A delicate and exquisitely shaped nano rainbowfish native to New Guinea and Northern Australia. They are famous for the males' long, filamentous fins and butterfly-like display behavior. Due to their incredibly small throats, they require micro-foods. They are shoaling fish that are easily intimidated by boisterous tank mates.
Threadfin Rainbowfish At a Glance
Threadfin Rainbowfish Tank Requirements
Will Threadfin Rainbowfish fit in your tank?
Care guides tell you what Threadfin Rainbowfish needs, the next question is whether your tank can safely provide it. Test Threadfin Rainbowfish against your tank size, maintenance needs, and the fish you already keep before you buy.
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Threadfin Rainbowfish Water Parameters
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Threadfin Rainbowfish Temperament & Compatibility
Threadfin Rainbowfish Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Male
Features spectacular long fin filaments and brighter coloration. Males will 'spar' (display) without harming each other. Their fins are fragile and nip-prone.
Differs in 2 traits from base species
Also known as: Display Male
Female
Smaller fins and honey/silver coloration. Essential to keep in the tank to encourage male displaying behavior. Generally smaller than males.
Differs in 2 traits from base species
Threadfin Rainbowfish Care Guide Summary
The Threadfin Rainbowfish, scientifically known as Iriatherina werneri, belongs to the Rainbowfish family group. Adults reach a maximum size of approximately 5 cm and have a compressed body shape with a moderate growth rate. Classified as peaceful, this species primarily occupies the surface and mid-level zones of the aquarium and produces a low level of biological waste.
To thrive, the Threadfin Rainbowfish requires a freshwater only aquarium with a minimum volume of 60 litres and a tank length of at least 60 cm. Water temperature should be maintained between 23°C and 29°C, with a pH range of 5.5–7.5 and a general hardness of 1–12 dGH. A low water flow is preferred.
The Threadfin Rainbowfish is a rewarding species to keep, provided its core environmental needs are met. This species is available in 2 varieties: Male and Female. Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Threadfin Rainbowfish Habitat Setup
When setting up an aquarium for the Threadfin Rainbowfish, a low water flow best suits their natural preferences. Because this species occupies the surface and mid-level zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline and open swimming space in the centre of the tank for free movement. Useful additions include dense planting to provide cover, break sightlines, and reduce stress and floating plants to diffuse overhead light and create shaded areas. Keepers should note that a tight-fitting lid is essential, as this species is a known jumper.
Threadfin Rainbowfish Compatibility Notes
Classified as peaceful, the Threadfin Rainbowfish is a schooling species that feels most secure in a sizeable group, where natural shoaling behaviour reduces stress and brings out their best colours. When choosing tankmates, shy or slow-feeding tankmates may be outcompeted at feeding time. Selecting tankmates that favour different water layers from the surface and mid-level zones can help reduce competition and territorial overlap.
Threadfin Rainbowfish Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Threadfin Rainbowfish.
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
40 Gallon Breeder
Show 19 more tank sizes
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Frequently Asked Questions About Threadfin Rainbowfish
How big does Threadfin Rainbowfish get?
Threadfin Rainbowfish (Iriatherina werneri) typically reaches a maximum adult size of approximately 5 cm. They have a compressed body shape and a moderate growth rate.
What tank size does Threadfin Rainbowfish need?
A minimum aquarium volume of 60 litres and a tank length of at least 60 cm are recommended for Threadfin Rainbowfish. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Threadfin Rainbowfish need?
Threadfin Rainbowfish thrives in freshwater only conditions with a temperature range of 23–29°C, a pH between 5.5 and 7.5, and a general hardness of 1–12 dGH. A low water flow is preferred.
Is Threadfin Rainbowfish peaceful or aggressive?
Threadfin Rainbowfish is classified as peaceful with an aggression score of 1 out of 10. They are generally well-suited to peaceful community tanks.
How many Threadfin Rainbowfish should be kept together?
Threadfin Rainbowfish is a schooling species and should be kept in groups of at least 6. Larger groups help distribute aggression and encourage natural schooling behaviour.
Does Threadfin Rainbowfish have any special tank requirements?
Yes. Threadfin Rainbowfish benefits from plants - densely covered and plants - floating in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Does Threadfin Rainbowfish need a lid on the tank?
Yes. Threadfin Rainbowfish is a known jumper, and a tight-fitting lid or cover is essential to prevent escape. Even a small gap can be enough for a determined fish to leap out.
Top Tank Mates for Threadfin Rainbowfish
These fish are strong compatibility matches for Threadfin Rainbowfish based on water preferences, temperament, adult size, and tank behavior.
Golden Bristlenose Pleco
Ancistrus sp. L144
Ideal Tank MatesMalaysian Trumpet Snail (MTS)
Melanoides tuberculata
Ideal Tank MatesAssassin Snail
Anentome helena
Ideal Tank MatesBristlenose Pleco
Ancistrus cf. cirrhosus
Ideal Tank MatesHorned Nerite Snail
Clithon corona
Ideal Tank MatesRamshorn Snail
Planorbidae fam.
Ideal Tank MatesPlants That Suit Threadfin Rainbowfish
These plants pair well with Threadfin Rainbowfish based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Amazon Frogbit
Limnobium laevigatum
Asian Watergrass
Hygroryza aristata
Asian Watermoss
Salvinia cucullata
Carolina Mosquito Fern
Azolla caroliniana
Common Duckweed
Lemna minor
Crystalwort
Riccia fluitans
Fish Similar to Threadfin Rainbowfish
New Guinea Rainbowfish
Melanotaenia affinis
An active, schooling species native to the streams of northern New Guinea. Known for their striking lateral stripe and vibrant fin coloration that flashes during morning displays. They are peaceful but highly energetic, requiring ample open swimming space and highly oxygenated water to thrive.
MacCulloch's Rainbowfish (Dwarf Rainbowfish)
Melanotaenia maccullochi
A smaller, peaceful species of rainbowfish native to Australia and Papua New Guinea. They feature striking silver/yellow bodies with horizontal red, brown, or orange stripes. Unlike larger Melanotaenia species, their smaller size makes them suitable for medium aquariums. They are highly active schooling fish that require open swimming space and display their best colors in the morning.
Exquisite Rainbowfish
Melanotaenia exquisita
A highly active, schooling species native to the fast-flowing, clear streams of Australia's Northern Territory. True to their name, they display stunning metallic bodies with bright red-tipped fins. They require pristine, well-oxygenated water, plenty of horizontal swimming space, and should always be kept in groups of 6 or more.
Lorentz's Rainbowfish
Chilatherina lorentzii
A rare and beautiful rainbowfish native to slow-flowing, shaded rainforest streams in New Guinea. They thrive in unusually warm, alkaline waters compared to some other rainbowfish. As active, schooling fish, they require plenty of swimming space alongside dense planting and floating plants to mimic their natural shadowed habitat.
Bulolo Rainbowfish
Chilatherina bulolo
A rare and highly active rainbowfish native to the fast-flowing mountain streams and white-water rapids of the Markham and Ramu river systems in Papua New Guinea. They possess a silvery body with a distinct black streak on the upper and lower edges of the caudal fin. Because of their specialized natural habitat, they require highly oxygenated, fast-flowing water and alkaline conditions to thrive in an aquarium.
Banded Rainbowfish
Melanotaenia trifasciata
A large, robust, and highly active schooling fish native to Northern Australia. Famous for its intense geographic color variations (such as the red 'Goyder River' morph). They are peaceful but incredibly fast and vigorous swimmers, requiring long aquariums with plenty of open swimming space.