In this research, morphological and histomorphometrical structure of testis of 20 silver male carp fish were studied in two classes or groups. Group1 was composed of 10 fish with average (±SD) weight of 1.247+0.656kg and average(±SD) length of 43.675+1.414cm with about 2 years age, Group2 was composed of 10 fish with average(±SD) weight of 5.716+0.519kg and average(±SD) length of 81.5+1.643cm. Average (±SD) weight of testis were 2.34+1.47gr and 83.33+25.81gr with average (±SD) GSI of

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... and 1.457+4.974 in groups 1 and 2 respectively. Samples from testis were taken by maximum thickness of 0.5cm and after fixation in bouin,s fixative and 5-6µm thickness section were made routine paraffin embedding method and stained by Hematoxylin-Eosin and PAS staining. The microscopic results showed that the silver carp testis was lobular and cystic type in two groups. In group 1, there was no spermatozoon activity and PGCs were only germ cells in the cysts. But in group2, the numbers of PGCs were decreased significantly and spermatogenic cells were seen in different phases including spermatogonia, primary and secondary spermatocysts, early and late spermatid, and spermatozoa which each one was located in a separated cyst. There was no significant difference in nucleus diameter of PGCs in testis of group1 (6.97+0.438µ) and group (6.13+0.438µ). In group2, the nucleolus diameter of spermatogonia was 2.97+0.112µm, primary spermatocyt 3.59+0.107µ, early spermatid 1.59+0.761µ, late spermatid 1.24+0.132µ, spermatozoa 1.16+0.054µ, and the length of spermatozoia 17.412+1.946µ. The interesting finding was immature testis in fish of group 1 with average weigh (1.247+0.656kg) and average length (43.675+1.414cm) in about 2 years age and mature testis in fish of group 2 with average weight of (5.716+0.519kg) and average length of (81.5+1.643cm) with about 4 years age in Khuzestan climate conditions.