سعید حاجی رضایی

Reproductive cycle in female and male Caspian brown trout (Salmo trutta caspius) was investigated by sampling blood plasma and gonadal tissue from 4-year-old fish. The reproductive cycles of both female and male Caspian brown trout are characterised by distinct variations in gonadal size and developmental stage and these are associated with changes in sex steroids. In females, ovarian development progressed merely until vitellogenesis stage while male fish completed testicular development and produced milt at January. Milt had good quality in terms of percentage and duration of motility, milt volume and sperm density. In females, the average diameter of the largest follicles increased steadily throughout the course of experiment and was coincident with changes in the concentration of sex steroids. Beginning in September, plasma testosterone (T) elevated from October to November and then remained unchanged until the end of the experiment. With a one month lag than T, the increasing trend of plasma estradiol (E2) was observed in September to October and then E2 levels decreased steadily for the rest of the experimental period. Plasma progesterone (P) levels were low throughout August to November, but sudden increases were observed during December and January. The concentrations of plasma calcium (Ca) increased significantly during October and November but then declined steadily until the end of experiment. In males, Plasma T increased rapidly, culminating in a transient peak in December. This peak was followed by a steady decline afterwards. Such increasing pattern was observed after October for P. Although E2 concentrations were low throughout the experiment, a weak peak was observed in October. The gonadosomatic index increased continuously for both female and male Caspian brown trout during gonadal development. In conclusion, our results showed that unlike 4-year-old female Caspian brown trout, the male fish can complete final maturation under cultural conditions i