Danube Bleak
Chalcalburnus chalcoides (Guldenstadt, 1772)
Alburnus chalcoides danubicus (Guldenstadt, 1772): Kovatcheff, 1923: 79.
Order Cypriniformes
Family Cyprinidae
Conservation status: in Bulgaria: Endangered EN [B1a, b]; International: IUCN [DD], BeC-III, HD-II.
General distribution. In Europe - from Austria to Kazakhstan, in the rivers from the basins of the Black Sea, the Sea of Azov, the Caspian Sea and the Aral Sea. It is also found in Greece, in some lakes affiliated to the Aegean Sea basin.
Distribution and abundance in Bulgaria. The species was first recorded in the Iskar River [1]. Later, it was recorded in the Danube River and the lower reaches of some of its tributaries: Iskar, Vit, Osam and Yantra [2, 3, 4, 5, 6], as well as in Srebarna Lake [7]. It was also found in most of the Black Sea rivers [3, 4, 8, 9] and in some coastal lakes: Durankulak, Beloslav, Burgas, as well as the Mandra Reservoir [3, 4, 8, 10, 11]. Recently, its occurrence has been confirmed only in the rivers Sredetska, Fakiyska, Ropotamo, Karaagach and Veleka [12, 13, 14]. Its abundance and biomass in the rivers Sredetska, Fakiyska and Veleka are comparatively low [12, 13]. The species disappeared from Durankulak Lake [15], and its population in Srebarna Lake diminished [16]. At present, it is extremely rare in the Danube River [our data], and its population in the Burgas Lakes has declined in comparison with the past [S. Mihov, unpublished data].
Habitats. The species is mainly found in permanent rivers, but also in estuaries, coastal brackish and fresh water lakes, and in permanent fresh water marshes.
Biology. It has semi-anadromous and non-anadromous forms. The former stay in the lower reaches and river mouths for feeding, and migrate upstream for spawning. The spawning lasts from May to June. The fecundity of the females ranges between 15 000 and 25 000 eggs. The species feeds on zooplankton, different insects and small fish. It reaches a length of up to 40 cm and an age of 6-7 years [17].
Similar species. The bleak (Alburnus alburnus), from which it can be differentiated by the higher number of scales in the lateral line (57-86) and the presence of a keel, covered with scales behind the pelvic fins.
Negative factors. Water pollution and increase of eutrophication; intensive recreation development along the Black Sea coast; direct competition from introduced fish species; poaching.
Conservation measures taken. The species was listed in the Red Data Book of Bulgaria (1985).
Conservation measures needed. Protection of lower and middle reaches of the Black Sea rivers against pollution. Introduction of a ban on fishing of the species in the Danube River and the Burgas lakes.
References. 1. Drensky, 1921a; 2. Kovatcheff, 1923; 3. Drensky, 1943; 4. Drensky, 1951; 5. Karapetkova, 1972; 6. Marinov, 1978; 7. Bulgurkov, 1958a; 8. Chichkoff, 1934; 9. Karapetkova, 1976; 10. Drensky, 1923; 11. Gheorghiev, 1967; 12. Dikov et al., 1994; 13. Dikov, Zivkov, 2004; 14. Trichkova et al., 2006; 15. Vassilev, 1999; 16. Pehlivanov, 2000; 17. Karapetkova, Zivkov, 1994.
Authors: Tihomir Stefanov, Teodora Trichkova
