Home / Fishes / Carp, barbs, minnows, loaches / Danionidae / Blackline rasbora
No federal permit to keepBlackline rasbora
Rasbora borapetensis
Fishes › Carp, barbs, minnows, loaches (Cypriniformes) › Danionidae (Danios and rasboras)
The blackline rasbora (Rasbora borapetensis) is a fish of the family Cyprinidae found in Asia in the Mekong, Chao Phraya, and Mae Klong basins, and also the northern Malay Peninsula.
Care at a glance
Species-specific aquarium care
- Tank: At least 24 in long and 12 in front to back for one adult (adults commonly reach about 3.9 in / 10 cm).
- Water: Freshwater.
- Temperature: 72–79°F (range recorded for this species).
- pH: 6.5–7.
- Hardness: 0–12 dGH.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Diet: FishBase classes it as a carnivore.
Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.
Care guide
Species care notes
- Tank: a base of at least 24 × 15 in (roughly 18 US gallons); space needed is rated “modest tank”.
- Water: 72–79 °F, 2–12 dGH.
- Behaviour: temperament peaceful; a shoaling fish best kept in a group of six or more.
- Difficulty: Easy (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Choice of decor is not especially critical although the fish tend to show better colouration when maintained in a well-planted set-up with a dark substrate.”
- Diet: “Stomach analyses of wild specimens have revealed it to be a micropredator feeding on small insects, worms, crustaceans and other zooplankton.”
- Tankmates: “This species is very peaceful indeed making it an ideal resident of the well-furnished community tank.”
- Breeding: “Like many small cyprinids this species is an egg-scattering, continuous spawner that exhibits no parental care.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Danios and rasboras
Applies to most species in this group. Habitat: These Asian fishes occupy habitats ranging from zebra-danio pools and rice paddies to shaded harlequin streams, rocky Devario streams and planted galaxy-rasbora wetlands. [fg159-zebra, fg159-harlequin, fg159-giant, fg159-galaxy]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- Use at least 90 × 30 cm (36 × 12 in) for zebra danios.
- Harlequins require at least 60 × 30 cm (24 × 12 in), shaded planted cover and subdued light.
- Devario aequipinnatus needs at least 120 × 45 cm (48 × 18 in), oxygenated water, moderate flow and a tight lid.
- Galaxy rasboras need dense planting and broken sight lines in at least 45 × 30 cm (18 × 12 in), with gentle sponge filtration.
- Match chemistry: harlequins pH 5.0–7.5, 1–12 dGH; galaxy rasboras pH 6.5–7.5, 5–15 dGH.
Climate & lighting
| Water | 64.4–77°F |
Diet
- Quality flakes or granules sized to the fish.
- Live or frozen Daphnia and Artemia.
- Bloodworms for zebra danios, harlequins and Devario.
- Small sinking foods for galaxy rasboras, which rarely feed at the surface.
Social life
- Keep zebra danios and harlequins in groups of at least 8–10. Galaxy males spar: dense cover and larger groups distribute aggression. Active Devario can overwhelm timid feeders.
Health watch
- Pseudoloma microsporidiosis in zebra danios.
- Pleistophora infection and columnaris can produce similar white lesions in zebra danios.
- Nipped fins among rival galaxy males.
Understanding the animal
About this animal
About this animal
In the aquarium trade, it is known by a variety of other names, including red-tailed rasbora, bora bora rasbora, and brilliant rasbora.
Quoted from the Wikipedia article “Blackline rasbora” (CC BY-SA 4.0) 174
In the wild
In the wild
From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.1
| Where it lives | Lives in freshwater, in rivers and streams, lakes. Uses both the bottom and open water. |
| Water it lives in | Freshwater, 72–79 °F (22–26 °C), pH 6.5–7, hardness 12 dH. |
| Climate | Tropical climate. |
| Behavior to plan for | Breeding: open water/substratum egg scatterers. |
What this means for care
- Keep water within its wild range, 72–79 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 94°F (up to 97°F in the hottest sampled areas) |
| Cool-season lows | about 64°F (down to 59°F in the coldest sampled areas) |
| Average temperature | 77–82°F across sampled records |
| Relative humidity | 71–75% on average (driest month about 62%) |
| Rainfall | about 1434 mm a year, with strong wet and dry seasons |
Measured at 104 wild occurrence records sampled against WorldClim 2.1 climate data (1970–2000 averages). Air conditions in the range are ecological context, not enclosure settings: microhabitats such as burrows, leaf litter or basking rocks can be cooler, warmer or more humid.
From the sources
From the sources
Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.
| Overview | The blackline rasbora (Rasbora borapetensis) is a fish of the family Cyprinidae found in Asia in the Mekong, Chao Phraya, and Mae Klong basins, and also the northern Malay Peninsula. In the aquarium trade, it is known by a variety of other names, including red-tailed rasbora, bora bora rasbora, and brilliant rasbora. — Wikipedia (community-edited) |
| Where it lives | Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase |
| Appearance and size | The blackline rasbora is a streamlined, silver fish with a dark brown or black, mid-lateral stripe reaching from the gill opening to the front of the caudal fin base. Above this line is a gold stripe. The caudal fin is bright red, and unlike Rasbora einthovenii, there is no black pigment. — Wikipedia (community-edited) |
| Biology | Occurs in swamps, ponds, streams and drains, usually in slow flowing, often somewhat turbid water. Found from midwater level to surface in nearly all ponds, ditches, canals and reservoir margins of 2 m depth or less. Inhabits medium to large rivers, flooded fields and brooks of the middle Mekong. — FishBase |
Data and studies
The numbers
The numbers
Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.
Adult length
Maximum recorded length. Measured as total length. Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
pH
Water hardness
Minimum tank footprint
Seriously Fish recommends a tank base of at least 24 × 15 in (about 18 US gallons).
Sources for this sheet
- FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
- Seriously Fish species profiles Experienced keeper or breederLong-running aquarium reference written and peer-checked by experienced fishkeepers and ichthyologists; each profile covers habitat, tank size, water, diet, behaviour and breeding.
- Seriously Fish: Zebra danio (Danio / Brachydanio rerio) Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish: Trigonostigma heteromorpha Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish: Devario aequipinnatus Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish: Danio / Celestichthys margaritatus Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
- iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.
More danios and rasboras
Barred danio
Devario pathirana
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Bengal danio
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Betadevario ramachandrani
Betadevario ramachandrani
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Blue danio
Danio kerri
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Brevibora cheeya
Brevibora cheeya
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Brilliant rasbora
Rasbora einthovenii
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