Blackline rasbora Care Guide: Diet, Tank Mates, Diseases, Breeding & More

Updated: December 17, 2022

The Blackline Rasbora is a peaceful and hardy freshwater fish that is perfect for beginner aquarists.

This species is relatively easy to care for and can live in a wide range of water conditions. They are also very peaceful, making them a perfect addition to community tanks.

Blackline Rasboras are a relatively new species that was only discovered in 2006.

Species overview

Blackline rasboras (Trigonostigma hengeli) are a small freshwater fish that’s native to various parts of Southeast Asia.

They are heavily concentrated in Malaysia, Indonesia, and Thailand but have also been found in small numbers in Cambodia and Vietnam.

Blackline rasboras prefer slow-moving water with a lot of vegetation. This could be in the form of a river, stream, or even a swamp.

As far as their diet goes, blackline rasboras are omnivores. In the wild, they eat a variety of small insects, crustaceans, and plants.

Blackline rasboras are a very popular freshwater fish due to their small size and peaceful nature. They are compatible with a wide variety of tank mates and make a great addition to any community aquarium.


Blackline rasbora

As the name suggests, these fish have a very distinct black line that runs from the front of their mouths, all the way back to the base of their caudal peduncle.

This line is very dark and really stands out against their body which is a bright silver color. The line itself is actually made up of a series of black dots that are close together.

The fins on this fish are also black except for the very tips which are transparent. The dorsal fin is slightly taller than the anal fin and both of these fins are positioned towards the back of the fish.

The caudal fin is forked and symmetrical. Blackline Rasboras have a long and thin body shape that gives them a lot of speed and agility.


The lifespan of blackline rasboras in captivity is around 3 to 5 years. As with all fish, there are a number of factors that can impact their lifespan.

The quality of their environment is probably the biggest factor. If the water is too warm or too cold, has the wrong pH, or is too dirty, blackline rasboras won’t live very long.

They’re also pretty sensitive to stress. So, if they’re constantly being harassed by other fish or don’t have enough hiding places, their lifespan will be shorter.


Blackline rasboras only grow to be around 1.5 inches in length when fully matured. This makes them one of the smaller freshwater fish species that you can find.


Tank Size

The minimum tank size for blackline rasboras is 10 gallons. This is assuming you’re keeping them in a school of at least 5 or 6 fish (which you should).

We personally recommend a slightly larger tank if you can accommodate it. Every extra space will make a big difference and allow you to keep a larger school or more tank mates if you’re interested in a community tank.

Water Parameters

The blackline rasbora is a tropical fish that prefers warm water with a neutral to slightly acidic pH.

They’re found in slow-moving streams and rivers in Southeast Asia. The water is typically soft with low dissolved minerals.

Rasboras are a schooling fish, so you’ll need at least six of them. A larger group is even better. The more fish you have, the more comfortable they’ll be.

A 20-gallon aquarium is the minimum size for a small school of blackline rasboras. If you want to keep a larger group, you’ll need a bigger tank.

  • Water temperature: 72 to 78 degrees Fahrenheit
  • pH levels: 6.0 to 7.5
  • Water hardness: 2 to 8 dGH
  • Alkalinity Levels: 4-8 dKH

What To Put In Their Tank

As we mentioned before, these fish are wild caught and come from all sorts of different environments. This means that they’re adaptable to a wide range of different tank setups.

The substrate is one area where you have a bit of freedom. A lot of people prefer to use sand because it’s softer on the fish and looks nicer in general. Gravel is perfectly fine too though.

When it comes to plants, you can go with whatever you want. Hornwort, Water Wisteria, and Java Moss are all great choices that can handle a bit of abuse.

Rocks, driftwood, and caves are all great choices for decorations. Avoid anything too small though since these fish like to have some room to swim.

A classic gravel substrate is always a good choice, but you can do with something soft and sandy if needed too (use other species you keep as a guide with this).

Common Diseases

Thankfully, blackline rasboras are quite hardy fish. They don’t seem to be too susceptible to any particular disease or illness.

However, that doesn’t mean they can’t get sick. Just like any other fish, they can fall ill if the water quality in their tank is poor or if they’re not being fed a nutritious diet.

The most common illness that these fish experience is ich. This is a parasite that will attach itself to your fish and cause them to develop white spots on their body.

If left untreated, ich can be fatal. However, it’s fairly easy to treat if you catch it early. There are plenty of ich treatment options available, so consult your vet or do some research online to find the best one for your fish.

Another thing to keep in mind is that blackline rasboras are quite sensitive to changes in water quality. So, if you notice anything out of the ordinary it’s important to act fast.

The best way to prevent your blackline rasbora from getting sick is to maintain a clean and stable tank. These fish are relatively low-maintenance, but they still need pristine living conditions to stay healthy.

Behavior & Temperament

The Blackline rasbora is a shy fish that likes to stay hidden. In the wild, they live in dense vegetation where they can stay out of sight.

In the aquarium, they’ll do the same thing. They’ll find a place to hide and stay there until they feel safe enough to come out. Once they’re out, they’ll school with other Blackline rasboras.

These fish are very peaceful. They won’t bother other fish and they’ll only eat food that sinks to the bottom of the tank.

Tank Mates

The blackline rasbora is a peaceful and social fish. In the wild, they live in large schools and do best when kept in groups.

We recommend keeping at least 6 blackline rasboras together. This will help reduce their stress levels and make them feel more comfortable in their environment.

When it comes to choosing tank mates for blackline rasboras, look for species that occupy different areas of the water column.

These fish prefer to stay near the bottom, so top-dwellers are a good option.

Here are some compatible tank mates for blackline rasboras:


These fish can be a little difficult to breed in captivity. The biggest challenge is getting a group of these fish together in the first place. They’re not the most common fish on the market.

Assuming you can find a group of these fish, you’ll need to set up a breeding tank. It should be at least 30 gallons in size. The water should be soft with a slightly acidic pH. Keep the temperature between 75 and 80 degrees Fahrenheit.

Add some live plants and floating moss to the tank. These will give the fry somewhere to hide and plenty of places to feed.

When ready, add two females for every male. The males will be the ones with the more pronounced black lines on their bodies.

Feed the fish live foods and plenty of high-quality dry foods. Change about 50 percent of the water every week.

The female rasboras will lay their eggs in the live plants. The male will then fertilize them. Rasbora fry are very small, so you’ll need to use a fine-mesh net to remove them from the tank.

Place them in a separate fry tank with similar water conditions. Feed them live foods and plenty of high-quality dry foods.


The Blackline Rasbora is a great fish for the beginner aquarist. They’re easy to care for and will get along well with other community fish.

They’re also a very attractive fish, with their black and white stripes. They’re sure to add some visual interest to your tank!

If you’re looking for a low-maintenance fish that will add some beauty to your tank, the Blackline Rasbora is a great choice.