Successful methods have been developed for the artificial fertilization and rearing of the eggs and larvae of Pacific herring, Clupea pallasii Cuvier. A salinity optimum (11.53‰ to 16.24‰) for development and survival of eggs and larvae was evident in a study of the effects of constant and changing salinity (0‰ to 34.28‰). However, there is a wide salinity tolerance (6.06‰ to 34.28‰) for both eggs and larvae. Eggs transferred to pond water (0‰ salinity) during the first few days of development perish within a few hours, but if transferred at a later stage, they will survive for at least two days. No apparent correlation exists between survival of eggs and magnitude of salinity change. During development, two critical stages are apparent: the first at blastopore closure, the second prior to and during hatching.