UDC: 597.551.2+597.556.331.1](497.6) original scientific paper Acta Agriculturae Serbica, Vol. XIV, 27 (2009) 23-33 Ecologial Characteristics of the Roach (Rutilus rutilus L.) and Bream (Abramis brama L.) in the Reservoir of the Lake Modrac A. Adrović School of Natural Sciences Tuzla, Bosnia and Herzegovina R. Škrijelj School of Natural Sciences in Sarajevo, Bosnia and Herzegovina I. Skenderović School of Natural Sciences Tuzla, Bosnia and Herzegovina Abstract: A one-year study on the fish population of the Modrac reservoir showed that roach (Rutilus rutilus Linnaeus, 1758) and bream (Abramis brama Linnaeus, 1758) predominated in the ecosystem, roach being a dominant and bream a subdominant species. That was the very reason for this research aimed at examining their ecological characteristics, gender, age structure and growth. The analysis included 345 samples of roach and 216 samples of bream. It was conducted separately for each gender of both species. Key words: ecological characteristics, roach, bream, Modrac reservoir Introduction Lake Modrac is an artificial lake formed in 1964 for the purpose of supplying the industry of Tuzla with water. At the time of its construction, the length of the reservoir was about 11km, the breadth about 1.6km and the surface area about 17.10km², with the depth of about 18 m and an average depth of about 6m (Mihaljevic et al. 1997). Throughout its existence, the lake has been exposed to intensive alluvium covering from shore abrasion and high amounts of coal dust from