Carotenoid and pterin pigment localization in fish chromatophores

The classical sulfuric acid method for the histochemical detection of carotenoids has been adapted to give a reliable cytological localization of these compounds in fish chromatophores. This procedure consists mainly in fixing skin fragments in glutaraldehyde and dehydrating in a 50% solution of glycerin followed by exposure to air. It is essential that the preparation permit direct contact of the sulfuric acid with the pigment cells. Under these conditions, carotenoid containing cells stain green or blue. When associated with the extraction of the carotenoids by acetone, the procedure permits the distinction between pterin and carotenoid in fish chromatophores.