Enteroendocrine APUD cells in the digestive tract of larval Barbus conchonius (Teleostei, Cyprinidae).

The development of Barbus conchonius is described with special attention to the differentiation of the gut. Amine precursor uptake and decarboxylation (APUD) are present in enteroendocrine cells during development, whereas these processes are lacking in adult specimens. The first APUD cells originate on the fourth day of development in the anterior part of the gut and on the fifth day in the caudal areas. The APUD facility of the cells disappears within 2 days, and after the 6th day APUD cells can no longer be distinguished in the intestinal epithelium. The first APUD cells were obsserved when four types of enteroendocrine cells were recognized with the electron microscope. These enteroendocrine cells contain granules of different electron densities, and microtubules and cilia can be observed. Some enteroendocrine-like cells are found below the basement membrane of the intestinal epithelium, indicating a possible extra-endodermal origin. APUD cells, except melanoblasts, have not been found migrating from the neural crest in ventral direction. The origin of the enteroendocrine cells of B. conchonius is discussed.