Least rasbora

Geographic Origin and Biotope: Mekong basin (Thailand, Cambodia, Vietnam). Inhabits ponds, shallow swamps and flooded rice paddies covered by dense floating aquatic vegetation. It is not strictly a "blackwater" species.

Taxonomy and Morphology: Exclamation Point Rasbora (Boraras urophthalmoides). Regularly confused with B. brigittae. It has a tiny body with a sharp dark lateral line surmounted by a golden/copper line which, ending with a dot on the tail, resembles a horizontal "exclamation mark" (!).

Social Behavior: Extremely shy and highly gregarious. They hover or swim softly in unison. If the school is less than 15-20 individuals or the light is too strong, they will remain holed up on the bottom, even refusing food.

Coloration and Sexual Dimorphism: Transparent/bronze base coloration, with the bright golden and black line running along the flank. It lacks the bright red color typical of B. brigittae or merah. Males have a slimmer build and slightly more pointed fins.

Aquarium Setup: A 30L (8 gallons) nano-aquarium for a school. Clean water and excellent biological filtration but without current (they are terrible upstream swimmers). Lighting shielded by surface plants. Dark substrate recommended to highlight the golden color.

Diet and Feeding: Mid-water and bottom micro-predator. Needs very small live and frozen food: Cyclops, daphnia and microworms. Struggles to consume even the finest "nano" pellet, which must be further crushed between the fingers.

Water Quality: Compared to Indonesian Boraras it better tolerates neutral and moderately hard water, typical of the Indochinese floodplains. Requires aged and biologically stable water in any case.

Compatibility and Tankmates: The emblem of the harmless fish. Excellent companion for Caridinas (as the mouth is too small even for the zoeae). Ideal cohabitation with Trichopsis pumila (Pygmy Gourami) in well-planted tanks.

Aquarium Reproduction: Difficult due to the tiny size of the offspring. They scatter adhesive eggs among fine vegetation (Ceratophyllum). The tiny fry need green water (infusoria) for the first two weeks before they can eat nauplii.

Risks and Diseases: Very cheap species in stores and often purchased by beginners who put them with Angelfish or Cichlids that decimate them in a few hours. Fears strong temperature fluctuations and copper-based medicines.