The effects of salinity and low temperature on eggs of the Icelandic capelin Mallotus villosus

Abstract

The embryos of Icelandic capelin (which spawn subtidally) tolerate as low temperatures, and are as euryhaline, as those of Balsfjord capelin which spawn intertidally. The median lethal lower temperature for Icelandic capelin eggs exposed for 6 h to low temperatures in frozen seawater films (34‰) is -6.3°C. The median lethal high salinity (6 h exposure) is 88.3‰. Eggs were reared and hatched successfully in all salinities from 1.5 to 34‰. When exposed to high salinities capelin eggs shrink in a matter of seconds (shrinkage being manifested in depressions of the chorion), but resume a normal shape in a few minutes as salts diffuse into the perivitelline fluid. Evidence is presented to show that mortality in frozen seawater films is due to osmotic dehydration, rather than to a final invasion by ice crystals. A model of freezing avoidance in capelin eggs is described.