We investigated the effect of timing of food intake on growth in common carp (Cyprinus carpio L.). Juvenile carp were demand-fed for 22days using a computerized pendulum feeder that registered meal requests. Controls were pair-fed at 10:00h, both groups were kept at 12L:12D (lights on at 06:30h). Demand-fed fish displayed highest food intake at 22:00h, and the lowest at 10:00. After 22days, demand-fed fish had grown by 20% of their initial body weight, compared to 4% of the pair-fed control. Plasma cortisol levels in demand-fed fish were remarkably low and stable, whereas in the control group levels had increased 60-fold at 10:00h compared to 22:00h. Hepatic mRNA expression of leptin-a1 and leptin-a2 also differed markedly between groups and time points, with leptin-a2 expression being lowest in the demand-fed group at the time point of lowest food intake. We conclude that timing of food intake is an important determinant of endocrine status, growth and welfare.