Animal-World > Aquarium Tropical Fish > Killifishes | Tooth Carps | Pupfishes | Topminnows > Japanese Rice Fish - Medaka

Moonlight Medaka

Japanese Rice Fish - Medaka

Family: AdrianichthyidaeOryzias latipesPhoto © Animal-World: Courtesy Ken Childs

   Of all the Japanese Rice Fish colorations, a school of Moonlight Medakas is one of the most eye catching attractions in the aquarium!

   The Japanese Rice Fish or Medaka have been popular aquarium fish for many years, since the 17th century in Japan. They are 'amphidromous' meaning they are fish that move between fresh and salt water during some part of their life cycle. The wild version of this fish is not particularly attractive. Fortunately for the aquarist, there are a few selectively bred colors varieties that are quite attractive and well worth keeping in the home aquarium.

   The Japanese Rice Fish or Medaka comes in many colors. The Moonlight Medaka is a shiny silver color morph that is a relatively new addition to the aquarium hobby. These are genetically enhanced versions of this fish that contain a sea jelly gene that causes them to glow under a black light. The best known version is the Gold Medaka (gold color morph), which has been around for hundreds of years. The Moonlight Medaka is a very sturdy fish that can live in warm or cold water. This cold water tolerance also makes it a good choice as a pond fish.

For more Information on keeping freshwater fish see:
Guide to a Happy, Healthy Freshwater Aquarium

Geographic Distribution Oryzias latipes Data provided by FishBase.org Scientific Classification Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Beloniformes Family: Adrianichthyidae

Distribution:    The Japanese Rice Fish or Medaka was described by Temminck and Schlegel in 1846. They are naturally found in Japan, Korea, China and Viet Nam where they inhabit slow moving waters. They have also been introduced in Iran and Turkmenistan.
   The Moonlight Medaka is a color morph of the Japanese Rice fish, and is not found in the wild. NOTE: The Japanese Rice Fish or Medaka are used extensively for scientific research. More information on this subject can be found here, on the Medakafish Homepage.

Status:    The Japanese Rice Fish or Medaka fish is not listed on the IUCN red list. There are no wild populations of the Moonlight Medaka.

Description:    The body of the Japanese Rice Fish or Medaka is slender and elongated with a slightly arched back. The wild form of this fish is not particularly flashy, being a rather bland cream color but with some iridescent blue-green flecks. It does have beautiful large almost luminescent eyes. The wild strain is seldom seen in the aquarium trade.
   The Moonlight Medaka and the Gold Medaka are captive bred color morphs. They are fluorescent ornamental varieties, genetically modified fish that glow under a black light. They were developed by attaching a product of fluorescent protein extracted from jellyfish into embryonic Japanese Rice Fish. The Gold Medaka has been around for hundreds of years, while the Moonlight Medaka is a relatively recent development.

Size - Weight:    This fish will reach 1.6 inches (4 cm).

Care and feeding:    The Moonlight Medaka will eat all types of foods, including flake and freeze-dried foods.They will also eat smaller prepared or frozen foods, so feeding is not a problem.
   They are an easy fish keep and are a great choice for unheated or small aquariums. Tanks mates should be of a similar size and should be non-aggressive. They will appreciate a well planted aquarium and they like aeration with good water movement. They also need filtration for clean water.

Water Region: Top, Middle, Bottom:    The Medaka will swim in most parts of your aquarium.

Acceptable Water Conditions:    Temperature: 64 - 75° F (18 - 24° C)
   Hardness: 9 - 19° dGH
   Ph: 7.0 - 8.0

Social Behaviors:    The Moonlight Medaka are very peaceful, great for a community tank with other peaceful fish of similar size.

Sexual Differences:    Sex is not always easy to determine but males tends to be more slender. The dorsal and anal fins of the males are also larger than those of the females.

Breeding/Reproduction:    The Medaka can be placed in a breeding tank with fine leaved plants or a spawning mop. They can be introduced to the tank as a pair or in a small school. Spawning usually occurs at dawn. After the eggs are fertilized by the male, many of them will remain attached to the females belly.. As she swims around and comes into contact with water plants, the eggs will detach from her belly and will be attached to the plants. The eggs will hatch in 10 to 12 days. The newly hatched fry should be fed infusoria, a liquid fry food, or newly hatched baby brine.

Availability:    Though the Moonlight Medaka are commonly available, the genetically altered versions of the Japanese Rice Fish are not legal in some U.S. states. They will run about $.80 to $2.00 each.

Author: Ken Childs
Additional Information: Clarice Brough, CFS

Lastest Comments on Japanese Rice Fish - Medaka View all 4 comments on Japanese Rice Fish - Medaka Add Your Comment

Bill Greig - 2011-06-03 I had a schoal of 20 blue eyed medaka. The tank got overgrown with one of the plants, a fine leaved weed. Suddenly the top was alive with tiny fry: I netted c 8 int a sidetank; feeding them with liquifry, and finely ground fish fkake ( Mortar and pestle) They do not seem to be growing a week in: is this normal?? Click For Replies (2) Charlie Roche - 2011-06-03 For the Rice Fish Animal World recommends "The newly hatched fry should be fed infusoria, a liquid fry food, or newly hatched baby brine". Also, realize these are not big fish and it is hard to determine if they are growing and at what rate. Try th baby brine as you are already doing the liqufry. Good luck and let us know what is happening. Honest. Alex Burleson - 2012-01-09 Yes, depending on the water quality, and how much food they're being fed they may not grow as expected. As you stated, it has been a week, so simply be patient. Fish are quite exciting, but do require a great deal of patience. Additionally, you could try feeding them baby brine shrimp. Simply research how to breed/harvest them. Reply

Bill Greig - 2011-07-17 Further, to my last the group of small fish are growing, but every few days I see 2 or 3 more threadlike fry, in the tank: 9 fry have increased to 12: WITH NO ADULT FISH PRESENT. I urgently need to be told by an expert in the medaka field what is happening: success is nice, but what have I got here??? Click For Replies (2) Charlie Roche - 2011-07-18 You must some some adult fish without. The only other thing I can think of is you brought in additional plants and eggs had been depositied on the plants and they take 10 - 12 days to hatch. chin7602 - 2011-12-08 My Medaka were 40.after 1 week I saw there were 90 Reply

Bob Meyer - 2011-12-06 A few years ago, I had hundreds of gold medaka rice fish. Oryzias latipes. Then I lost them and most of the fish in the fish room during an ice storm last year. If anyone has a lead on a reasonably priced place to buy these, please post a comment! Reply

amanda simms - 2010-07-11 This is the best information ever! Thanks a lot! Reply

Add your comment!

View all 4 comments on Japanese Rice Fish - Medaka

Back to Killifishes | Tooth Carps | Pupfishes | Topminnows