Three-lined rasbora

The scissortail rasbora reaches about 15 cm standard length and is named for the twitching, scissoring motion of its tail fin when the fish holds station. It is native to the Chao Phraya and lower Mekong basins in Thailand, Laos and Cambodia, is widespread in Peninsular Malaysia, and reaches into Sumatra and Borneo. It is also called the three-lined rasbora, and it can be told from the similar Rasbora caudimaculata by the absence of red in the fins and from Rasbora spilocerca by its much greater size.

The habitats it has been collected from say a lot about how adaptable it is. Some are swift forest hill streams running over boulders, stones and sand, clear and close to neutral at pH 6.5 to 7.5. Others are sluggish blackwaters in ancient peat swamp forest, stained brown by decaying leaves, negligibly hard and acidic at pH 4.0 to 6.0. It also lives in reservoirs and lakes and moves into flooded ground during the wet season.

That range is why aquarium chemistry is undemanding: anywhere from pH 5.0 to 8.0 works depending on the origin of the fish, with 6.5 to 7.5 usually ideal, at 2 to 12 dGH and 22 to 25 °C. What the species does demand is space and clean water. A group needs a base of at least 120 by 45 cm, about 243 litres, with open swimming room, and it wants a mature tank rather than a freshly set up one. The lid matters as much as the filter, because this is a surface-dwelling fish and an accomplished jumper that will escape through the smallest gap. Temperament is genuinely peaceful, which makes it an easy fit alongside other cyprinids, tetras, livebearers, rainbowfish, anabantoids, catfish and loaches of comparable size.