The Care and Keeping of Japanese Rice Fish

oftThe October 2018 issue of the Amazonas magazine featured “Marvelous Medaka”, or Japanese Rice Fish on the cover. This article inspired me to obtain a group of 6 of these fish. The species, Oryzias latipe, has been kept in Japan for literally hundreds of years. But other than the magazine article that triggered my interest, I could find very little English language information on this fish. In this article, I’ll lay out the basics of their care and keeping.

In Japan, Rice Fish are mainly kept in small tubs or outdoor ponds. Thus, the fish are mostly viewed from above rather than from the side like American aquarists are generally used to. This subtle difference should be kept in mind when setting up your own Medaka environment. I can’t remember the source, but I heard that Medaka in Japanese means “light from within”, a reference to a sort of translucent reflection of light off the internal organs of these fish.

Medaka are an easy fish to keep. They are tolerant of an extremely wide range of temperatures, from the low 60’s to 90F. They like clean water, but will tolerate going for times with out water changes. Water hardness and pH do not seem to be critical factors. Even though some Japanese are able to keep them outside on rooftop tubs, we should give them the best care possible.

Shortly after becoming interested in these fish, I came across on online outlet that had groups of Japanese Rice Fish – Youhiki for sale. These were rice fish with a yellowish to orange coloration. I had great trust in the vendor so I immediately purchased a group.

When I brought the fish home, I placed them in an unheated, 10 gallon aquarium. This tank stays at 70F more or less. The water was city water. I kept a cover on the tank as Rice Fish are know to be jumpers. Initially the tank had a clump of Java moss as well. I fed the fish regular flake food, and Ken’s premium growth food. The growth food comes in very small granules and floats, much to the liking of the Medaka.

Medaka have an interesting breeding strategy. The female will carry eggs in her pectoral fins for several hours. This could be as few as 5 but as many as 40 for a mature female. Eventually, she will swim into some dense plant material and the sticky eggs are left behind. Medaka in good condition will spawn every day.

In Japan and Europe, many colors and “styles” of Medaka can be found. Colors can be white, yellow, red and sometimes blue. But also, some Medaka can exhibit reflective spots. The picture below shows these spots quite well. Americans not familiar with Medaka may mistake the spots for ich. But in fact, it is quite desirable in some strains. Breeders of these strains will attempt to perfect symmetry from left side to right side when viewed from above.

After first seeing the egg carrying behavior, I removed the Java moss and placed 2 yarn spawning mops in the tank, one on the bottom and one floating. Both seemed to work equally well so I discontinued the sinking mop as the floating mop is easier to retrieve. Thanks to advice from other Medaka keepers, I would leave the mops in the tank for 5 days or so, then pick the eggs off. I placed the eggs in deli containers. I checked on the containers daily, removing any swimming fry to a 2.5-gallon tank. The fry naturally come to the surface and are easy to capture with a small shot glass. Once in the fry tank, I would feed Hiakari First Bites twice per day. As individual fry reached about ½ inch long, I moved them to a 10 gallon grow out tank. Using this simple approach, I’m able to breed hundreds of these fish.

Medaka are enjoyable and easy to keep fish. I look forward to having some in tubs outside over the warm months. If I have an opportunity to purchase more red or koi-like variations, I definitely will.

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