When considering the intensive culture of marine fish species and the relationships between aquafeeds and the environment, a major factor influencing the pattern of effluent discharge to the environment is the culture system employed. This paper presents the results of a one-year study on the retention and discharge of nitrogen (N) and phosphorus (P) from a pilot cage farm for on-growing gilthead seabream (Sparus aurata) located in the Canary Islands (Melenara bay, Gran Canaria). Throughout this period, data on fish weight, and body and feed N and P content were collected every three months. In addition, sediments from different areas beneath the cages were also analysed for N and P content at two monthly intervals. The results obtained concerning percentages of N and P retention during the study were similar to those reported by commercial feeds manufacturers for the same species when calculated for similar extruded diets and culture systems. Moreover, analyses of nutrients within the sediments below the cages over the course of the study revealed no noticeable accumulation of solid particulate wastes from the farm.