Application of DNA parentage assignment for commercial selection in aquaculture is still rare. An experiment was performed to quantify and to minimize maternal effects on growth in rainbow trout. Six hundred families were reared until 198 day post fertilization (dpf) according to two different procedures. In the first procedure (NORM), all families were pooled at eyed stage. In the second procedure (MIN), where maternal effects due to differences in egg size were expected to be minimal, the spawns were divided into sub-groups with similar mean egg weight at eyed stage. These sub-groups were then pooled when they achieved the same mean body length (147 dpf). Genetic parameters were estimated for body weight, body length and condition factor at 198 dpf, with 2964 fish assigned to their parents using microsatellites. Significant maternal effects were observed in the NORM group for body weight and body length (m(2) = 0.08 +/- 0.03). The heritability of body weight was 0.16 +/- 0.07 in the NORM group and 0.36 +/- 0.06 in the MIN group, in which maternal effects were not significant It is concluded that, when eggs of different females are mixed at eyed stage, maternal effects persist at least until 198 dpf. The proposed procedure efficiently limits maternal effects, substantially increasing the heritability for growth, and therefore the expected selection response. (C) 2012 Elsevier B.V. All rights reserved.