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Care guide · Freshwater · fish

Black ruby barb

Pethia nigrofasciata

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The black ruby barb (Pethia nigrofasciata) is a peaceful but active shoaling fish from Sri Lanka’s forest streams. Mature males develop a reddish-purple head and forebody, especially in breeding condition; three dark flank bars aid identification. Seriously Fish gives a maximum of about 5.5 cm standard length and recommends an 80 × 30 cm base, around 72 litres, with a group of six to ten. Prefer verifiably captive-bred stock and never release aquarium animals into natural waters. Provide a mature aquarium with sheltered margins and open swimming water. After introduction, check that the whole shoal remains active and feeds well.

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At a glance

Temperature
20–27 °C
pH
5.5–7.5
GH
2–15 °dGH
Aquarium length
At least 80 cm
Minimum aquarium volume
At least 72 L
Adult size
Up to 5.5 cm
Group size
At least 6–10 individuals
Temperament
Peaceful

About this species

The accepted name is Pethia nigrofasciata (Günther, 1868); Barbus nigrofasciatus and Puntius nigrofasciatus are former combinations. It is endemic to southwestern Sri Lanka. Three dark flank bars are characteristic. Males are slimmer and more colourful; breeding males develop a reddish-purple head and front body with darker fins. Females are usually larger and less vivid. FishBase reports a greater female total length than the standard length reported by Seriously Fish; these measurements are not interchangeable.

Natural habitat

The species inhabits the wet forest zone of southwestern Sri Lanka, including the Kelani and Nilwala basins. Typical sites are shallow, clear or slightly stained, shaded forest streams. Conductivity and hardness are generally low and water slightly acidic. Sandy bottoms are often covered with leaf litter and branches; marginal plants may overhang the stream.

Aquarium and layout

Seriously Fish recommends a base of at least 80 × 30 cm and about 72 litres. Give the shoal swimming room, with sheltered margins formed by plants, wood and optional floating cover. A dark substrate and subdued light may enhance colour. Good filtration and some movement are useful, while retaining calmer areas. Use a tight lid and mature the biological filter before stocking.

Water conditions

The specialist aquarium source recommends 20–27 °C, pH 5.5–7.5 and GH 2–15 dGH. FishBase lists older ecological values of 22–26 °C and pH 6.0–6.5; natural forest streams are generally soft and slightly acidic. This guide uses the broader aquarium range from Seriously Fish rather than blending values from different sources. Keep conditions stable and acclimate gradually.

Behaviour and group size

The black ruby barb is generally peaceful and social. Keep six to ten together. Choose tankmates for adult size, activity, swimming room and temperature needs; matching pH alone does not establish compatibility. Very small, slow or long-finned fish may be bothered by active barbs. Allow males to display without overcrowding the aquarium.

Feeding

In nature it forages on diatoms, algae, detritus, small insects, worms, crustaceans and other zooplankton. Use complete flakes or fine granules with plant or algal content as a staple. Supplement with small portions of suitable live or frozen foods such as Daphnia and Artemia. Distribute food so all fish can feed and remove leftovers.

Breeding

This is an egg-scattering species without parental care; adults may eat the eggs. FishBase reports spawning among marginal weeds, more than one hundred eggs and hatching in one to two days. A separate mature setup with fine-leaved plants or egg protection is better for deliberate breeding than a community tank. Remove adults after spawning and initially feed fry very fine food.

Sources & review

This care guide draws on several specialist sources and was last checked on .

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