Co-variation in the genetic architecture, and co-localization of quantitative trait loci (QTL), for embryonic developmental rate and age at maturation in male rainbow trout (Oncorhynchus mykiss) was examined. Two lots (September and December spawning) of 2 x 5 (male x female) diallel crosses were performed and the resulting progeny were raised to maturity. Higher incidences of precocious maturation were observed in the September lot fish compared to December lot fish, which was uncoupled to developmental rate. However, precocious maturation and body size was higher in early hatching December lot fish. A genome scan was also completed across 4 linkage groups previously reported to possess embryonic developmental rate QTL and/or age at maturation QTL. No evidence of co-localization of QTL for the two traits was detected. However, the presence of QTL for embryonic developmental rate on RT-8 and RT-24 and one for age at maturation on RT-17 supports previous results.