[1] The fish reaches a length up to 6.5 centimetres (2.6 in), and is native to freshwater habitats with a pH of 6.8 to 7.8, a hardness of 20 DH, and a temperature of 10 to 25 °C (50 to 77 °F).

[4] It was widespread in the west side of Japan (Kyushu and western part of Honshū) before World War II.

In 1942, the rosy bitterling was accidentally introduced with grass (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) from mainland China.

[5] The two species are morphologically very similar, but several distinguishing characters are seen, such as the number of longitudinal scales, principal rays in the dorsal and anal fins, and shape of eggs.

[7] R. smithii was widely distributed in small ponds, reservoirs, and creeks in Kyushu and the western part of Japan.

Since R. smithii is critically endangered, nonprofit organizations and study groups were established in Japan to help protect this subspecies.

For example, this organization (Yao City, Osaka) made the protection pond in May 1999 where 41 male and 60 female fish were released with prawns.