Successful methods have been developed for the artificial fertilization and rearing of the eggs and larvae of Pacific herring, Clzlpen pnllasii Cuvier. X salinity optimum (1 1 . 53°/aa to 16. 2 4°/~~) for development and survival of eggs and larvae was evident in a study of the effects of constant and changing salinity (OO/oo to 34.2S0/0a). Hornever, there is a \vide salinity tolerance (6.06°/00 to 34.281/aa) for both eggs and larvae. Eggs transferred to pond water (OYaa salinity) (luring the first few days of development perish within a few hours, but if transfcrrccl a t a later stage, they \\,ill survive for a t least two days. No apparent correlation exists between survival of eggs and magnitude of salinity change. D~~r i n g development, two critical stages arc apparent: the first a t blastopore closure, the second prior to and during hatching.