The stress responses in early growth stages of the wedge sole have been studied to determine whether the high cortisol levels described in juvenile fish are present from early developmental stages. Whole-body cortisol, glucose and lactate contents, as well as biometric parameters in wedge sole larvae were measured at three different stocking densities. Stocking density affected growth-related variables significantly, and larvae in lower stocking densities grew faster. Survival did not significantly differ among treatments. At hatching, the whole-body cortisol concentration was 0.33 ± 0.01 ng g−1 and varied significantly from 0 to 30 days after hatching ( DAH) for each stocking density, though values remained stable for the remaining time in the low-stocking density group. These hormone levels rose significantly (5.17 ± 2.43 to 22.10 ± 4.95 ng g−1) at the end of the experiment, depending directly on the stocking density. Glucose and lactate-body concentrations did not vary among treatments. We conclude that the stress responses of wedge sole larvae are detectable from 45 DAH and that stocking density already can be a stressor at that age. As described for juvenile stage, cortisol content values in wedge sole larvae under non-stressful conditions are one of the highest among those reported in the literature. The captivity conditions could be responsible for this apparently stressful situation, though those values also could be normal in wild specimens. [ABSTRACT FROM AUTHOR]