PREDATOR-INDUCED DIEL VERTICAL MIGRATION IN DAPHNIA - ENRICHMENT AND PRELIMINARY CHEMICAL CHARACTERIZATION OF A KAIROMONE EXUDED BY FISH

Planktivorous fish release a cue of an unknown chemical nature into th e water that induces diel vertical migration in Daphnia as predator av oidance response. We used a bioassay to obtain information about the c hemical nature of the kairomone. We present a method to enrich the cue from holding water of fish by sorbent extraction. The kairomone exude d by Leucaspius delineatus can be characterized as a nonolefinic low-m olecular-weight anion of intermediate lipophilicity. The presence of a mino groups in the molecule can be excluded, whereas hydroxy groups ar e essential for activity. Separation by HPLC yielded only one active f raction. The kairomones released by Carassius carassius and Rutilus ru tilus showed the same chemical characteristics, suggesting that the ka iromones from different species of fish, sensed by Daphia, are very si milar, if not identical.