Early presence of immune cells in the developing gonad of the gilthead seabream (Sparus aurata Linnaeus, 1758).

A great deal is known regarding the process of sex differentiation in fish. However, little is known about the presence of immune cells and cytokines in this process. In the gilthead seabream, both immune cells and cytokines play an important role in the tissue reorganization of the gonads during the adult reproductive cycle. We have studied, using light microscopy and immunocytochemistry, the ontogenetic development of the gilthead seabream gonads, focusing on the presence of immune cells and cytokines. We show that the testicular area is quickly differentiated and becomes functional in specimens less than a year old, while the ovarian area differentiates later and continues to develop during the first two years of life. Throughout the morphogenesis process, acidophilic granulocytes were present in the gonad. Interleukin-1b (Il1b) is produced in the testicular area in juveniles and male fish, but not in the ovarian area. Macrophage-colony stimulating factor receptor (Mcsfr) is not produced in the undifferentiated gonad and is only found once the testicular area is well developed.