To improve the quality of reproduction in Eurasian perch, Perca fluviatilis L., which is a promising candidate for Eurasian freshwater aquaculture that is currently cultivated in recirculating aquaculture systems (RAS), investigating the hormones that mediate and affect reproduction in this species is indispensable. The literature defines a group of four major corticosteroids (11-deoxycorticosterone, 11-deoxycortisol, corticosterone and cortisol) that might mediate critical stages of reproduction in female perch. Unfortunately, neither the basic roles nor the kinetics of these four corticosteroids throughout the reproductive cycle of female perch have been well defined to date. In this study, we therefore elucidated the plasma kinetics of these four corticosteroids during the reproductive cycle of domesticated female perch while monitoring the expression of the different receptors and enzymes that mediate their pro-duction and possible functions. Additionally, we performed an in vitro experiment during late vitello-genesis to investigate the possible direct roles of these steroids during that stage. Our results revealed that these four corticosteroids were detectable throughout the reproductive cycle, and the levels of most of them (11-deoxycorticosterone, 11-deoxycortisol, and cortisol) fluctuated significantly depending on the stage of reproduction. 11-Deoxycorticosterone and 11-deoxycortisol exhibited their highest levels, 1.8 ng/ml and 58 ng/ml, respectively, at the beginning of the reproductive cycle. By the end of the reproductive cycle, 11-deoxycortisol and cortisol plasma levels exhibited a surge, reaching 58 ng/ml and 150 ng/ml, respectively. During the perch reproductive cycle, the corticosteroid receptor complex is not regulated only at the hormone level, as the expression levels of all corticosteroid receptor genes showed a progressive and similar decline. In vitro exposure of vitellogenic oocytes to some of these corticoste-roids (11-deoxycorticosterone and 11-deoxycortisol) induced an increase in yolk globule diameter and a decrease in the density of yolk globules, which indicates the involvement of both of these hormones in yolk globule coalescence. Taken together, these results implicate corticosteroids in the reproductive cycle, although the related cellular mechanisms remain to be investigated.(c) 2023 Elsevier Inc. All rights reserved.