Filament Barb
Dawkinsia filamentosa
Cyprinidae
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About
Filament barbs are sold at four or five centimetres in a tank of other four-centimetre fish, and that is where the trouble starts. Seriously Fish gives a maximum standard length of 100-120 mm - so roughly 12-15 cm of fish once the caudal fin is counted - while FishBase lists 18 cm TL with a common length of 11 cm, and the USGS Nonindigenous Aquatic Species sheet gives 18 cm after Menon (1999). We gate on 15 cm, which is the conservative reading, and it is still triple the shop fish. The room it needs follows from that: Seriously Fish says 'an aquarium with base measurements of at least 120 * 45 cm or equivalent should be the smallest considered for long-term care', and the site's own note puts that at 243 litres. This is a Western Ghats fish, endemic to but widespread across Kerala, Tamil Nadu and southern Karnataka, most common in lowland coastal floodplains and found in fresh and brackish water alike - rivers, estuaries, coastal marshes and reservoirs. The name points at the trailing dorsal-fin rays, and here the sources genuinely disagree in a way worth knowing before you buy. Wikipedia and Maidenhead Aquatics both credit the filaments to adult males. Seriously Fish, citing Devi et al. (2010), says something more careful: 'Both sexes may develop filamentous rays in the dorsal-fin, depending on population, but apparently these are not always present and shed or absorbed outside the spawning season.' So a fish without filaments in the shop tank is not necessarily a female, and a male bought in full filament may lose them after spawning. One more thing worth knowing: older literature, including the USGS sheet, gives the native range as India, Sri Lanka, Burma and possibly Thailand. That predates Pethiyagoda and Kottelat's 2005 review, which split the 'Puntius filamentosus' group into several species, and the modern range is the Western Ghats one.
Care
A 120 cm tank from 240 litres, eight to ten fish, and water kept genuinely clean: Seriously Fish notes that because it comes from relatively pristine habitats it is 'intolerant to accumulation of organic pollutants and requires more-or-less spotless water in order to thrive', with weekly changes of 30-50% as routine and a high proportion of dissolved oxygen. Cooler than most tropicals - 22-25 °C, and Seriously Fish's published band stops at 25 - with pH 6-6.8 and hardness 2-15 °dGH. Be aware that hard Lithuanian tap water at pH 7.5 sits above every published range we could find for this species; Maidenhead Aquatics is the most generous at pH 5.5-7.0. Moderate water movement rather than a torrent, over rounded rocks and sand with hardy attached plants such as Microsorum, Bolbitis or Anubias - and note that two separate reasons point at the same short plant list. Seriously Fish's is the biotope: most aquatic plants will not thrive in that layout. Maidenhead Aquatics' is the fish itself - 'because of their appetite for all things green and leafy, only the more robust plant species (Java fern, Anubias sp. etc) should be chosen. Most other plants will end up on their menu!' It is the second reason that makes this entry not plant-safe, so plan a planted tank around attached ferns and anubias rather than around stems. Seriously Fish calls it 'an ideal addition to a peaceful community of riverine species' alongside other shoaling cyprinids and river loaches; Maidenhead Aquatics is more cautious and specifies a community with no long-finned fish. Our own reading of the two, and it is a reading rather than a citation: a 15 cm barb that never stops moving will unsettle slow, veil-finned tankmates whether or not it ever bites one. Males squabble among themselves inside a full group, which is where that energy should go - a trio concentrates all of it onto one fish.
Diet
Foraging omnivore - worms, insects, crustaceans, plant material and detritus in the wild. Good dried flakes and granules as the base with regular bloodworm, Daphnia and Artemia, plus green food, because it grazes all but the toughest aquarium plants.
Tankmate compatibility
Gets along with (163)
Possible with care (218)
Avoid (37)
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.
Similar species
Same category and the closest water parameters — if this species isn't quite it, start here.
Sold in Lithuania
These Lithuanian shops listed this species in their public catalogue (checked August 8, 2026). Stock moves — ask before you travel.
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Frequently asked questions
- What tank size does a Filament Barb need?
- A Filament Barb needs an aquarium of at least 240 litres (63.4 US gallons) with a footprint at least 120 cm (47.2 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Filament Barb need?
- Filament Barb does best at 20–26 °C (68–78.8 °F), pH 5.5–7 and a general hardness of 2–15 °dGH.
- What group size does a Filament Barb need?
- Filament Barb is a social species — keep a group of at least 8 so natural behaviour emerges and stress stays low.
- Is the Filament Barb suitable for beginners?
- Filament Barb sits in the middle of the difficulty scale — manageable for a careful beginner who has done the reading, but it has specific needs worth researching first.