This data set represent the results from a experiment designed to uncover potential rapid life-history evolution in a Daphnia pulex population in response to a shift in predation regime from phantom midge larvae (Chaoborus flavicans) to fish (Perca fluviatilis) after the illegal intoduction of perch to the study site, Lake Myravatn in the western part of Norway. The aim was to disentangle possible genetic change from phenotypic change in life-history traits. D. pulex were collected before and after the introduction of fish, to create seperate linages. 13 pre-introduction (before the perch- introduction) and 14 post-introduction (after the perch-introduction) clones, in total 27 clones, were used in the experiment. For logistic reasons, the experiment was performed in three separate but procedurally identical batches. Juveniles born within 3-hour intervals were kept in 200 ml glass jars until 45 hours old, and then transferred individually into 70 ml glass jars. Animals were maintained in a climate room at 19 °C with a 16:8 light:dark regime throughout the experiment. All animals were photographed daily for lenght-at-age measurements and when approaching time of maturation, the animals were checked every three hours until all were mature. Juveniles were counted for the first three clutches. Egg size was measured from the photographs of females bearing their first clutch.