Changes of gonadosomatic index and plasma levels of cortisol in the male and female captive Caspian brown trout, Salmo Trutta Caspius (Kessler, 1877) during the reproductive cycle

Abstract

The changes of cortisol and gonadosomatic index (GSI) in male and female Caspian brown trout reared under confinement in the hatchery were determined by radioimmunoassay. When the GSI reached to its maxima (for males: 17.2±1.9 ng/mL; for females: 15.6±4.7 ng/mL), the concentration of cortisol showed a clear peak both in males (10.6±0.8%) and females (10.1±0.9%). This result suggests that the elevated plasma levels of cortisol may not just be due to stresses during the breeding season but also due to its physiological functions in the reproduction of Caspian brown trout.