The ice nucleation temperatures of different homogenised organs of the
mussel Mytilus edulis L. were examined. The stomach and the hemolymph
had the highest nucleation temperatures. In the homogenised stomach t
he nucleation temperatures were fairly constant throughout the year, w
hereas the nucleation temperatures of the hemolymph increased in the c
old season. Bacterial growth experiments, microfiltration, and experim
ents using antibiotics indicated that the nucleators were not of bacte
rial origin. The nucleation temperatures of natural seawater were appr
oximately -9 degrees C, whereas seawater made from distilled water and
sea salt had nucleation temperatures of about -17 degrees C. The nucl
eation temperatures of the seawater were reduced when the seawater was
filtered by the mussels. However, no clear indication that the nuclea
tors in the stomach were obtained from the seawater was found. Stomach
homogenates from mussels kept in nucleator-free water had the same su
percooling points as stomach homogenates from mussels kept in natural
seawater. This indicates that the nucleators in the stomach are not ob
tained from the seawater. The temperature and light conditions examine
d in the present study did not significantly influence the hemolymph i
ce nucleation temperatures of mussels kept in the laboratory.