly danio which will serve as both an introduction to the species and a reference guide to their unique needs in captivity.

Origin and description

Opsarius pulchellus

The butterfly danio is one of the dozens of fish species native to southeast Asia. It’s part of a genus that has grown quite popular in aquariums over the last several decades. There are six known and recognized color variations for Opsarius pulchellus: red, orange, blue, purple, black/white spotted, and golden striped.

All have a relatively small size – less than 5 inches at full maturity – and have a lifespan of roughly 6 years under ideal conditions. They need slightly acidic water with a temperature range of 68 – 72 degrees Fahrenheit. They aren’t overly fussy about water pH, but wild-caught specimens should be slowly acclimated to your tank prior to introduction in order to prevent shock from sudden environmental changes.

Captive-bred butterflies are much more adaptable and can generally be added directly into your tank without worrying about health issues associated with sudden change.

Species profile

Opsarius pulchellus

The opsarius pulchellus is a pretty fish native to Pakistan and India. There are currently eight recognized species in the genus Opsarius; however, only one of these has been successfully kept in captivity by hobbyists. As such, there isn’t much-written information on keeping other species of opsarias in aquariums.

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However, many hobbyists have kept and bred opsarius pulchellus with great success using basic community tank maintenance standards.

Scientific name

The scientific name of the butterfly danio is opsarius pulchellus


They live in heavily planted freshwater and brackish water. They thrive in an aquarium with plenty of plants and surface area for swimming. They enjoy having a cave or rock to hide under, as well as floating plants for additional cover. They will occasionally venture out of these hiding places, however.

Butterfly danio size

Opsarius pulchellus can grow up to 4.3 inches (11 cm) in length.

Butterfly danio tank size

The minimum recommended tank size is 35 gallons per fish, and 55 gallons for a pair.

Tank set up

Opsarius pulchellus

For starters, you want to get a tank with a tight-fitting lid. Butterfly danios are notorious for jumping out of their tanks! A 35-gallon tank is sufficient for the fish; if your butterfly danios are very active, it may be worth going bigger.

The substrate can either be gravel or sand, as long as there are no sharp pieces in it, you don’t want any cuts on your fish! It should also make up about two inches deep on average. Plants do well in butterfly danios’ tanks, and they can even help keep nitrates down, but remember that you need to remove excess plant matter so that more nutrients aren’t introduced into your water than necessary.

The water temperature needs to stay between 75 and 80 degrees Fahrenheit at all times, which means an air conditioner or heater will likely be needed depending on where you live. You should aim for neutral pH, but since butterflies can survive better in slightly alkaline waters, adding peat moss might be beneficial.

Lastly, butterfly danios prefer being kept in schools of five or more of their own kind. This way they feel less threatened by predators like humans looking through them!

Butterfly danio tank mates

The opsarius pulchellus is best kept with other bottom-dwelling fish, like barbs and rasboras. Avoid keeping them with other danionins. They may eat some of your more sensitive fish, so if you have a small tank or young guppies, keep your butterfly danio on its own.

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If you do wish to house it with another fish species, consider putting your opsarius pulchellus in a separate tank to assess compatibility before fully integrating him into his new home. Common tankmates are tetras, barbs, rasboras, loaches, and other danionins. But not all danionins will do well together.

Some other danionins from Lake Tanganyika would make good tankmates for an Opsarius pulchellus including Mikrogeophagus ramirezi, Cyprichromis sp. aka synspilum, Tanichthys albonubes, and Tropheops sp. aka pretrei.

Juveniles can also be kept with tetras like Hyphessobrycon sweglesi or Paracheirodon axelrodi. The key to making sure your butterfly danios get along is to make sure there is plenty of room in the tank and plenty of territories that can’t easily be dominated by another fish.

Opsarius pulchellus breeding

Opsarius pulchellus

If you want to breed danio, it’s important to make sure they have enough room. Breeding is easy and straightforward, just put 2 males and 4 females in a tank. Breeders use either dimmed lighting or no lighting during spawning.

Put fine-leaved plants in a spawning tank so that eggs can be easily found. Eggs hatch in 24 hours and grow quickly. Fry feed on newly hatched brine shrimp for about 3 days, then add regular flake food. Males will take care of eggs until fries are ready to eat them after about 5 days.

Females may become aggressive towards other fish if not separated into a small breeding tank with only 1 male present. The male will care for and guard them once she has spawned with him as he knows she is carrying his offspring. A separate section of your main aquarium should be set up for raising young because adult danios are very territorial.

After about 9 – 12 weeks, babies begin displaying bright blue eyes instead of black/silver. This is how you can tell when they’re adult-size danios.

Are Butterfly danio aggressive or peaceful?

Although it seems as if they have a very aggressive nature, Butterfly danios are extremely peaceful, non-aggressive fish that should be kept in a community aquarium with other small peaceful fish.

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Butterfly danio care

Opsarius pulchellus

The fish is generally very hardy and easy to care for, tolerating most water conditions. It will tolerate a wide range of pH levels from 6.0 – 8.0 and temperatures from 68 degrees F to 75 degrees F. When first brought home, they may be sensitive to changes in water chemistry, so slowly alter water parameters over a week or two periods until you reach your desired values.

These can be kept singly or in pairs, but three fish is about as many as would cohabitate comfortably. Like all tropical fish, it should not be kept with species that are considerably larger than it as it does not have any large predatory teeth to defend itself against predators.

What do Opsarius pulchellus eat?

These guys are omnivorous and eat a variety of food including flakes, freeze-dried tubifex worms, frozen and live brine shrimp, and live daphnia. For maximum coloration and health, feed with a high-quality flake food supplemented with frozen or live foods several times per week. The water should be soft to slightly hard and they need alkaline pH between 7.5 and 8.0; anything below or above will cause stress on your fish.

Water parameters

Opsarius pulchellus

As with most fish, freshwater butterfly danios require a tank with clean, cool water. A general hardness level of 5–8dGH and a pH between 6.5 and 7.5 is ideal for your pulchellus, but these numbers can fluctuate based on your geographical location and other factors. As such, you should test your water parameters regularly to ensure that they fall within these ranges.

Opsarius pulchellus lifespan

The typical lifespan of an Opsarius pulchellus is 4 years, however, with good care, some fish have been known to live for 6 or 7 years in captivity.

Parasites and diseases

Keeping your opsarius pulchellus healthy is an essential part of owning these fish. These little guys are quite hardy and can survive in a variety of aquarium conditions, as long as you provide them with proper water quality and temperature. These fish are sensitive to heavy levels of ammonia and nitrite, so it’s important to keep their environment clean. Due to their sensitivity to a variety of diseases, you should ensure that their aquarium is free from other fish that carry parasites or diseases.

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Some common pests and diseases are Velvet/ich, Oodinium/ick, Epistylis/mud disease, protozoan infections such as Hexamita/cryptoccosis, Amyloodinium/Heterorhabditis worms.

Marine velvet is a parasite that infects fish in marine aquariums but can also infect freshwater fish in new aquariums with low nitrate levels. It can often be treated with some of the antibiotics that cure bacterial infections.


The butterfly danio is known to live in clear, calm waters. Its bright colors allow it to blend into its environment, making it difficult for predators to spot them. They are a bottom-feeder species and consume zooplankton and small insects that fall into their home habitat. Other larger fish have been known to eat these fish as well, but if kept in a controlled environment, they will not be able to reach your pet fish.

Common predators of Opsarius pulchellus are larger fish, foxes, and bats. You can house danios with most other fish as long as you get a large tank to give each species its own space, while still being able to swim around together. You can also purchase specific danio-specific tanks at pet stores if needed.

Do Opsarius pulchellus make good pets?

Yes. Like most types of fish, Opsarius pulchellus make excellent pets if they are given a proper home and cared for properly. Their bright colors and low maintenance requirements make them appealing, but if you decide to own one, it is important to know that it may only live for a year or two in captivity.