Blackline Rasbora (Rasbora borapetensis): Care Guide

Also known as the Red-tailed Rasbora, the Blackline Rasbora has a striking silver body with a gold and black stripe running down its side to the caudal fin base which has a flare of red. This species originates in Asia’s Mekong, Chao Phraya, Mae Klong basins, and northern Malay Peninsula. This is a popular aquarium fish that does best in well planted aquariums with little water movement. A schooling fish, they prefer to keep in tight groups which can add movement and beauty to a freshwater tank. While they are micropredators in nature they don’t pose a threat to any fish which can’t easily fit in their mouths. They do require clean water and need excellent filtration along with regular feedings of high-protein, meaty foods. If you are planning on keeping or breeding this species there is some information you’ll need before adding them to your aquarium. We’ve put together this guide with all you’ll need to know when keeping this active and beautiful Rasbora species!

Blackline Rasbora (Rasbora borapetensis)
Blackline Rasbora (Rasbora borapetensis)

Blackline Rasbora Care

Blackline Rasboras need well planted aquariums and regular servings of high-protein foods. This fish is a schooling species that does best in groups of six or more. Planted aquariums are necessary for Blackline Rasboras to feel relaxed and comfortable, but plant maintenance adds extra complication to this fish’s care. Many planted tanks use CO2 injection which must be carefully controlled to aid plant growth without displacing too much oxygen or lowering water pH beyond what this species will tolerate.

Are Blackline Rasbora easy to care for?

Blackline Rasboras are hardy but need regular feedings of meaty foods and well maintained water. Because of the extra maintenance needed for best health, Blackline Rasboras can be slightly more difficult to keep than some other Rasbora species. With the proper preparation this fish can be a good choice for serious beginner hobbyists.


Blackline Rasboras prefer temperatures between 72° and 79° F. Temperatures in the upper part of this range can increase activity.

Water pH

Blackline Rasboras need water which is neutral to slightly acidic with a pH between 6.5 and 7.0.

Blackline Rasbora Size

Blackline Rasboras can reach a maximum size of around 2 ½ inches.

Food & Diet

In nature the Blackline Rasbora is a micropredator that feeds on small insects, worms, and other zooplankton. In the aquarium they can be fed a range of prepared flake and granular foods. The species should be provided regular feedings of frozen meaty foods such as brine shrimp and Daphnia. Adding meaty foods to this fish’s diet is important for best health and coloration.


Most Blackline Rasboras live five to seven years with quality care.

Tank Size

A school of six Blackline Rasboras can live in a ten gallon aquarium. If you are planning a larger school you’ll also need a larger aquarium. This species needs lots of horizontal space as they are very active swimmers. Short and wide tanks are a better choice than tall and narrow.

Tank Setup

Blackline Rasboras prefer well planted aquariums with lots of hiding space. Substrate choice will usually depend on how many plants you need to support. Most tanks will include two to three inches of nutrient rich aquarium growing soil such as ADA Aqua Soil. Substrates which support plants will also increase water acidity. Increased acidity is fine as this species is comfortable with slightly acidic water. It’s important to avoid any substrates or tank decorations which include coral. Coral can dissolve over time adding hardness and alkalinity that can harm this fish.

You’ll want a filter system which doesn’t create strong currents. Canister filters can cause too much water flow, creating an uncomfortable environment for the Blackline Rasbora. Even conventional filters can benefit from spreaders which break up returning water and prevent the creation of strong tank currents. Any filter you choose should be capable of turning over at least 5 times the volume of your tank in an hour. For instance, a 10 gallon aquarium will need a filter system capable or running at 50 GPH (gallons per hour) or more.

Many planted aquariums use CO2 injection for enhanced plant growth and reduce growth of nuisance algae. Added CO2 can displace oxygen and increase water acidity. Water chemistry must be watched closely to prevent harm to Blackline Rasboras. If you see your fish staying near the water surface trying to catch a breath this is a sign you’ve added too much CO2. CO2 concentration can be monitored by cost-effective drop checkers or more expensive and accurate electronic devices.

Blackline Rasbora in Aquarium
Blackline Rasbora in Aquarium


Blackline Rasboras are egg-scattering continuously spawners. Adults have no parental instincts and don’t care for eggs or fry. In a planted and mature aquarium a small number of fry may appear without any assistance from the hobbyist. Intentionally breeding this species will result in larger number of viable fry.

How do Blackline Rasbora breed?

Because Blackline Rasboras continuously spawn it’s difficult to plan for a specific egg-laying time. In most cases you’ll need to keep schools in prepared tanks and wait for eggs to appear. Expect females to lay 5 to 12 eggs at a time with a typical batch numbering 30 to 50 eggs. Laying breeding mesh along the bottom of the tank will allow eggs to fall through while protecting them from hungry adults. As soon as eggs appear, adults should be removed and relocated to another tank. Eggs hatch in 18 to 24 hours and fry become free-swimming in another 24 to 48 hours. Newly hatched fry are tiny and should be fed with Paramecia until they are large enough to consume microworms. Eventually they will be able to eat fresh and frozen brine shrimp. Feeding young Blackline Rasboras will result in uneaten food which will eventually spoil. Frequent and large water changes are necessary to keep aquarium water from fouling and killing young fry.

Blackline Rasbora eggs

Blackline Rasbora eggs are pearly white and only a few millimeters in diameter. They are a tasty treat for the adults and must be protected if you are wanting to breed this species.

Blackline Rasbora Male or Female

Blackline Rasbora females usually appear more full-bodied when viewed from above. This is especially true when they are getting ready to spawn and the female fills will eggs.


Blackline Rasboras are suceptible to a range of freshwater diseases such as fin and tail rot, cotton mouth, Dropsy, and Pop-eye disease. Many of these can be treated with appropriate medications, but prevention is easier than trying to cure sick fish. Impure water and overcrowded aquariums can place your fish at greater risk of contracting disease. Make sure your tank’s filter system is operating correctly and you are performing regular water changes. Keeping Blackline Rasboras in well planted aquariums can lead to lower stress levels and greater resistance to common diseases. It’s important to quarantine any new tank additions in a separate aquarium for 6 to 8 weeks to check for signs of disease before adding to your main tank.

Tank Mates

Blackline Rasboras are mostly peaceful when kept in schools of six or more. This species can happily coexist with a variety of common aquarium fish.

Examples of Compatible and Incompatible Tank Mates

Blackline Rasboras can be paired with other Rasboras, Betta, Danios, Loaches, or Corys. Avoid larger predatory fish such as large Cichlids or even Angelfish. Some normally predatory tank mates can be attempted in aquariums with enough plants for the Blackline Rasboras to hide when necessary.

Where can I find Blackline Rasbora for sale?

Blackline Rasbora are a popular aquarium species which can easily be bought at local fish stores or from online sellers. Because this is a schooling species you’ll want to buy at least 6 individuals.

Blackline Rasbora Price

Blackline Rasboras can be purchased for around $5 USD per individual. Sometimes discounts are available when buying more than one fish.

Blackline Rasbora vs Chili Rasbora

Chili Rasbora is much smaller than Blackline Rasbora, reaching a maximum size of less than one inch.  Both species are schooling fish which do best in groups of six or more individuals. Chili Rasbora is an omnivore which also appreciates the occasional feeding of meaty, high-protein foods similar to the Blackline Rasbora. Both species can coexist in the same tank and will form species-specific schools.

Blackline Rasbora vs Harlequin Rasbora

One of the most popular Rasbora species, the Harlequin Rasbora is even easier to obtain than the Blackline Rasbora. Harlequins are also known as Red Rasbora and have a reddish-copper body color with a black wedge covering the back half of their bodies. Harlequins are omnivores which benefit from occasional feeding with high-protein foods, as do Blackline Rasboras. The two species are similar sizes but Harlequins are slightly smaller and have a maximum adult length of 1 ¾ inches.

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