Interspecific hybridization is common in water fleas of the Daphnia galeata species complex (e.g. D. galeata, D. cucullata, D. hyalina and their interspecific hybrids). We studied the effect of fish kairomones on the life-histories of 5 taxa of this species complex originating from the Plußsee, northern Germany. Using four clones per taxon, we found that fish factor reduces size at birth and size at maturity significantly. For size at maturity larger taxa showed a significantly stronger reaction to fish kairomones than the smaller taxa. With respect to the intrinsic rate of increase, r, we compared two predation regimes (positive size selective and not selective). We found that under the fish predation regime most clones had a higher r when cultured with fish kairomones, leading to a higher r, and a stronger reaction for the smaller taxa. We conclude that fish predation might be an important factor influencing the co-occurrence of Daphnia parental taxa with their hybrids.