Family: Adrianichthyidae
A tiny, tolerant surface fish of rice paddies, easy to keep and breed in outdoor tubs.
The medaka is a two-centimeter survivor that has ridden rice agriculture for millennia. It is the classic outdoor-tub fish of East Asia — breeding in every season and asking only for clean water and sunlight.
Extremely — top-tier among coldwater minnows. 18–24 °C, slightly alkaline water and a 40 L tank produce a thriving group. They tolerate cold and low oxygen; the one weakness is sustained heat above 26 °C.
Yes, and they do better outdoors. Medaka come from rice paddies and ditches in Japan and Korea; a sunny outdoor tub through spring to autumn yields color and constitution far beyond indoor fish. Protect them from predators (cats, birds) and extreme rain-swings.
Medaka are egg-layers, gluing sticky eggs to plants; guppies are livebearers. Medaka tolerate cold and need no heater; guppies want 20 °C or more. Medaka are slimmer (4 cm) and gentler, mixing well with freshwater shrimp and small barbs.
Omnivores — micro-pellets, powder, brine shrimp and rotifers. Small mouths waste fast-sinking food. Since medaka are viewed from the side and above, fine floating food is best.
Very easily. Females deposit a few eggs daily on their pelvic-fin spawning brushes, then transfer them to plants or artificial mops. Collect eggs to a shallow dish — hatch in 1–2 weeks, first food is microworms or fine baby brine shrimp. Pick eggs daily for control, or fill the tank with moss for natural rearing.
They traditionally lived symbiotically in Japanese rice paddies — eating mosquito larvae and weed seeds through spring and summer, retreating to field-side ditches after harvest. This agricultural symbiosis remains living heritage in places like Niigata.
Above 26 °C they age faster, fade and lose appetite; past 30 °C losses occur. Southern summers need shade, a fan or frozen bottles. They're a cool-water fish — summer, not winter, is the real test.
Six minimum; schooling behavior shows at 10 or more. Groups form subtle hierarchies and display chases — small numbers stay timid. Ten to fifteen fish in 40–60 L is the sweet spot.
Any gentle cool-water fish: small barbs, bitterlings, topmouth gudgeons, similarly sized Chinese paradise fish. Avoid large or big-mouthed species — medaka are the textbook anything-can-eat-me size.
Dozens of cultivated strains: Yang Guifei (orange), white-light (platinum), Koujo (blue back), tricolor, transparent-scale and more. Common medaka cost cents; top show strains run to hundreds of yuan — the reason medaka culture endures in Japan.