Rapeseed was grown originally for supplying steam engine lubricant, but it is nowadays an oil source in human and animal diet. Rapeseed/canola seeds are initially processed into two components: oil and meals. Despite the improvement of the quality of the rapeseed/canola products that can be obtained by a variety of selected technological treatments, there are limitations to their use in animal diets, including fish diets. Meal quality is influenced by several variables during the process, especially temperature, and there are other operations that can be performed, such as the dehulling of the seed before the oil extraction. Rapeseed/canola protein concentrates and upgraded meals are expected to have improved nutritive value for finfish. The protein isolates are more expensive than protein concentrates because of their higher quality and their higher biological value. Since the 1990s, extrusion treatment has been applied to improve the quality of some legume seeds, such as soybeans or rapeseed.