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Life history traits of Daphnia galeata clones were affected differently by kairomones exuded by two species of fish. The exposure to Gasterosteus kairomone resulted in an increase in population intrinsic rate of increase and body growth rate relative to the exposure to Perca kairomone. These differences between fish treatments have not been reported earlier. The results suggest differences between fish kairomones that are not due to concentration effects alone. This raises the possibility that kairomones are cocktails of chemicals rather than a single `fish substance'. It also supports the view the effects of size-selective predation vary depending on the local predator–prey assemblage examined. This finding leads to an additional, previously underestimated but potentially complex aspect in zooplankton ecology. [ABSTRACT FROM AUTHOR]