MIGRATING DAPHNIA HAVE A MEMORY FOR FISH KAIROMONES

Kairomones from juvenile perch (Perca fluviatilis) enhance phototactic descent of Daphnia to the hypolimnion of lakes following upon light i ntensity increases at dawn. Kairomones are not present, in the hypolim nion and ascent in the evening might be insufficient for the animals t o reach the epilimnion again. The hypothesis that sensitization is mai ntained for some time in the absence of fish exudates was tested. Expe riments showed that sensitization was indeed maintained for 5-6 days. Thus a kind of ''memory'' for fish kairomones exists, resulting in an enhanced ascent from a fishless hypolimnion at sunset.