The optimum dose of ultraviolet (UV) irradiation to produce gynogenetic Caspian salmon, Salmo trutta caspius, with emphasis on the "Hertwig effect" and photoreactivation (PR) were investigated. The sperm of Caspian salmon was irradiated with UV at 2010 ? 200 ?w.cm-2 in different times including 0, 1, 3, 5, 8, 10, 15, 20, 25, 35 and 45 min and was allowed to fertilize normal ova; the fertilizati...