Light conditions influence animal health, growth, product quality, and ultimately the productivity of aquaculture systems. Understanding light requirements of important commercial species is essential, particularly for species such as starry flounder, Platichthys stellatus, held exclusively in land-based aquaculture systems, where building and tank conditions interfere with natural light. In the current study the effects of light intensity – Low (15 lx), Medium (500 lx) and High (2500 lx) on starry flounder in RAS were investigated in two experiments. First, in a 63 days trial, the influence of light on growth performance was determined. In a second trial (33 days), the light induced reaction on blood plasma glucose- and cortisol level was investigated. Juvenile P. stellatus (104.9 ± 0.2 g) held at low ambient light intensities significantly gained weight (44.0 ± 2.6 g) compared to those held at high light intensities (32.4 ± 4.4 g). Lower growth performance at high light intensities was related to a significant decrease of daily feed intake and specific growth rate, even when feed conversion rate and condition factor did not differed among treatments. In the second experiment, individuals with a mean weight of 140.2 ± 1.0 g showed no differences in diurnal plasma cortisol responses, while the plasma glucose levels significantly increased under low light intensities. The present study indicates that improper high light intensity markedly reduces the growth of juvenile starry flounder in land-based recirculating aquaculture systems without causing significant stress responses in terms of plasma cortisol concentrations. Yet, the increased plasma glucose level found under low light intensities could not be related to the observed cortisol levels. Considering growth performance, economic constraints and pertinent animal welfare, adjustment of light conditions to maintain appropriate intensities below 500 lx is recommended for this species in artificial rearing units.