Japanese Medaka

• It is one of the most widely used laboratory model fish, alongside the zebrafish, and was the first vertebrate to breed in space, in the mid-1990s.
• The female carries the eggs attached to her belly for a few hours before depositing them, which makes them easy to collect directly.

Skeleton type

Vertebrate - internal bony skeleton (bony fish)

Habitat and environment

Slow streams, irrigation ditches, paddy fields and coastal ponds of East Asia; it tolerates fresh to brackish water and moves between the two

Sexual maturity

At around 2 or 3 months old, at about 3 cm long

Gestation / incubation

10 days

Litter / clutch size

The female spawns once a day through the breeding season, with a peak of between 8 and 48 eggs a day at around 92 days old; total output per female ranges from 38 to 141 eggs

Life expectancy in captivity

Median lifespan of about 22 months under laboratory conditions

Sources consulted: Wikipedia (en): Japanese rice fish · Life-History Characteristics of Japanese Medaka (Murphy et al.) · eLife 46994, historia natural del medaka y sus parientes silvestres · NCBI PMC2952620, biomarcadores de envejecimiento en Oryzias latipes · NCBI PMC11706666, agotamiento espermatico en medaka · NCBI PMC11819472, observaciones de campo de cortejo y puesta en medaka (Gifu, Japon)

Best time: Breeding season from April to September in southern Japan, in marshes and paddy-field channels; both sexes mate almost daily through that period