As processing can affect the digestibility and utilisation of diets by fish, we examined the effects of grinding, steam conditioning and extrusion of a commercially available diet (SP35) on weight gain and performance of silver perch. SP35 (35% protein, 18 MJ/kg gross energy) with approximately 80% of particles between 710 and 1000 μm was either left (unground) or finely ground to 500 μm (ground). Both unground and ground fractions were made into sinking pellets in a commercial steam pelleting mill with or without the addition of steam (90 o C) A fifth diet was processed by pelleting finely ground material in a single-screw extruder (after the addition of approximately 5% fish oil) at a temperature of 120 o C. The extruded diet floated or sank slowly. Each diet was fed to 50 juvenile silver perch (mean initial weight 17.8 g) in each of three replicate 10 000-l tanks for 113 days. Fish gained between 55 and 71 g/fish during the experiment, and feed conversion ratio (FCR) ranged from 1.5:1 to 2.0:1. Steam conditioning significantly improved weight gain and FCRs while neither grinding nor the interaction between grinding and steam conditioning had any effect. Fish were reluctant to consume the extruded diet and grew less on this diet than on the steam-conditioned diets, although FCR was better than for all other diets. Ground diets, uncooked and steamed, and the extruded diet were subsequently reground and 1% chromic oxide was added as an inert indicator. Each of these three diets was fed to juvenile silver perch (mean initial weight 2.5 g) in 170-l cylindroconical tanks from which faeces were collected by settlement to determine digestibility coefficients for dry matter, energy and nitrogen. Digestibility coefficients for dry matter and energy were higher for the extruded diet but similar for the unsteamed and steamed diets. Protein digestibility was unaffected by processing. These results indicate that for silver perch fed diets similar to SP35, diets should be steam-conditioned, but the additional expense associated with fine grinding is unwarranted with respect to gains in either fish performance or improvements in pellet stability. Extrusion significantly improved digestibility and FCR but consumption of floating extruded pellets was reduced in our facility. Sinking, extruded diets deserve evaluation.