* Japanese name: Ichimonji-tanago
* Scientific name: Acheilognathus cyanostigma
* Description: The bitterling is a small fish, growing to around 70 mm in length. Adults are fairly deep-bodied, with a similar body shape to goldfish. In the breeding season, males become much more brightly colored than females, with broad beautiful iridescent blue and violet stripes on their flanks. Females are a relatively plain silver-gray. The bitterling is in the family of fish called the Cyprinidae, from the Greek word for goldfish. Minnows and carps are also members of this family.
* Where to find them: In ponds, ditches and other lowland bodies of water. Also in Japan's largest body of fresh water, Lake Biwa in Shiga Prefecture, and in some rivers. Bitterlings are hardy fish, and can survive cold water temperatures. Below 10 degrees they enter a sluggish "winter state" of reduced metabolism. However, although they are hardy, they are not invulnerable. Water quality in rivers and lakes in Japan is declining as chemicals used in farming and industry run off into the water, as well as waste products from animals. The environmental degradation means that bitterling numbers have fallen, and the fish is now on the official "Red Data" list of endangered species.
* Food: Bitterlings eat water fleas and planktonic crustaceans. They graze on water plants, removing microscopic animals such as rotifers and small insect larvae. Incidentally, bitterlings themselves do not make very good eating. Their bitter taste is probably a defense against predatory fish such as pike.
* Special features: Females have a remarkable way of ensuring that their eggs develop safely. As can be seen in the picture of the female fish in the background above, they grow a long egg-depositing tube that extends from their genital opening. This tube allows the female to precisely control where she lays her eggs -- which she does directly into the gill chamber of a freshwater mussel. Her mate then releases his sperm over the mussel, which draws it in with the water it takes in to its gills. Once inside, the sperm can fertilize the female's eggs. This way, males don't have to go to the trouble of building a nest and defending it, and can just move on to the next female. Females, meanwhile, can lay nice fat eggs, which will develop safely for 2-3 weeks inside the mussel. The young fish then remain inside their host for a couple of days after hatching and then leave. The mussel is apparently unaffected by the invasion of privacy.
PHOTO COURTESY OF BIO-IMAGE NET
