Ricefish Medaka Care Guide: Hardy Japanese Nano Fish

Japan’s outdoor rice paddies have shaped one of the most adaptable nano fish in the hobby. Oryzias latipes — the Japanese medaka, or ricefish — survives temperature swings from 5°C to 35°C, tolerates a wide pH range, and breeds prolifically with minimal intervention. A thorough ricefish medaka care guide is almost a study in what these fish don’t need: no heater in Singapore’s climate, no CO2, no specialist foods. What they do need is understood just as clearly. Gensou Aquascaping at 5 Everton Park, Singapore covers the full picture below.

Species and Varieties

Wild-type medaka are a subtle, silvery-gold fish around 3.5 cm, but selective breeding in Japan over decades has produced an extraordinary range of ornamental varieties now widely available in Singapore. Hikari (gold), Darumamedaka (round-body), Miyuki (iridescent blue), and Yuki (white) are among the more common forms. Some advanced varieties — the marble and the shiro-hikari — reach $10–$30 per fish at specialist shops, compared to $1–$3 for standard gold medaka. All varieties share identical care requirements; the differences are purely aesthetic.

Tank Size and Setup

Medaka are true nano fish and do well in tanks from 15 litres upward. They are active surface swimmers — an aquarium with greater surface area is preferable to a tall, deep one. A 60 cm long tank suits a group of 15–20 fish comfortably. A lid is advisable; medaka jump, particularly when startled. Fine-leaved surface plants like Salvinia or floating frogbit serve double duty as cover and as spawning substrate — females drape their fertilised egg strings among plant roots throughout the morning spawning period.

Substrate colour affects colour expression significantly. Medaka on dark substrate display richer, more saturated colouration due to chromatophore adaptation. Light-coloured substrates cause the fish to pale as they attempt to match their background.

Water Parameters and Singapore Climate Considerations

The adaptability of medaka is genuine. They tolerate pH from 6.0 to 8.5 and hardness from near zero to very hard. Singapore’s PUB tap water — soft, pH around 7.0–7.4, chloramine-treated — suits them perfectly after dechlorination. No heater is required; ambient temperature in Singapore’s indoor environments (28–32°C) falls within their preferred tropical range. At these temperatures their metabolism runs fast, growth is quick, and breeding is nearly continuous.

Outdoor tanks on balconies work well in Singapore for medaka — they are one of the few ornamental fish genuinely suited to outdoor cultivation in a tropical climate. Natural sunlight stimulates colour development and breeding, and seasonal temperature variation is negligible.

Feeding

Medaka accept virtually everything offered: high-quality micro-pellets, crushed flake food, frozen baby brine shrimp, daphnia, and even spirulina powder. Their small mouths require particle sizes under approximately 0.5 mm for adults; purpose-made medaka food (widely available from Japanese imports at specialty shops and on Shopee) is formulated correctly and worth using as a staple. Feed small amounts two to three times daily; medaka overeat readily, which degrades water quality quickly in small tanks.

Breeding

Spawning is the default behaviour of well-fed medaka in warm water. Females carry egg clusters attached below the vent each morning, which they deposit among plant roots or spawning mops over the first few hours of light. Eggs are clearly visible — a cluster of 5–20 attached to fine threads. If left in the tank, adults eat some eggs, but densely planted tanks with floating cover produce a steady supply of surviving fry. For serious production, collect egg clusters daily and incubate them separately in shallow containers with a drop of methylene blue to prevent fungal loss.

Fry hatch in eight to twelve days at 28°C and immediately hunt fine live food. Powdered fry food or infusoria for the first week, followed by baby brine shrimp nauplii, produces the fastest growth. Juveniles reach adult size in four to six weeks.

Common Health Issues

Medaka are genuinely hardy, but two conditions appear regularly. Bent spine — sometimes called lordosis — is genetic in some ornamental varieties and cannot be treated; affected fish often live normally but should not be used for breeding. Bacterial infections, usually presenting as frayed fins or ulcers, occur when water quality lapses in densely stocked tanks. Maintain nitrates below 20 ppm through regular water changes and the species proves remarkably disease-resistant under Singapore’s conditions.

Long-Term Keeping

Medaka live two to three years under good conditions. They age visibly — older fish tend to be slightly less vibrant and slower to spawn. Maintaining a breeding programme with overlapping generations keeps the population young and productive. The community around medaka keeping is large and active in Japan, with a growing following in Singapore; collectors on local forums trade rare varieties regularly, and some Japanese varieties unavailable in shops can be sourced through this network.

Related Reading

• Ricefish Medaka Colour Varieties: Platinum, Orange and Lame Scale
• Medaka Rice Fish Care Guide: Hardy, Beautiful and Easy
• Ricefish Varieties Guide: Platinum, Lame, Sparkle and More
• How to Aquascape for a Medaka Ricefish Tank: Surface and Open
• How to Aquascape a Ricefish Medaka Display Tank: Surface and Shade