The Blackline Rasbora, often sold as the Red-tailed Rasbora, is a hardy and highly active schooling fish native to Southeast Asia. Recognizable by a bold black lateral line topped with gold and a bright red caudal fin, they are peaceful but energetic. They require plenty of horizontal swimming space in the middle to upper levels of the aquarium and must be kept in schools to feel secure.
Blackline Rasbora At a Glance
Blackline Rasbora Tank Requirements
Will Blackline Rasbora fit in your tank?
Care guides tell you what Blackline Rasbora needs, the next question is whether your tank can safely provide it. Test Blackline Rasbora against your tank size, maintenance needs, and the fish you already keep before you buy.
Useful setup supplies
We may earn from qualifying purchases
Blackline Rasbora Water Parameters
Water care products
We may earn from qualifying purchases
Blackline Rasbora Temperament & Compatibility
Blackline Rasbora Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Standard
The standard commercial form. As a prolific and fast-swimming schooling fish, they establish a dynamic hierarchy within their group. Because of their speed at feeding time, they can outcompete slower, shyer tank mates for food.
Same care requirements as the base species
Also known as: Wild Type
Blackline Rasbora Care Guide Summary
The Blackline Rasbora, scientifically known as Rasbora borapetensis, belongs to the Cyprinids family group. Adults reach a maximum size of approximately 6 cm and have a fusiform body shape with a moderate growth rate. Classified as peaceful, this species primarily occupies the mid-level and surface zones of the aquarium and produces a low level of biological waste.
To thrive, the Blackline Rasbora requires a freshwater only aquarium with a minimum volume of 60 litres and a tank length of at least 60 cm. Water temperature should be maintained between 22°C and 26°C, with a pH range of 6–7.5 and a general hardness of 2–15 dGH. A moderate water flow is preferred.
Due to its specialist needs, the Blackline Rasbora is best suited for fishkeepers who can provide a carefully planned setup. The Blackline Rasbora is typically available in one standard form.
Blackline Rasbora Habitat Setup
When setting up an aquarium for the Blackline Rasbora, a moderate water flow best suits their natural preferences. Because this species occupies the mid-level and surface zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline and open swimming space in the centre of the tank for free movement. Useful additions include driftwood, which can serve as both a hiding place and a dietary supplement, leaf litter or blackwater tannins to replicate their natural soft-water habitat, and dense planting to provide cover, break sightlines, and reduce stress. Keepers should note that a tight-fitting lid is essential, as this species is a known jumper.
Blackline Rasbora Compatibility Notes
Classified as peaceful, the Blackline Rasbora is a schooling species that feels most secure in a sizeable group, where natural shoaling behaviour reduces stress and brings out their best colours. When choosing tankmates, shy or slow-feeding tankmates may be outcompeted at feeding time and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the mid-level and surface zones can help reduce competition and territorial overlap.
Blackline Rasbora Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Blackline Rasbora.
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
40 Gallon Breeder
Show 19 more tank sizes
Feeding products
We may earn from qualifying purchases
.webp?2026-04-25T14%3A35%3A38.022Z)
Frequently Asked Questions About Blackline Rasbora
How big does Blackline Rasbora get?
Blackline Rasbora (Rasbora borapetensis) typically reaches a maximum adult size of approximately 6 cm. They have a fusiform body shape and a moderate growth rate.
What tank size does Blackline Rasbora need?
A minimum aquarium volume of 60 litres and a tank length of at least 60 cm are recommended for Blackline Rasbora. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Blackline Rasbora need?
Blackline Rasbora thrives in freshwater only conditions with a temperature range of 22–26°C, a pH between 6 and 7.5, and a general hardness of 2–15 dGH. A moderate water flow is preferred.
Is Blackline Rasbora peaceful or aggressive?
Blackline Rasbora is classified as peaceful with an aggression score of 1 out of 10. They are generally well-suited to peaceful community tanks.
How many Blackline Rasbora should be kept together?
Blackline Rasbora is a schooling species and should be kept in groups of at least 6. Larger groups help distribute aggression and encourage natural schooling behaviour.
Does Blackline Rasbora have any special tank requirements?
Yes. Blackline Rasbora benefits from plants - densely covered, driftwood (digestion/hiding), and leaf litter/blackwater in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Does Blackline Rasbora need a lid on the tank?
Yes. Blackline Rasbora is a known jumper, and a tight-fitting lid or cover is essential to prevent escape. Even a small gap can be enough for a determined fish to leap out.
Top Tank Mates for Blackline Rasbora
These fish are strong compatibility matches for Blackline Rasbora based on water preferences, temperament, adult size, and tank behavior.
Dainty Cory (Salt and Pepper Cory)
Corydoras habrosus
Ideal Tank MatesIncolicana Corydoras
Corydoras incolicana
Ideal Tank MatesEmerald Green Cory
Corydoras splendens
Ideal Tank MatesDuplicareus Corydoras
Corydoras duplicareus
Ideal Tank MatesLoxozonus Corydoras (C079/C082)
Corydoras loxozonus
Ideal Tank MatesAngelicus Botia
Botia kubotai
Ideal Tank MatesPlants That Suit Blackline Rasbora
These plants pair well with Blackline Rasbora based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Afzel's Anubias
Anubias afzelii
Amazon Sword
Echinodorus amazonicus
Anacharis
Egeria densa
Anubias Barteri
Anubias barteri
Baby Tears
Lindernia rotundifolia
Balansae
Cryptocoryne crispatula
Fish Similar to Blackline Rasbora
Brilliant Rasbora
Rasbora einthovenii
The Brilliant Rasbora is a peaceful, highly active schooling fish native to the forest streams and peat swamps of Southeast Asia. Known for its shimmering silver body and distinct dark lateral stripe, they thrive in gently flowing, heavily planted blackwater setups with subdued lighting. They are known jumpers, requiring a tight-fitting lid.
Harlequin Rasbora
Trigonostigma heteromorpha
A highly popular, peaceful schooling fish recognizable by its metallic copper/orange body and the distinct black triangular 'porkchop' patch on its hindquarters. Originating from peat swamps and blackwater streams in Southeast Asia, they are active swimmers that thrive in heavily planted aquariums with gentle to moderate water flow.
Chili Rasbora
Boraras brigittae
A striking, deeply red nano fish native to the blackwater streams and peat swamps of southern Borneo. They are extremely peaceful and require a mature, densely planted aquarium with soft, acidic water. Due to their tiny size, they are completely safe with adult dwarf shrimp and are ideal for nano setups.
Dwarf Rasbora
Boraras maculatus
A tiny, peaceful shoaling fish native to the blackwater streams and peat swamps of Southeast Asia. Known for their striking red/orange coloration and distinct dark body spots. They are an excellent choice for heavily planted nano tanks and peaceful dwarf shrimp setups. Because of their minute size, they are easily outcompeted for food and predated upon by larger fish.
Cherry Spot Rasbora
Rasbora rubrodorsalis
A peaceful and active nano cyprinid native to the slow-moving, heavily vegetated waters of the Mekong basin in Southeast Asia. It is characterized by a distinctive bright red spot on its dorsal fin and a dark lateral line. They are a somewhat shy but excellent shoaling species that thrives in blackwater or heavily planted setups.
Espei Rasbora (Lambchop Rasbora)
Trigonostigma espei
A small, peaceful schooling fish native to Southeast Asia. Closely related to the Harlequin Rasbora but distinguished by a more copper-orange coloration and a thinner, 'lambchop' shaped black marking on its flank. They thrive in heavily planted, mature aquariums with gentle water flow and slightly acidic water.