ONTOGENY OF THE SEA BASS SPLEEN (DICENTRARCHUS-LABRAX) - A LIGHT AND ELECTRON-MICROSCOPIC STUDY

The splenic rudiment in sea bass (Dicentrarchus labrax) appears 18 day s after hatching in the right side of the body, close to the dorsal wa ll of the anterior part of the intestine. It acquires its final locali zation after about 2 months in a middle-ventral position between the c ecal part of the stomach and the first intestinal loop. The haemopoiet ic activity of this spleen during organogenesis varies with age. Durin g the first 40 days only erythropoietic activity is shown, after which thrombopoiesis begins and the first lymphocytes appear. At the time t hat the amorphous extracellular matrix increases, some reticular cells of the stroma undergo an active lipid synthesis, which ceases when th e larvae are about 2 months old. All the above coincides with a decrea se in erythropoiesis and total vascular development, although the elli psoids and sinusoids do not present their final structure until later stages. These structural variations create microenvironmental conditio ns which favor modifications in the activity of the spleen. This relat ion between microenvironment and changes in haematopoietic organ funct ion has also been described in mammals and birds (Metcalf and Moore [1 971] Frontiers of Biology, Amsterdam: North Holland; Quesada et al. [1 985] J. Submicrosc. Cytol. 17:537-540; Yassine et al. [1989] Cell Diff . Dev. 27:29-45). (C) 1994 Wiley-Liss, Inc.