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Last updated on April 24, 2014 at 5:50 EDT

Rosy Bitterling, Rhodeus ocellatus kurumeus

Image Caption: A Japanese rosy bitterling, taken in Japan, 2006. Credit: Book 74/Wikipedia (CC BY-SA 3.0, 2.5, 2.0 and 1.0)

The rosy bitterling is a fresh water fish native to Japan consisting of two distinct species, the R. o. kurumeus and the subspecies R. o. ocellatus. The R. o. kurumeus species of this fish is found only in Japan, whereas the R. o. ocellatus species is also found in China and Taiwan. Both species inhabit small ponds, reservoirs, and creeks.

The original species of the fish was the R. o. kurumeus and it was widespread on the western side of Japan. In 1942 this fish was accidentally introduced with grass and silver carp. With interbreeding the R. o. ocellatus of this species was born. Since then, the R. o. ocellatus has increasingly gained in population, whereas, the R. o. kurumeus has decreased in population and is now on the endangered species list as critical of becoming extinct.

These two species of rosy bitterling are very similar but have distinctive differences. The R. o. ocellatus has silvery-white lines on the ventral fin; the R. o. kurumeus ventral fin is darker with no lines. The size comparison between these two species of rosy bitterling is another difference. The R. o. ocellatus are larger with the male growing over 3 inches and the female will reach 2.5 inches. The R. o. kurumeus is much smaller, the male will seldom reach 2.5 inches, and the female will average around 1.75 inches. The bodies of both species of the rosy bitterling are flat and silver colored. Lifespan of this fish is rarely over three years.

During the spawning season from March to September, the male will turn reddish or purple to attract a female. The female rosy bitterling has a pipe usually the same length as the body used for laying eggs. Normally, 2 – 3 eggs are laid at one time at the gill of a fresh water mussel. After the female has placed the eggs, the male will fertilize them. Usually this process will occur daily in 6 – 9 day intervals, around ten times in a spawning season.

The eggs will grow in the mussel gill and hatch in 3 days. After hatching, the juvenile rosy bitterling will stay inside the mussel gill for 15 – 30 days. The juvenile will swim from the mussel when it reaches .3 inches in length. Within one year the rosy bitterling will grow to its adult size.

Conservation measures have been in place for the R. o. kurumeus, to help protect this species. But, pollution, water conditions, and the number black bass and bluegill within the same water body, this species population is still in decline.

Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Cypriniformes

Family: Cyprinidae

Rosy Bitterling Rhodeus ocellatus kurumeus