The objectives of the present study were to compare growth performance and feed conversion ratios of brook trout (Salvelinus fontinalis) and Black Sea trout (Salmo trutta labrax) in monoculture and duo-culture tank reared conditions. The fish were about 9-month-old hatchery reared brook trout and Black Sea trout with initial weights of 24.18 +/- 0.64 (n=60) and 23.87 +/- 1.11 (n=60) g, respectively. Fish were kept in 0.2 m(3) fiberglass tanks. Nine tanks were used and the fish were equally allotted to 3 groups with tree replicates and fed for 240 days. Each tank contained 20 fish from each species for monoculture and 10+10 fish from each species for duo-culture. At the end of the study, mean live weights of brook trout and Black Sea trout increased to 265.47 +/- 17.25 g and 206.18 +/- 2.95 g in monoculture. 235.53 +/- 10.25 g and 222.47 +/- 1429 g in duo-culture, respectively, and significant differences were found among the groups (P<0.01). The highest and lowest specific growth rates were found in brook trout and Black Sea trout in monoculture (P<0.01), respectively. The highest and lowest final condition factors were calculated in duo-culture for brook trout and in monoculture for Black Sea trout (P<0.01), respectively. The feed conversion ratio (FCR) for Black Sea trout was higher than it was for the other groups (P < 0.01).