Blackline Rasbora

About

The Blackline Rasbora (Rasbora borapetensis) is a slender, silver-bodied cyprinid from the slow-moving ponds, canals, swamps, and shallow margins of rivers across Thailand, the Mekong and Chao Phraya basins, and the northern Malay Peninsula. It tends to live near the surface to mid-water in very shallow, sometimes murky conditions, which tells you a lot about how adaptable it is. The key field marks are a dark horizontal stripe running along the flank and a wash of reddish-orange at the base of the tail. The dorsal fin itself stays clear, which is how you tell it apart from the similar R. rubrodorsalis, whose dorsal sports a bright red blotch. In store tanks these fish can look a bit pale and unimpressive, but once they settle into a well-maintained aquarium they color up nicely and school with a tight, purposeful energy that makes them genuinely satisfying to watch. Keep at least eight to ten together. Smaller groups produce nervous, scattered fish, while a proper school brings out natural behavior and encourages males to show off their best colors. They coexist easily with other peaceful community fish of comparable size, and their undemanding water chemistry requirements mean they pair well with a wide range of tankmates. This is a species that rewards a bit of patience and proper group sizing.