The effect of diet on larval growth, anionic trypsinogen gene expression (ssetryp1), and trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) activities was assessed in Solea senegalensis. Changes in larval carbon stable isotope (δ(13)C) composition were used to estimate carbon assimilation. Diets were supplied for 20days to fish held in larval rearing tanks and consisted of live rotifers, Artemia sp. nauplii, rotifers followed by Artemia sp., rotifers co-fed with inert diet and inert diet alone. Growth was significantly faster in larvae fed only Artemia and those fed rotifers and Artemia (k=0.381-0.387day(-1)). Trypsin and chymotrypsin activities increased from 3 to 4days after hatching (DAH) in all dietary treatments, while ssetryp1 transcripts increased at 4-5 DAH only in larvae fed live prey. ssetryp1 gene expression was activated later in larvae fed only Artemia and this corresponded with Artemia δ(13)C values being reflected in larval tissue. Larval δ(13)C values also indicated greater selection and/or assimilation of rotifers in relation to the inert diet. Results demonstrate that during early larval development of sole, diet modulates ssetryp1 gene expression. The rapid and intense response to diets that promoted different growth and survival suggests the suitability of this biomarker as a nutritional status indicator in early sole larvae.