However, males change to a reddish (sometimes purple) color during the spawning season (March to September) which functions to attract females.

The female rosy bitterling has a unique pipe about the same length as its own body, used for laying eggs on a specific spot of mussels.

A male spawns into the gill cavity of the mussels right after a female lays eggs to ensure fertilization.

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

[10] Because of these interbreeding events, the number of R. smithii has dramatically declined all over Japan and now is in danger of extinction.