EGG MORTALITY AND HATCHING RATE OF BALTIC COD (GADUS-MORHUA) IN DIFFERENT SALINITIES

Egg mortality of Baltic cod (Gadus morhua L.), collected off northern Gotland, Sweden, in 1990, was studied in four different salinities - 10 and 15 ppt (salinity of the principal spawning areas of Baltic cod) and 5 and 7 ppt (salinity above the halocline) - in laboratory experiments. Mortality was high during the first 4 d of development, but after gastrulation mortality was low in all salinities tested, except for 5 ppt, in which mortality increased slightly before hatching. Mortality during hatching varied considerably with salinity. No hatching occurred in 5 ppt salinity, and only a few larvae survived in 7 ppt salinity; in contrast, mortality during hatching was comparatively low in salinities of 10 and 15 ppt.