Cold resistance in the eggs of the capelin Mallotus villosus

Abstract

Eggs of the capelin, Mallotus villosus, are laid superficially on sandy beaches where they may be exposed to temperatures below –5 °C during tidal emersion. The eggs do not freeze until the temperature of their surroundings falls to a mean of –11.9 °C for eggs at the late blastula stage and –10.6 °C for eggs about to hatch, even though films of sea water covering the eggs are frozen. Newly hatched capelin larvae freeze at a mean temperature of –2.5 °C when the sea water surrounding them freezes, and are probably supercooled at temperatures below this before hatching. Evidence is presented which demonstrates that capelin eggs survive low temperatures by supercooling, and that they can do so in the presence of external ice crystals because the chorion prevents ice penetration and hence seeding of the eggs' internal fluids. The chorion of Mallows is shown to possess an extra secondary layer, like that of the related smelts. The primary function of this outer layer appears to be be concerned with adhesion to sand grains but it seems likely that it also prevents or delays ice penetration.