Lemon (Citrus limon) is the third most important species of citrus in the world, while Spain is the major producer in Europe. Numerous beneficial effects of lemon are known, which explains their use in traditional medicine. The paper describes the effect of dietary dehydrated lemon peel (a sub-product of the lemon industry) on the growth, immune and antioxidant status of gilthead seabream (Sparus aurata L.) over a period of 30 days. Fish fed diets enriched with dehydrated lemon peel (1.5% and 3%) for 15 days showed improved growth and both humoral (seric immunoglobulin M) and cellular (peroxidase activity and phagocytic ability of head kidney leucocytes) immunity, as well as the expression of some immune-related genes (nkefa, il1β, igth and csfr1). However, decreases growth promotion was observed after thirty days of trial. Neither the anti-oxidant enzymes activity nor the expression of several anti-oxidants and anti-stress genes in liver was improved by the diet. The possible inclusion of dehydrated lemon peel in fish diets for its immunostimulant effects is discussed.