Effects of Salinity and Temperature on Embryonic Development of the Pacific Cod (Gadus macrocephalus)

Eggs of the Pacific cod (Gadus macrocephalus Tilesius) were held from fertilization to completion of hatching in various combinations of constant salinity (19–31‰) and temperature (2–10 C). Hatching occurred in all salinities and temperatures, and survival was highest at the lower levels of both factors. A direct and approximately linear relationship was found between rate of development and temperature within the temperature range employed. At each temperature the length of the incubation period was increased at lower salinities. It is suspected that eggs were subjected to hypoxial conditions in the experiments, a circumstance considered to have depressed survival rate over all experimental combinations. There was, in general, an inverse relationship between salinity and temperature with respect to both size of larvae produced and the duration of the hatching period. Calculated response isopleths suggest that eggs of Gadus macrocephalus are euryhaline, and that maximum hatching success may be found in the vicinity of 19‰ S and 5 C. Changes of 1 C were calculated to be equivalent in effect on hatching success to a change of about 12‰ S.