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Rutilus kutum, is an endemic fish species of Caspian Sea basin that have been introduced to Gheshlagh River basin, more recently. Fish transplantation to a new habitat may have affected the reproductive characteristics of fishes. To understand the reproductive characteristics of transplanted Caspian Kutum to Gheshlagh River basin, twenty male Caspian kutum specimens with average 2.1 years old were caught from Gheshlagh Dam Lake during April to May 2015 by cast net. Some spermatological characteristics; sperm volume, duration of mobility, sperm density, spermatocrite, pH and osmolarity were measured for all sperm samples. The mean values (±sd) for these spermatological characteristics were 2.41 ± 0.16 cc, 42.46 ± 1.07 sec, 17.31 ± 2.24 million cells/ ml, %40.8 ± 2.34 and 282.1 ± 4.87 mOsmol/Kg, respectively. The mean gonadosomatic index was 5.71 ± 0.31. Na+ (190.87 mEq/l), Cl- (124.60 mEq/l) and K+ (28.34 mEq/l) were predominant ionic concentrations in the seminal plasma. The concentrations of aspartate aminotransferase (AST), alkaline aminotransferase (ALT), and alkaline phosphatase (ALP) were measured in the seminal plasma. Testosterone and di-hydroxyprogesterone concentration were also measured in the blood serum of samples. AST, ALT and ALP concentration were 48.7 ± 7.29, 16.92 ± 1.57 and 25.4 ± 1.97 U/L respectively. Testosterone and di-hydroxyprogesterone concentrations were 1.23 ± 0.24 and 0.16 ± 0.04 ng/ml. The regression analysis have revealed significant relationship between fish age and sperm volume (R2 = 0.618, P < 0.05), serum triglyceride concentration and sperm density (R2 = 0.347, P < 0.05), serum triglyceride concentration and osmolarity (R2 = 0.471, P < 0.05). There was also observed significant relationship between duration of sperm mobility and ALP concentration (R2 = 0.69, P < 0.01), sperm osmolarity and ALT (R2 = 0.602, P < 0.01) and ALP (R2 = 0.50, P < 0.05) concentrations. In the histological study of testes, spermatozoa were the predominant cells that could be a sign of spermiation stage in the male kutum. The results have shown that transplantation of Caspian Kutum to the Gheshlagh River basian have not adverse effects on male reproductive characteristics.
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