The bitterling is a type of fish that belongs to the cyprinid family. It can be identified by the scientific name rhodeus. This coldwater fish is native to the streams of Europe, though it has since been introduced to North America. Bitterlings include more than a dozen different species, the most common being rhodeus amarus, or the European bitterling.
Bitterlings are silvery violet in color with a barely noticeable blue stripe running horizontally down the body. During breeding season, typically from April to June, the male will develop brighter colors. He displays a reddish tint to his fins as well as his belly at this time. Bitterlings average between two and three inches (5 and 7.5 cm) in length.
The most distinctive characteristic of the bitterling is its unique method of breeding. The female of the species extends a small tube, called an ovipositor, from her body for egg laying. This allows her to lay her eggs inside the gill filaments of a freshwater mussel, which will act as a host for the fish eggs. The male then releases his sperm just outside the mussel. When the mussel inhales the water, the eggs are fertilized and will develop and hatch within the gills of the host.
It is believed by some that bitterlings may be able to predict pregnancy. When introduced to the urine of pregnant women, the females of this species developed their ovipositors. This study has been refuted, however, and many people believe that the fish respond similarly to urine from women who were not pregnant as well to urine from from men.
This fish is often kept in aquariums or decorative ponds. It prefers a temperature somewhere between 55 and 72 degrees Fahrenheit (13 and 22 degrees Celsius). The best water chemistry for this type of fish is slightly alkaline. An area with plenty of open swimming space as well as ample vegetation is ideal. While the bitterling can survive in outdoor ponds, it should not be left outdoors through the winter season in climates where the water will freeze over.
These are omnivorous fish, and as such, consume a wide variety of foods. Standard flakes or pellets should be supplemented with other items. This fish will eat most small invertebrates, and prefers live food. Algae and other vegetation can also be provided for supplemental nourishment.