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Knowledge of fish diversity, population data and the stock size, and calculation of the amount of proper catch are essential for a wise and sustainable management of lakes. This research reports a study on fish populations in Dorudzan reservoir, Fars Province. The fish were sampled from three stations in the late Summer and mid Spring 2015, three days each, using nylon gill nets. The mean length and optimum length, condition factor, catch per unit effort, total biomass, and acceptable catch were assessed. Fish community of the Dorudzan reservoir were comprised of 8 species Cyprinus carpio, Carasobarbus luteus, Alburnus mossulensis, Capoeta aculeate, C. damascina, Hypophthalmichthys molitrix, H. nobilis, and Paniliza abu, the two last species of which are reported for the first time from this reservoir. The length-weight equations indicate a proportionate growth, except for H. nobilis whose scarce number in the samples did not allow the analyses and assessments. The condition factor was higher than 1 in all species, which confirms their proper somatic growth. The acceptable lengths for catch were calculated for P. abu (14cm), C. carpio (30cm), C. luteus (21cm), A. mossulensis (14cm), C. aculeate (24cm), C. damascina (24cm), and H. molitrix (76cm) and catch per unit efforts were 6324g for P. abu, 1260g for A. mossulensis, 2064g for C. carpio, 800g for C. aculeate, and 172g for C. luteus. Maximum acceptable catch for P. abu, C. carpio, C. luteus, A. mossulensis, and  C. aculeate in Dorudzan reservoir in 2015 were calculated as 12309, 3690, 293, 2643, and 1367 kilograms, respectively. However, according to the higher accuracy of length based assessments, they are recommended to use acceptable lengths for catch in catch regulations. Due to the continuous climate regime change and eutrophication conditions, it is highly emphasized to assess and monitor the fish populations of the lake.