The embronic and larval development of the rainbow trout

Photographs of the developing rainbow trout, Salmo gairdneri Richardson, are presented in sequence from the initial cleavage through hatching. Approximately 3,000 eggs were incubated in standard hatchery troughs supplied with spring water at a constant temperature of 54° F. Accepted fish cultural methods were followed to insure normal developmental patterns. Samples of these eggs were taken for study at 1‐hour intervals from the 5th to the 24th hour after fertilization; then once every 6 hours until they were 72 hours old; then at 1‐day intervals through the peak of hatching on the 23rd day. The embryos were fixed in 5 percent neutral formalin containing 0.95 percent sodium chloride, stained in Harrisˈ hematoxylin, and photographed with a vertically mounted camera.