Romanogobio kesslerii (Dybowsky, 1862)
Gobio similis Chichkoff, 1929: Chichkoff, 1929: 158; Gobio carpathorossicus Vladykov, 1925:Drensky, 1930: 669; Gobio kessleri Dybowski, 1862: Chichkoff, 1937: 267; Drensky, 1951: 86; Karapetkova, Zivkov, 1995: 118.
Conservation status: in Bulgaria: Endangered EN [B1a, b (i, ii)]; International: IUCN [DD], BeC-III.
General distribution. In the basins of the rivers Danube, Dniester and Vistula. It is found in Austria, Bulgaria, Moldova, Poland, Romania, Russia, Slovakia, Slovenia, Serbia, the Ukraine, Hungary, Croatia and the Czech Republic. It is also found in the rivers Vardar, Aliakmon and Pinios flowing into the Aegean Sea.
Distribution and abundance in Bulgaria. It was recorded in the Danube River  and the middle reaches of most of its tributaries: Nishava, Archar, Lom, Ogosta, Iskar, Vit, Osam, Yantra and Rusenski Lom [2, 3, 4, 5, 6, 7, 8, 9, 10, 11]. In recent years, it has been a rare species with declining abundance and range size; it has been found only in the basins of the rivers Lom, Iskar, Vit and Yantra [12, our data].
Habitats. It inhabits mainly the middle reaches of permanent rivers with sandy and gravel bottom.
Biology. A benthic reophilic species. It lives in shoals of several tens of individuals. It reaches sexual maturity in the second year. The spawning lasts from the middle of May to September. The fecundity of females ranges between 2 000 and 3 000 eggs. It feeds on benthic invertebrates, diatoms and detritus. It reaches a maximum length of 129 mm and an age of 6 years .
Similar species. The gudgeon (Gobio gobio), the white-finned gudgeon (Romanogobio albipinnatus) and the Danubian longbarbel gudgeon (R. uranoscopus), from which it differs by the presence of 8 soft rays in the dorsal fin.
Negative factors. Fluctuations in river discharge as a result of river regulation activities; deforestation (especially in the mountain regions); water pollution.
Conservation measures taken. None.
Conservation measures needed. Restriction on the regulation activities and micro-hydro power development in the upper and middle reaches of the Danube tributaries; control of deforestation in the mountain regions; protection of the rivers against pollution.
References. 1. Marinov, 1978; 2. Chichkoff, 1929; 3. Chichkoff, 1937; 4. Chichkoff, 1939; 5. Drensky, 1951; 6. Bulgurkov, 1958; 7. Michailova, 1972; 8. Dikov et al., 1988; 9. Michailova, 1970; 10. Karapetkova, 1972; 11. Karapetkova, Undzian, 1988; 12. Dikov et al., 1994; 13. Banarescu, 1999.
Authors: Tihomir Stefanov, Teodora Trichkova