Apoptosis of thymocytes in developing sea bassDicentrarchus labrax(L.)

This study showed occurrence of an apoptotic process throughout the thymic development of a teleost fish. The thymus of larvae and juveniles ofDicentrarchus labrax(L.) was processed forin situend-labelling of fragmented DNA. Apoptotic cells were not found in the thymic anlage, and were first detected at day 35 post-hatching. Their number did not change significantly throughout early thymic development, while it increased at day 74 post-hatching. Apoptotic thymocytes were more frequent in the cortex than in the medulla, and notably concentrated between the two regions. Apoptotic cells were less numerous in juvenile specimens, without changing the pattern of distribution. The apoptotic process has been confirmed by analysis for both high- and low-molecular weight DNA fragments and by cytomorphology.