Reveco, F. E. and Drew, M. D. 2012. Fractionation of wheat distillers' grains and solubles by particle size and density improves its digestible nutrient content in rainbow trout. Can. J. Anim. Sci. 92: 197-205. The nutritional value of wheat distillers' dried grains and solubles (WDDGS) in aquaculture is poor because of its relatively low crude protein (CP) and high fibre content. In this study WDDGS was fractionated using grinding, sieving and elutriation sequentially. The WDDGS was ground in a hammer mill using a 3-mm screen and sieved using six sieves (20M, 30T, 40T, 50T, 60M and 80M) into seven fractions (>841, 590-840, 426-589, 298-425, 251-297, 178-250 and<177 µm). Elutriation was then performed to further fractionate based on particle shape and density. The higher density sub-fractions from the three smallest particle size fractions were mixed to produce a fractionated WDDGS containing 20.7 MJ kg^-1 gross energy (GE), 454.6 g kg^-1 CP, 260.4 g kg^-1 neutral detergent fibre (NDF) and 93.2 g kg^-1 acid detergent fibre (ADF). The digestibility of the unprocessed and fractionated WWDGS products was assessed in rainbow trout. Apparent digestibility coefficient (ADC) of DM, GE, acid ether extract (AEE), ash and amino acids (AA) did not differ between the unprocessed material and the fractionated WDDGS (P>0.05). However, the ADC of CP was higher for fractionated WDDGS (0.88) than the unprocessed WDDGS (0.85) (P<0.05). This fractionation scheme can be used to improve the nutritional value of WDDGS for rainbow trout.