Thymic development in two species of marine teleost; An Antarctic silverfish, Pleuragramma antarcticum Boulenger, and a warmer-water sea bass, Dicentrarchus labrax (LINNAEUS)

摘要

The paired thymic organs of post-larval, juvenile and adult specimens of the Antarctic silverfish, Pleuragramma antarcticwn, and sea bass, Dicentrarchus labrax, were examined histologically. In both species the paired thymic anlagen were infiltrated by small lymphocytes at the earliest post-larval stages. This was more advanced in D. labrax, with the formation of trabeculae from the sub-epithelial connective tissues (SECT). A more advanced thymic development was noted for juvenile D. labrax, trabeculae were prominent and thymic zonation was distinct. In this species there was a greater infiltration of epithelial mucous cells and macrophages into the inner thymic area. A further distinction, not observed in P. antarcticum, was the presence of melano-macrophage centres and large myoid cells, indicating a more advanced thymic involution in the warmer-water species. Thymic progression at the adult stage differed in the two species. D. labrax did not show an increased involution of the thymic zones; however, an increased trabecular and SECT development divided the thymus into discrete lobules. In contrast, the thymic trabeculae were lost in P. antarcticum and the organ regressed, leaving a few aggregations of small lymphocytes in the outer thymic zone.