(41) Threadfin rainbowfish

The threadfin rainbowfish (Iriatherina werneri), also known as the featherfin rainbowfish, is a small, stunning freshwater fish prized for the elaborate fin extensions of the males. Native to slow-moving, heavily vegetated waters in New Guinea and northern Australia, they are a peaceful and active species best suited for planted aquariums.

• Size: They are a nano species, with males reaching up to 1.6 inches (4 cm) and females being slightly smaller.
• Coloration: Their bodies are a subtle, translucent silver or gray, which shimmers with hues of yellow, green, and blue. A varied diet and a stable environment help bring out their best coloration.
• Fins: Males have distinctively large, feather-like extensions on their dorsal, anal, and pelvic fins. They use these fins in spectacular courtship and display dances. Females have much shorter, more understated fins. 

• Tank size: A 15- to 20-gallon tank is recommended for a school of at least 6 to 10 fish. The length of the tank is more important than the height, as they are active, open-water swimmers.
• Water parameters: Stability is key, as they are sensitive to fluctuations in water chemistry.
  • Temperature: 72–82°F (22–28°C).
  • pH: 6.0–7.0 is ideal, but they can tolerate a slightly wider range.
  • Hardness: They prefer soft to moderately hard water.
• Water flow: Unlike most rainbowfish, threadfin rainbowfish inhabit slow-moving or stagnant waters, so they require very gentle water flow. A sponge filter or a baffled filter outlet works best.
• Aquascaping: Replicate their natural, heavily planted habitat with a dark substrate, plenty of live plants (both rooted and floating), driftwood, and leaf litter. Floating plants help diffuse bright light, which these fish prefer. A secure lid is essential, as they are known jumpers. 

• Omnivorous: They are surface-dwelling omnivores.
• Varied diet: Provide a variety of high-quality foods, such as crushed flake food, powdered food, and small live or frozen foods like baby brine shrimp, cyclops, and daphnia.
• Outcompeted for food: They are slow eaters and can easily be outcompeted by other, faster-feeding fish. 

• Peaceful temperament: They are exceptionally peaceful and should only be kept with similarly tranquil, small species.
• Social fish: As a shoaling species, they should be kept in groups of at least 6 to 10 individuals. This will reduce their shyness, make them feel more secure, and encourage males to display their stunning finnage.
• Compatible tank mates:
  • Other peaceful nano fish, such as celestial pearl danios, pygmy corydoras, and otocinclus catfish.
  • Freshwater shrimp like Neocaridina (e.g., cherry shrimp) and Caridina species.
• Incompatible tank mates: Avoid fin-nippers, large or boisterous fish, and aggressive species. 

• Spawning: They are egg-scatterers and will lay adhesive eggs on fine-leaved plants or spawning mops.
• Fry care: The fry are extremely small and require infusoria or other microscopic foods for their first few weeks of life.