Brood stock rainbow trout (Salmo gairdneri) were fed diets low, intermediate, and high in energy and protein over a 3-year period. At the end of the study fish fed diets high in energy and protein weighed more and produced a greater number of larger eggs than did fish fed diets intermediate or low in energy and protein. The average total number of eggs produced by 3-year-old spawners were significantly less than that produced by either 4- or 5-year-old fish; numbers produced by the two older groups of fish did not differ. There was no significant difference in percentage of eyed eggs of 3-, 4-, or 5-year-old fish fed different diets; but the percentage of eggs that reached the eyed stage tended to decrease as age of the fish increased. Number of eggs produced per kilogram of body weight was greatest in 3-year-old fish fed a low-energy, low-protein diet; numbers did not differ between 4- and 5-year-old fish. No significant differences existed in weight of eggs per kilogram of body weight between f...