For this study which is done in 2008-2009,140 Caspian salmon (Salmo trutta fario) fish were grows condition, in Lar Reservoir Lake. During the study, some biometric specification such as length, weight, age, gonad weight and condition factor of Fulton and Clark in both sexes were examined. The male fish in the water source (85 samples), with total body length 15 to 32.6 cm, Fork length 14.3 to 31.9 cm and body weight 40 to 451.3 gr. Body weight without offal 29 to 393.3 gr, and Fulton index 0.84 to 1.60 to Clark 0.68 to 1.35, absolute weight of gonad 15 to 28.03 gr. Weight of gonad respectively was 0.17 to 12.56 per cent of body weight. And ages 2 to 6 years were variable. Lar female fish of water source (55 sample), with total body length 14.2 to 46.2 cm, Fork length 13.7 to 44.8 cm, body weight 28.6 to 893.94 gr, body weight without offal 25.0 to 762 gr, Fulton index 0.89 to 1.56, Clark index 0.74 to 1.19, the absolute weight of gonad 0.08 to 59.86 gr, the respective weight of gonad 0.12 to 20.03 body weight, absolute fecundity 119 to 1088 eggs, Age 2 to 7 years were variable. Gonad fish maturity whether in male or female in this study were between 2 to 5. By the Kruskal-Wallis test, Fulton index values between the two sexes, male (1.26±0.01) and female (1.21±0.02) and also in Clark index between two sexes male (1.06±0.02) and female (0.99±0.01) statistical differences were observed (p<0.05). In terms of physiology and histological study, Gonad fish in the months of September and October showed that the stages of maturation was in steps 4 and 5, which indicates that the migration reproduction is in the upper parts of the river. T-test Statistical differences in indices such as body weight, Fork length of male and female fish at different ages didn’t show (P>0.05). But the variance analysis differences between the male and female from the perspective of indices absolute and respective weight of gonad were showed (p<0.05).