Oryzias latipes – Japanese Rice Fish
Oryzias latipes, also known as the Medaka or Japanese Rice Fish, belongs to the family Adrianichthyidae. The species was first described by Temminck & Schlegel in 1846. The name Oryzias comes from the Greek word ὄρυζα (oryza), which means ‘rice’. This refers to the fact that some members of the genus live in rice fields. The species name latipes comes from the Latin word latipes, which means ‘broad-footed’.
Synonyms
Synonyms for Oryzias latipes include:
Poecilia latipes Temminck & Schlegel, 1846
Aplocheilus latipes (Temminck & Schlegel, 1846)
Oryzias latipes latipes (Temminck & Schlegel, 1846)
This fish species is a fascinating subject of study and has a rich history in both scientific research and the aquarium hobby.
Description
Oryzias latipes has a slender, elongated body, a relatively flat back, and a slightly rounded belly. This fish species has long fins, especially the dorsal (back fin) and anal fins. Males often have elongated rays in these fins. They grow to a maximum length of about four centimeters
Color
In the wild, Japanese rice fish are usually off-white to silvery in color. However, many selectively bred color variants are available, such as orange, gold, black, pink, albino, and even transgenic ‘glow’ variants that can light up in different colors. These latter colors are banned in Europe.
Sexual Dimorphism
Differences between the sexes: Males are usually slimmer and have elongated rays in the dorsal and anal fins. They are often more colorful than females. Females are generally slightly larger and have a fuller belly, especially when carrying eggs. They have a less pronounced fin structure compared to males.
Differences between Juveniles and Adults
Young fish are smaller and have not yet developed the full color and fin structure of adult specimens. They are often less colorful and have shorter fins. Adult fish have developed the full color and fin structure. Males often display more pronounced colors and elongated fin rays.
Behavior and Temperament
Oryzias latipes is generally a peaceful fish species that can be kept well in groups. They are not aggressive and usually do not exhibit territorial behavior. These fish live in schools and feel most comfortable in groups of eight or more.
They are not particularly shy or skittish, but they can hide if they feel threatened. They usually swim in the midwaters of their habitat and are not specifically bound to the bottom or the surface.
Lifespan
The average lifespan in the wild is about 2 years. Under good conditions, they can live 3 to 5 years in an aquarium.
Habitat of Oryzias latipes (Japanese Rice Fish)
Oryzias latipes naturally occurs in East Asia, particularly in Japan, Korea, China, and Vietnam. In Japan, the species can be found on the islands of Honshu, Shikoku, and Kyushu, and has been introduced to Hokkaido. The species has also been observed in Laos, Taiwan, and parts of China.
This fish species mainly lives in shallow waters such as rice fields, ponds, marshes, slow-flowing rivers, and tidal pools. They prefer waters with a depth of about 30-60 centimeters.
They are found in the river basins of the Nam Theun, Mekong, Irrawaddy, Salween, Red River, and Nanpangjiang.
Their natural habitat often consists of waters with a lot of vegetation, which provides hiding and breeding places for the fish. The bottom of their natural habitat often consists of mud or sand.
Oryzias latipes lives in a temperate to subtropical climate and is subject to seasonal temperature fluctuations. They can survive in both fresh and brackish water. The natural breeding season of Oryzias latipes runs from mid-April to the end of September. They can experience periods of flooding, especially in rice fields and marshes during the rainy season.
Diet
In their natural habitat, Oryzias latipes are omnivores and eat a wide range of food sources. Their diet mainly consists of:
- Small insects: They feed on various types of small insects found at the water surface.
- Worms: They also eat small worms present in their environment.
- Crustaceans: Small crustaceans such as Daphnia and Artemia are also part of their diet.
- Zooplankton: They consume other forms of zooplankton present in their habitat.
- Biofilm: They feed on biofilm and other microorganisms growing on surfaces in the water
In an aquarium, Oryzias latipes can be fed a variety of foods to mimic their diet in the wild and promote their health:
- Dry food: They accept dry food such as flakes and granules.
- Live and frozen food: It is recommended to regularly give them live or frozen food, such as Daphnia, Artemia, finely chopped red and black mosquito larvae, and fruit flies.
- Supplements: For optimal health and reproduction, small food items such as small worms (Grindal worms) and other small insects can be added.
The Aquarium
For a group of Oryzias latipes, an aquarium with dimensions of at least 45 x 30 cm is recommended. This is sufficient for a group of 5 to 6 fish. If you want to keep more, a larger aquarium is recommended.
The Aquarium
A heavily planted aquarium is ideal, with dense vegetation and some open areas. Floating plants are also appreciated as they dim the light and mimic a natural environment. Preferably use a dark substrate. This enhances the colors of the fish. Some wood or roots among the plants can provide extra hiding places and also mimic their natural environment.
Water parameters
The temperature should be between 16 and 22 °C. They can tolerate a wide temperature range, but prolonged exposure to higher temperatures can shorten their lifespan. The pH should be neutral to fairly high, with a pH between 6.5 and 8.5.
In well-insulated homes, the aquarium can be kept without heating, as long as the room temperature remains within this range.
Suitable Tank Mates
Oryzias latipes is a peaceful fish that gets along well with other small, peaceful species that prefer similar water conditions. Suitable tank mates include:
- Chinese Danio (Tanichthys albonubes)
- Rasbora Galaxy (Danio margaritatus)
- Rosy Loach (Yunnanilus sp. ‘Rosy’)
- Brachygobius gobies (brackish water)
- Panda Garra (Garra flavatra)
- Dwarf Botia (Ambastaia sidthimunki)
- Nerite Snails
Breeding aquarium and conditioning
Oryzias latipes can be bred in both a regular aquarium and a special breeding aquarium. For a special breeding aquarium, a volume of about 20 to 40 liters is recommended. The water temperature should be between 16 and 22 degrees Celsius. Set up the aquarium with plenty of fine-leaved plants like Java moss or breeding mops.
It is not strictly necessary to temporarily separate the males and females, but it can help stimulate breeding. When you are ready to breed, you can transfer one or more pairs to the breeding aquarium. If you use a breeding group, a ratio of one male to two females is ideal to reduce competition between the males and increase the chances of successful fertilization.
During the breeding period, the males become darker in color and defend small, temporary territories against each other while trying to attract the females. This intensification of color is a sign of their readiness to mate and their attempt to attract the attention of the females.
The spawn
Spawning usually takes place in the early morning, often when the first rays of sunlight reach the aquarium. This is a natural behavior also observed in the wild.
The eggs are laid on fine-leaved plants such as Cabomba, Ceratophyllum, or Taxiphylum species, but synthetic breeding mops or other artificial alternatives also work well. The eggs are relatively large and sticky and initially remain attached to the female’s genital opening before being placed on a plant or breeding mop. They are expelled as a single mass and fertilized.
Females can produce a cluster of eggs every few days or even daily when in good condition.
Raising the fry
The eggs of Oryzias latipes have an incubation period that is highly dependent on the temperature. Generally, the eggs hatch within 10-14 days. Once the fry hatch, they begin to swim freely almost immediately.
There is no parental care in Oryzias latipes. The adult fish usually ignore the eggs, but they can eat the free-swimming fry if given the chance. Therefore, it is important to separate the eggs or the fry from the adult fish to increase their chances of survival.
First Food for the Fry
Once the fry start swimming freely, they can be fed microworms, Artemia nauplii (baby brine shrimp), and finely ground food specially made for young fish. It is important to feed the fry small amounts of food several times a day to support their growth.
Water Changes and Survival Rate
It is recommended to regularly change the water to maintain high water quality. This can be done, for example, every other day by changing about 50% of the water. The exact survival rate of the fry can vary, but in a well-maintained and densely planted aquarium, many fry can survive. However, it is important to separate fry of different ages, as older fry can eat the younger ones.
Conclusion
Oryzias latipes is a versatile and easy-to-care-for fish species suitable for both beginners and experienced aquarists. They have no special requirements regarding water conditions and are peaceful, making them well-suited for a community aquarium. Regular water changes and a varied diet are important for their well-being. Their adaptability and interesting breeding behavior make them a fascinating addition to any aquarium.
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Author
John de Lange
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