Principal cell types in the pancreatic islet of a teleost fish, Xiphorphorus helleri H

By means of correlative light and electron microscopy, five pancreatic islet cell categories are described in the teleost fish, Xiphophorus helleri, each of which has specific light microscopic appearance and fine structure. Different histochemical techniques have been used, including immunofluorescence with antiporcine insulin and glucagon sera. In addition to B- and A1-cells, two categories of A2-cells have been observed both reacting with antiporcine glucagon serum: A2-cells with round granules gave a positive reaction for tryptophan; have been observed, both reacting with antiporcine glucagon serum: A2-cells with crystalline granules gave a negative reaction with the same staining technique on the same section. The "clear cells", the last category, were not specifically stained by any of the staining methods carried out in this investigation. The influence of fixation on staining affinities and on ultrastructure was shown to be considerable.