Threadfin Rainbowfish
Iriatherina werneri
Melanotaeniidae
FishDifficulty: ●●●○○Data: well-established
About
The threadfin rainbowfish is a tiny, exquisitely finned species from the swamps and slow tributaries of southern New Guinea and northern Australia. Males carry a raised first dorsal, a broad second dorsal and anal fin, and long black filaments trailing from the fins, which they flick open in near-constant display; females are plain and shorter-finned. Despite its beauty it is a poor fit for a standard community tank: it is slow, delicate-mouthed, easily outcompeted at feeding time, and its trailing fins are an obvious target for any nipper.
Care
Keep 6+ (10 or more is better, with two females per male) in a densely planted, gently filtered tank of at least 60 cm with only tiny, peaceful tankmates. Feed micro-foods several times a day.
Diet
Micro-predator with a very small mouth; live and frozen Daphnia, Moina, cyclops and brine shrimp nauplii plus powdered dry foods.
Tankmate compatibility
Gets along with (41)
African Butterfly CichlidAgassiz's Dwarf CichlidBamboo ShrimpBetta (Siamese Fighting Fish)Black Phantom TetraBolivian RamBronze CorydorasCherry BarbClown PlecoCockatoo Dwarf CichlidCongo TetraDwarf Flag CichlidDwarf GouramiDwarf Neon RainbowfishEmber TetraEmperor TetraGerman Blue RamGlowlight TetraGolden PencilfishGolden TetraHead-and-Tail-Light TetraHoney GouramiKribensisKuhli LoachLambchop RasboraMacmasteri Dwarf CichlidMarble HatchetfishPeaceful BettaPurple Emperor TetraRed Whiptail CatfishRosy TetraRummynose TetraSparkling GouramiSterbai CorydorasStrawberry RasboraStriped KribensisThick-lipped GouramiUpside-down CatfishVampire ShrimpX-ray TetraZebra Pleco
Possible with care (155)
Acei CichlidAgassiz's CoryAltum AngelfishAmano ShrimpAssassin SnailAuratus CichlidBanjo CatfishBlack Neon TetraBlack Ruby BarbBlack Skirt TetraBlackline RasboraBladder SnailBleeding Heart TetraBlood Parrot CichlidBloodfin TetraBlue AcaraBlue Dolphin CichlidBlue Tiger ShrimpBlue Velvet ShrimpBoesemani RainbowfishBorleyi (Redfin Hap)Borneo SuckerBrichard's TeleogrammaBrichardi (Fairy Cichlid)Bristlenose PlecoBuenos Aires TetraBuffalohead CichlidBumblebee CichlidBumblebee GobyButterfly Hillstream LoachCardinal TetraCelebes RainbowfishCelestial Pearl DanioCheckerboard CichlidCheckered BarbCherry ShrimpChili RasboraChinese Algae EaterChocolate CichlidChocolate GouramiClown KillifishCobalt Blue ZebraCochu's Blue TetraColombian Ramshorn SnailCongo Dwarf CichlidConvict CichlidCrystal Red ShrimpDemasoni CichlidDenison BarbDiamond TetraDiscusDoctor FishDojo (Weather) LoachDwarf Chain LoachDwarf Orange CrayfishDwarf Pea PufferDwarf RasboraElephantnose FishEllioti CichlidElongate MbunaEmerald CoryEndler's LivebearerFestivum (Flag Cichlid)Firemouth CichlidFive-bar CichlidFlame TetraForktail RainbowfishFreshwater ClamGhost ShrimpGlass CatfishGlowlight DanioGold BarbGolden Dwarf CichlidGreen DiscusGreen Neon TetraGuppyHarlequin RasboraHeckel DiscusHongi CichlidJapanese Trapdoor SnailJohanni CichlidJulii CoryKenyi CichlidKeyhole CichlidKissing GouramiLeast KillifishLemon TetraLeopard DanioLittle CorydorasMaingano CichlidMalaysian Trumpet SnailMarlieri CichlidMedaka RicefishMoonlight GouramiMultifasciatus Shell DwellerMystery SnailNeon TetraNerite SnailOdessa BarbOtocinclusPanda CorydorasParadise FishParaguay EartheaterPeacock CichlidPearl DanioPearl GouramiPenguin TetraPeppered CorydorasPlatyPolka Dot LoachPort CichlidPowder Blue CichlidPygmy CorydorasRabbit SnailRainbow CichlidRainbow SharkRamshorn SnailRed EmpressRed RainbowfishRed Zebra CichlidRed-Tail SharkRedhead CichlidReticulated Hillstream LoachRosy BarbRubber Lip PlecoRusty CichlidSalt and Pepper CorySaulosi CichlidScarlet BadisScissortail RasboraSerpae TetraSeverumSiamese Algae EaterSilver Tip TetraSimilis Shell DwellerSkunk CorySpotted HoploStar SapphireSulawesi Cardinal ShrimpSunshine PeacockSveni EartheaterT-Bar CichlidTaiwan Reef CichlidThai Micro CrabThreadfin AcaraThree-spot GouramiTiger BarbTurquoise RainbowfishUaru (Triangle Cichlid)Umbrella Dwarf CichlidVenezuelan CoryWhite Cloud Mountain MinnowWrestling HalfbeakYoyo LoachZebra Danio
Avoid (75)
Adonis PlecoAfrican ButterflyfishAngelfishBala SharkBlack Moor GoldfishBrevis Shell DwellerCalvus CichlidClown LoachComet GoldfishCommon GoldfishCommon PlecoCompressiceps CichlidCuckoo CatfishCylindricus CichlidCyprichromisDemon EartheaterDogtooth CichlidDuboisi TropheusDwarf Petricola CatfishElectric Blue AhliElectric Yellow LabEndlicheri BichirEven-spotted SynodontisFantail GoldfishFeatherfin SqueakerFigure-8 PufferFrontosaGoby CichlidGolden JulieGolden Wonder KillifishGreen Spotted PufferfishGreen TerrorIridescent SharkJack DempseyJaguar CichlidJewel CichlidKoiLemon CichlidLivingstoniMalawi EyebiterMalawi HawkMasked JulieMollyOcellatus Shell DwellerOranda GoldfishOrnate BichirOscarPeacock BassPictus CatfishPike CichlidRanchu GoldfishRed DevilRed TerrorRegan's JulieReticulated Flying FoxRostratusRosy Red MinnowRoyal PlecoRyukin GoldfishSailfin MollySailfin PlecoSalvini CichlidSand-sifting XenotilapiaShubunkin GoldfishSilver ArowanaSilver MoonyStriped Raphael CatfishSwordtailTelescope GoldfishTexas CichlidThreadfin PetrochromisTropheusVenustus (Giraffe Cichlid)Wolf CichlidZebra Mbuna
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 patternStrong · 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.
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Frequently asked questions
- What tank size does a Threadfin Rainbowfish need?
- A Threadfin Rainbowfish needs an aquarium of at least 60 litres (15.9 US gallons) with a footprint at least 60 cm (23.6 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Threadfin Rainbowfish need?
- Threadfin Rainbowfish does best at 22–30 °C (71.6–86 °F), pH 5–8 and a general hardness of 1–12 °dGH.
- What group size does a Threadfin Rainbowfish need?
- Threadfin Rainbowfish is a social species — keep a group of at least 6 so natural behaviour emerges and stress stays low.
- Is the Threadfin Rainbowfish suitable for beginners?
- Threadfin Rainbowfish 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.
Sources
Water & tank
Temperature22–30°C
Optimal temp.25–28°C
pH5–8
Hardness (GH)1–12°d
Carbonate (KH)0–8°d
Adult size4 cm
Min. volume≥ 60 L
Min. tank length≥ 60 cm
Group size≥ 6
Swimming zoneMid
TemperamentPeaceful
Water typeFreshwater
FlowLow
Lifespan~4 yrs
Try in the calculator