Red Emperor Ricefish -RLF Line (Oryzias latipes)

Common Name

Red Emperor Ricefish, Red Emperor Medaka, RLF line

Scientific Name: Oryzias latipes

Origin and Habitat

Oryzias latipes is native to East Asia, especially across the Japanese archipelago, where it lives in rice paddies, irrigation ditches, ponds, and very slow streams with abundant vegetation and gentle flow. Habitats are shallow, sunlit, and seasonally variable, with calm water over sand, mud, and leaf litter. Red Emperor is a domesticated medaka strain refined by Japanese breeders. Medaka have been bred in captivity for many decades, which is why Red Emperor adapts well to most aquarium and outdoor tub conditions when water is clean, well oxygenated, and stable.

Temperature and Water Conditions

Aim for about 20 to 26 degrees Celsius, which is 68 to 79 Fahrenheit, for active behavior and reliable breeding. In the wild, medaka are reported from near neutral to slightly alkaline water, about pH 7.0 to 8.0, with hardness that varies by region. In aquariums, prioritize stability, good surface agitation, and regular partial water changes rather than chasing exact numbers.

Appearance and Size

Red Emperor is a vivid red to deep orange medaka line selected for strong body and fin coverage that reads beautifully from above and from the side. Adults are petite, generally 3 to 4 centimeters total length, which is about 1.2 to 1.6 inches. RLF stands for Real Long Fin. This trait produces elongated, flowing fins with clean tapering edges. Males typically show the longest extensions, with taller dorsal rays, a longer sweeping anal fin, slightly extended caudal lobes, and noticeably longer pectoral fins that paddle gracefully when the fish hovers. Females also carry the long fin trait but usually to a lesser degree. Juveniles lengthen their fins as they mature, and good nutrition plus calm, clean water help the fins develop straight and even.

Diet in the Wild

Wild medaka are omnivores that graze on small animal plankton and micro invertebrates such as daphnia and mosquito larvae, along with micro algae and plant material.

Feeding in Captivity

Provide a varied micro diet that mirrors the wild menu. Use small quality pellets or crumbs for ricefish, plus live or frozen baby brine shrimp, daphnia, and occasional mosquito larvae. Outdoor tubs with green water and natural micro life help bring out rich coloration. Offer light feedings two or three times daily so food is consumed quickly and water quality stays high.

Behavior and Tank Setup

Red Emperor ricefish are peaceful and lively near the surface and mid water. Keep them in groups of six or more so they display natural social behavior and steady activity. Give them floating and emergent plants for cover, gentle filtration, and a secure lid since medaka can jump when startled. A ten gallon aquarium or larger suits a small group. Use low to moderate flow, bright to dappled light, and open swimming space with fine plants for contrast.

Breeding

Medaka are daily spawners under warm temperatures and longer day length. Females carry a cluster of adhesive eggs briefly at the ventral area before attaching them to fine plants or spawning mops. At warm temperatures incubation is short. Fry begin with infusoria or green water, then progress to freshly hatched brine shrimp and powdered foods. For high yield, collect eggs from mops into a separate hatching container with gentle aeration and clean water.

Quick Facts

- Scientific Name: Oryzias latipes

- Strain: Red Emperor, RLF line

- Origin: Domesticated strain of a species native to Japan and East Asia

- Adult Size: 3 to 4 centimeters, about 1.2 to 1.6 inches

- Temperature: 20 to 26 degrees Celsius, about 68 to 79 Fahrenheit

- Wild pH: Commonly near neutral to slightly alkaline, about 7.0 to 8.0

- Temperament: Peaceful, best in groups

- Diet: Omnivore with emphasis on small zooplankton and micro invertebrates

- Breeding: Daily spawner with adhesive eggs placed on plants or mops

Tropical Fish Co. Notes

The RLF Red Emperor is a standout medaka for planted aquariums and patio tubs. Saturated red coverage shows beautifully in top view and side view, which makes this line a compelling display fish for small water gardens and nano tanks. Give them bright natural light or a full spectrum LED, calm surface water with floating plants, and a varied micro diet, and they color up quickly. They mix well with other gentle ricefish lines and small community species that share similar water and flow needs. If steady spawning is the goal, use a slightly longer day length, provide soft mops or fine plants, and move eggs to a hatching container for consistent high yield.