Breeding Rasboras: How to Breed Rasbora Fish

Rasboras are common freshwater aquarium fish known for their simple care needs and peaceful nature. Because this fish is so common it’s often the subject breeding attempts by hobbyists. If you’re thinking about trying to breed this species you’ve come to the right place. In this guide we’ll cover the most common facts you’ll need to know when preparing to successfully spawn Rasboras.

The Rasbora genus includes a large variety of fish, from the large Scissortail Rasbora which can reach three inches to tiny Chili Rasboras that never grow longer than one inch. While Rasboras have a range of different sizes and appearances their breeding habits have many similarities which makes it simple to provide general guidelines to prospective fish breeders.

Harlequin Rasbora
Harlequin Rasbora

Are Rasboras easy to breed?

While Rasbora fry have straightforward care needs it can be a challenge to coax some Rasbora species to breed. In captivity this fish lacks common food sources and environmental changes which encourage spawning. While some of these can be duplicated in home aquariums, preparing some Rasboras to spawn can be difficult. This varies somewhat depending on species, and some Rasboras will spawn more readily. Less timid fish such as Chili Rasboras will spawn continuously when properly fed. On the other hand, Harlequin Rasboras have specific water requirements and pose a challenge to most home breeders.

Do Rasboras breed a lot?

Some Rasbora species will continuously spawn when properly fed. Chili Rasboras are in this group and are some of the easiest Rasboras to breed. Generally, Rasboras are more difficult to breed than some other freshwater fish such as Guppies. Commercial breeders will often induce spawning by using breeding hormones such as Ovaprim along with other proprietary additives. Home breeders usually prefer to encourage breeding naturally. This means trial and error along with some common rules of thumb.

How to breed Rasboras

Rasboras breed in groups which must be provided live food, with soft and acidic water. Java moss or breeding mats should be included in the breeding tank to catch and protect eggs after spawning. It’s a good idea to include an air powered sponge filter as this is safe for eggs and fry.

Rasbora Breeding Behavior

Rasboras are mainly an egg scattering species that doesn’t show parental care. Eggs will be deposited and fertilized over the course of around 4 to 5 days. Precautions must to taken to prevent adults from predating eggs and fry. Some Rasbora species such as Harlequins will spawn on the underside of leafs, commonly Java Fern or similar. The female will press her belly to the underside of leaves, coaxing a male to join her. Sometimes the resulting fertilized eggs will stick to the underside of the leafs, but can also fall toward the bottom of the tank. Most Rasbora species simply scatter eggs as they are expelled and fertilized.

Male vs Female Rasboras

Often, female Rasboras will be larger and rounder than the males which are smaller, slimmer, and can have more vibrant colors. The rounder body shape of females becomes obvious as they fill with eggs in preparation for spawning.

Optimal conditions for breeding

Rasboras need access to live food, with soft and acidic water to stimulate breeding behavior. In some cases it can be ideal to include plants with wide leafs which may help stimulate spawning, particularly in Harlequin Rasboras. Tank setup, temperature, and water chemistry must all be correct to successfully breed Rasboras. In the following sections we’ll take a closer look at these three parameters to discover how they should be adjusted for best breeding results.

Tank setup

Rasboras should be provided separate breeding tanks with leafy plants and ground cover such as Java moss. Adult Rasboras can predate eggs, and Java moss can protect some eggs until spawning is complete and adults are removed from the tank. Java moss isn’t a perfect solution and some breeders opt for placing a layer of breeding mesh along the bottom of the tank. Breeding mesh allows eggs to fall through to safety while blocking access from hungry adults. The breeding tank should be equipped with an air powered sponge filter which is safe for both eggs and fry.


Rasbora breeding tanks need stable water temperature and submersible heaters are the best choice. Water temperature should be between 75° and 80° for most species. Some breeders will slowly drop this temperature to simulate seasonal changes in an effort to trigger spawning.

Water pH

Rasboras need soft and acidic water to encourage breeding. Many breeders use RODI water and adjust water acidity down to a pH of 5.0. Some hobbyists report that dropping pH to 4.4 triggers spawning! This is a more extreme adjustment and should be undertaken slowly. Some species, such as Fire Rasbora, are sensitive to water chemistry changes and rapid pH swings may harm or kill them. If you plan to greatly lower pH it’s best to do it slowly over the course of a few days.

While not strictly related to pH, some breeders will introduce blackwater extract to their Rasbora breeding tanks. Blackwater extract helps to simulate natural Rasbora environments which often contain decaying plant matter.

Rasbora eggs

The appearance of Rasbora eggs varies between species, but all are small. In some of the smallest species the eggs can be difficult to spot with the naked eye. Understanding Rasbora eggs and their care needs is key for successfully breeding any Rasbora species. In the following sections we’ll cover what you’ll need to know when working with Rasbora eggs.

Do Rasbora lay eggs?

Rasbora aren’t livebearers and will scatter eggs externally. Females preparing for spawning will plump with eggs, but they aren’t “pregnant” in the same way as livebearing fish like Guppies or Mollies.

What do Rasbora eggs look like?

Rasbora eggs look like tiny milky white pearls. The smallest species may have tiny eggs that are difficult to spot with the naked eye. They can be easier to see when scattered in green Java moss or stuck to the underside of broad leaf plants as is the case with Harlequin Rasboras.

How long do Rasboras carry eggs?

Female Rasboras will plump with eggs over the course of a few weeks until spawning starts. Spawning takes place over 4 to 5 days after which time all eggs are expelled.

How do I know if my Rasbora is carrying eggs?

Female Rasboras will become noticeably plumper as their bodies fill with eggs. Watching your Rasbora breeding school over a long period will help you discover when females are beginning to plump with eggs in preparation for spawning.

How long does it take for Rasbora eggs to hatch?

Rasbora eggs hatch quickly, often within 24 to 48 hours. This quick hatching time means that extra precautions against fungus won’t usually be necessary. Proper filtration is important for protecting against fungus, and this may be all that is needed to protect Rasbora eggs in most cases. Some breeders will add a small amount of Malachite Green to breeding tank water to discourage fungal growth. Consider using a turkey baster or similar tool to move eggs to a nursery box hanging inside your breeding tank. Advantages of nursery boxes include keeping eggs off tank bottoms where they have greater exposure to fish waste. Elevating eggs can help keep them in water with higher oxygen content which is important for health of newly hatched fry.

Rasbora fry

Once Rasbora fry hatch they become free swimming after a few days. It’s a good practice to lower or turn off tank lighting until fry begin swimming on their own. Young fry can be sensitive to bright light and they won’t have the benefit of cover plants like they would have in nature. It takes a few weeks to a couple of months before Rasbora fry are large enough to start eating adult foods. They should be kept in the breeding aquarium were you should perform regular 10% water changes.

How to raise Rasbora fry

It’s best to keep eggs and the newly hatched fry in nursery boxes inside the main breeding aquarium. This keeps fry higher in the aquarium where water oxygenation is greater and away from the tank bottom where waste collects. Direct a gentle flow or drip of water into the nursery box to provide circulation. Using nursery boxes inside a larger breeding aquarium can make feeding easier as food can be concentrated where fry can eat it. Also, you have the benefit of a larger volume of water to keep water chemistry stable.

What to feed Rasbora fry

Rasbora fry initially only eat tiny foods such as Paramecium. Live Paramecium are often cultured for very small fish fry who aren’t able to eat anything larger. This will include your newly hatched Rasbora fry for the first few days. Try to move your fry to larger live foods such as newly hatched brine shrimp as soon as possible. Other foods to try include microworms including vinegar eels. Vinegar eels are more difficult to raise than other microworms but they can live and swim in water for longer. Keeping fry in a nursery box makes feeding easier as small foods can be concentrated where fry can easily find them. Rasbora fry will eventually begin eating adult foods, including feeding on chunks of prepared and frozen meaty foods.

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