Oryzias latipes - Japanese Rice Fish - Medaka
by Jacklyn McNaughton
From "Fins & Friends" Regina Aquarium Society, Canada
Aquarticles.com
These fish can be found in east Asia - Japan, China, and South Korea. They are a
peaceful fish, suitable for a well planted community aquarium, if the tank mates are not
large.
As a rule the males are more slender and their anal fin is larger and ends more
pointed. The colouration is more intense. They will grow to a size of about 2 1/4"
(5.5cm).
They like medium to hard water (10-15 degrees dGH) pH of 7.0 and a temperature of 64
-75 degrees F (18-24 degrees C). They like aeration and water movement. The water should
be clean.
I knew very little about rice fish when I purchased a trio of two females and one male.
They were placed into a small three gallon tank with the temperature and water
requirements as mentioned. I placed in the breeding tank a sponge fry filter and a wool
mop. At the same time I also set up a tank for hatching the eggs.
I gave the fish a few days to become accustomed to their new home; then every 2-3 days
I removed the wool mop and squeezed it out. Sure enough, I always found 4-8-10 eggs clear
as glass. I picked them out, attached them to a small piece of Java moss and placed it in
the rearing tank. After a week or so I had over 80 eggs. The eggs hatched in 10-12 days. I
kept a record of how many eggs I transferred and the dates. After 10 days I found one
small fry, them 3 and finally 5. I wondered why only 5 hatched out of 80 eggs.
Because I like to experiment, I set up another three gallon tank with RO water - pH
7.0, a fry filter, and kept the temperature around 80 degrees. I again gathered eggs for
another week and retrieved another 80. After 10 days I began seeing fry, and after a
couple of days I counted over 30 fry. Now I was satisfied.
Now during this time, as mentioned, I knew very little about these fish. I noticed one
female had a string of eggs stuck to her bottom anal fin. I was shocked and wondered if
this was normal, or maybe she had a problem and couldn't get the sticky eggs off. So on
two occasions I caught her in a small net and gently removed the eggs. On placing her back
into the tank, she appeared to be unconcerned with what I had done. The eggs I placed into
the rearing tank.
Then luckily I received a new reference book. I learned that the female may continue to
carry the eggs in a bundle in front of the anal fin. The eggs are linked together in a
grape-like cluster and will be brushed off on plants, etc. Now I knew it was perfectly
normal for the eggs to be attached to the female. Problem solved - I was only trying to
help.
The fry have survived and grown and have been easy to raise. With each water change I
have added hard water and they are still content and growing. They have been fed dry
sifted fry food and later live brine shrimp.
I was pleased to have the chance to breed these fish because we learn something new
each time. Now with a little more knowledge and experience we can carry on and try
something new again.
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