Black Ruby Barb
Pethia nigrofasciata
Cyprinidae
About
A Sri Lankan endemic from the shaded hill streams running between the Kelani and Nilwala basins, the black ruby barb is a stocky, deep-bodied little cyprinid of about 6 cm. Juveniles in shop tanks are easy to walk past: a plain yellowish body crossed by three black vertical bars. Mature males are a different animal entirely, and in spawning condition the flanks darken almost to black while the head and forebody flush deep crimson-purple. It is a busy mid-water shoaler that patrols planted thickets all day, and the males spend much of that time displaying at one another, which is exactly what keeps their colour up.
Care
Keep a shoal of at least eight in 80 litres or more with a footprint of 80 cm plus; in groups under six they turn nervous and start nipping tankmates' fins. Soft, slightly acidic water at 22-26 C suits them, and because they come from cool shaded forest streams they stay comfortable down to 20 C, which makes them a poor match for species kept at 28 C. Use a dark sandy substrate, dense planting, leaf litter and floating cover, and keep chemistry steady with frequent small water changes rather than occasional big ones; very soft fine-leaved plants may get nibbled.
Diet
Feed a quality flake or micro-granule containing algae or vegetable matter as the staple, and add frozen or live daphnia, artemia and bloodworm several times a week for colour and condition.
Tankmate compatibility
Gets along with (89)
Possible with care (86)
Avoid (96)
Computed by the AquaSage engine for a spacious reference tank — always check the full verdict for your exact setup in the calculator.
Telling males from females
What works for this species, most reliable first.
- Colour and patternA hint only · from about 6 months, and only on a settled fish
In rainbowfish, killifish and several barbs the male carries the colour — deeper and more saturated, intensifying further when he displays.
- Extended finsA hint only · from about 8 months, and later in a suppressed male
On many cichlids and killifish the male's dorsal and anal fins draw out into trailing points as he matures, while the female's stay rounded.
- Belly depthA hint only · only on well-fed adults, and only as a comparison
For most tetras, barbs and rasboras this is all there is: a conditioned female is deeper through the belly than a male of the same length.
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Frequently asked questions
- What tank size does a Black Ruby Barb need?
- A Black Ruby Barb needs an aquarium of at least 80 litres (21.1 US gallons) with a footprint at least 80 cm (31.5 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Black Ruby Barb need?
- Black Ruby Barb does best at 20–27 °C (68–80.6 °F), pH 5.5–7.5 and a general hardness of 2–15 °dGH.
- What group size does a Black Ruby Barb need?
- Black Ruby Barb is a social species — keep a group of at least 8 so natural behaviour emerges and stress stays low.
- Is the Black Ruby Barb suitable for beginners?
- Yes — Black Ruby Barb is one of the easier species to keep and forgives typical first-tank mistakes, as long as the aquarium is cycled and maintained.