Effect of age on reproductive efficiency of adult rainbow trout, Oncorhynchus mykiss Walbaum, 1972

Rainbow trout, Oncorhynchus mykiss is one of the most important cold water fishes in Iran. For successful artificial propagation of rainbow trout, the quality and quantity of brooders and sexual materials are key factors. In the present study, we investigated the age-dependent changes of reproductive efficiency. For this purpose, the brooders were divided into age classes and then three age groups of male and female (i.e. 3, 4 and 5 years old) selected randomly from each age class. At the time of propagation, total length and weight of brooders before and after stripping, egg diameter, total weight of stripped eggs and sperm quality parameters including sperm density and spermatocrit were measured. Afterward, the brooders were crossed randomly. According to our results, the higher percentage of fertilization (98%), hatching (96%), survival (94.5%) and also the larvae with more active feeding (n= 3070) were found when the 4 year old males were crossed with 5 year old females (p