Knowledge from previous studies directed at locating quantitative trait loci (QTL) for body weight (BW), condition factor (CF) and maturation timing (MT) in rainbow trout was used to investigate these putative QTL associations across 12 linkage groups in a diallel maternal x paternal half-sib family design. Three F1 inter-strain brothers (Spring Valley x Rainbow Springs cross), all descendants of the same granddam known to transmit an extremely high incidence of precocious maturation to her offspring, were crossed with a pure Spring Valley female and a hybrid F, female. Significant (p < 0.05) BW QTL were identified on RT-7, RT-8, RT-9, RT-13, RT-15, RT-17, RT-23, RT-24 and RT-31. Significant CF QTL were identified on RT-8, RT-13, RT-15, RT-19, RT-21, RT-23 and RT-24. Three and two of the five parental fish demonstrated MT QTL on RT-8 and RT-23, respectively, independent of BW QTL indicating that these regions may possess a true and major genetic influence on MT that is largely unconfounded by the fish's body mass growth trajectory. Two separate regions on RT-24 appear to be associated with either BW or MT and may confer a pleiotropic effect on these traits. Three of the five parental fish showed evidence of MT QTL on RT-24, with two of these three QTL effects unrelated to BW. Increased fine mapping of these regions would be beneficial to the understanding of their independent effects.