Most of the studies aimed at increasing the growth rate of the eels using hormone treatments were on juvenile eels. In this study, European eels with an average weight of 3.1 :t 1.1 g were stocked in a superintensive recirculating aquaculture system in 3 treatment groups, i. e. groups of high stocking density (22.5 kg / m2) with or without estradiol-17 β (60 mg / kg feed) and a low density (7.5 kg / m2) group.