European Bitterling, Rhodeus amarus
The European Bitterling (Rhodeus amarus) is a temperate freshwater fish belonging to the Acheilognathinae sub-family of the Cyprinidae family. It originates from Europe, ranging from the Rhone River basin found in France to the Neva River found in Russia. It was originally described as Cyprinus amarus by Marcus Elieser Block in 1782, and has been referred to within scientific literature as Rhodeus sericeus amarus. It’s known simply as “the bitterling” within its native range, where it is the only species of its genus Rhodeus, and occasionally in the scientific literature as well. But this is technically incorrect, being a leftover from the times where the European Bitterling was united with its Siberian relative, the Amur Bitterling, in R. sericeus. Properly, the term “bitterling” can refer to any species of Rhodeus.
This fish achieves a size of up to 4 inches. It can be found among plants over sandy and muddy bottoms within shallow waters. It consumes mainly plants, and to a lesser extent upon worms, insect larvae, and crustaceans.
This species was once utilized for human pregnancy tests. Female specimens were injected with the urine of the woman to be tested. If the woman was pregnant, the hormones in the urine would cause the fish’s ovipositors to stick out.
The bitterling spawns in clear and slow running or still water, often with a muddy bottom. The female fish deposits her eggs inside freshwater mussels. The male sheds his sperm into the inhalant current of the respiring mussel and thereby fertilizes the eggs. The young hatch and stay protected within the mussel for about one month, eventually leaving the mussel as actively swimming larvae. Both the males and the females achieve sexual maturity in one year, at a length of 1.1 to 1.4 inches.
Image Caption: European Bitterling, Rhodeus amarus. Credit: George Chernilevsky/Wikipedia