Japanese rice fish

Oryzias latipes is elongated and slender, typical of surface-dwelling fish. The back has a light brown to greenish-gray hue, while the sides fade to a silvery white belly. The fins, usually transparent, may have slight yellowish hues. The small mouth, oriented upwards, indicates adaptation for capturing prey at the surface.

This gregarious species frequents calm waters in small groups, preferring the surface and upper water column. Its activity is mainly diurnal. Omnivorous, it feeds on small invertebrates, zooplankton, insect larvae, and plant debris, picking them off the surface or among vegetation without active hunting behavior. Cohabitation with conspecifics is peaceful, with aggression being rare outside of the breeding context.

The reproduction of Oryzias latipes follows a precise cycle linked to the nycthemeral rhythm. Oocyte maturation occurs during the night, followed by ovulation at dawn. Fertilization is external but immediate: the male releases his milt near the female, and the gametes meet upon egg emission. A notable feature of this species is the female's post-spawning behavior: she retains the fertilized eggs, attached to her anal fin by fine filaments, for several hours, or even the entire day. This temporary carrying likely aids in better oxygenation and initial protection. The female then deposits her eggs by rubbing her abdomen against aquatic vegetation or other suitable substrate. No parental care is observed after egg attachment.