Neon Blue Rasbora

About

Found in the peat swamps and slow, tea-dark forest streams of Borneo, Bangka, and Sumatra, Sundadanio axelrodi is a miniaturized cyprinid that barely clears three-quarters of an inch at full size. It was originally described as a rasbora and spent decades under that label before being reclassified into its own genus in 1999, where it remains the sole member. Its closest relatives are the equally tiny Paedocypris species, and like them it shares a preference for still or sluggishly moving, nutrient-poor waters with soft, acidic conditions. In the aquarium, soft blackwater chemistry with stable parameters is non-negotiable. This fish does not tolerate fluctuating conditions well, and that sensitivity alone puts it in the intermediate category rather than being a straightforward beginner pick. Where it really shines is in a dedicated, heavily planted setup with a decent-sized group of its own kind, ideally 20 or more individuals. With sufficient numbers, males become noticeably bolder, showing off their best coloration as they compete for female attention, and the collective movement of a proper school is genuinely rewarding to watch. Compatible tankmates should be small and undemonstrative. Similarly sized Boraras or petite South American characins work well. One handling note worth taking seriously: this species reacts badly to air exposure, so extra care during transport and acclimation is important.