Interspecific hybridization is common in water fleas of the Daphnia galeata
species complex (e.g. D. galeata, D. cucullata, D. hyalina and their inter
specific hybrids). We studied the effect of fish on the life histories of l
ive taxa of this species complex originating from the Plusssee, northern Ge
rmany. Using four clones per taxon, we found that fish kairomones reduce si
ze 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 compare
d two predation regimes (positive size selective and not selective). We fou
nd that under the fish predation regime most clones had a higher r when cul
tured 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 h
ybrids.