Effect of Age on Reproductive Indexes in Cultured Rainbow Trout (Oncorhynchus mykiss Walbaum, 1972)

Rainbow trout ) Oncorhynchus mykiss ( is the most important species of rearing cold water fish in Iran. In the propagation process of rainbow trout, different factors involved in quality and quantity of female broods and their eggs and also quality and quantity of male broods and their milts. For these reasons at propagation season in 2008, is studied the effect of different age on reproductive indexes in rainbow trout broods until absorption of yolk sack stage. For this study 3 groups of male and female broods (3, 4 and 5 years old) are selected at random and after anesthetize, their age are determined and are assessed their total length, before and after stripping weight, egg diagonal, total weight of female eggs and sperm quality individually .Then broods are crossed together. The results in 9 treatments showed that in the studied treatments were statistics significant difference in mean of fertilization percentage, survival percentage to eyeing stage and hatching percentage ( p<0.05 ) and the produced eggs from crossing of 5 years old females with 4 years old male have maximum rate in fertilized eggs(98%), hatching(96%), survival rate until absorption of yolk sack stage (94.5%) and number of larva with active feeding(3070). Concerning result of present study and previous studies, the age of broods, affect on fertilization stages. Therefore using of 5 years old females with 4 years old male, improve these stages.