21 Dec The most beautiful fish of the Nida river
The bitterling fish is the smallest carp in Europe, it grows up to 11 centimeters. During the mating season it is easiest to distinguish between the male and the female. The male’s fins are reddish-pink at that time and a characteristic stripe running through the center of the body appears. In the females, for a change, a so-called ovipositor is formed, i.e. a tube about 5 cm long, through which the female lays an egg inside a mussel, e.g. the swan mussel or the river mussel.
From the end of April to July the female lays 20 eggs in the mussel’s gill hole. During the breeding season, the males mark territories of up to 80 cm, where several mussels can be found. The males compete with each other for territory, starting the mating dance, which aims to indicate the female mussel. The female checks if the given mollusk is a good “guardian”. This mussel is “tamed” by the fish. After 40 days, fish are born, 8 mm in size.
In the 1990s, scientists often found the bitterling fish in the Nida river and then its numbers fell from year to year. The presence of this fish in a given body of water is connected with the presence of mussels. As the pollution increases, mussels disappear, and bitterling fish also disappear.