Ontogeny of immune organs during early developmental stages of turbot
大菱鲆早期发育过程中免疫器官的发生

A histological study was performed to investigate the development of immune organs in turbot Scophthalmus maximus from hatching to 60 days after hatching (DAH). The temporal sequence of the appearance of immune organ anlages was head kidney, spleen, and thymus. At 1 DAH, head kidney anlage and primordial stem cells were observed. Spleen anlage was present at 5 DAH, became lymphoid at 27 DAH, and developed slowly. Progenitor thymus appeared at 13 DAH, and grew quickly. An outer zone and an inner zone in the thymus were observed. Cell migration occurred between thymus and head kidney. The first functional lymphoid organ was thymus, being followed by head kidney and spleen. During the posterior developmental period of the immune organs, the melano-macrophage centers (MMCs) were not found in thymus, but was found in spleen and head kidney, with higher abundance in spleen. During the early developmental stages of turbot larvae, before the maturity of immune organs, non-specific systems might play an important role in the immunocompetence mechanisms.