Fig. 10. Micrographs of sections from smolt and adult retinas following double label in situ hybridization with the green (rtGR) and red (rtRE) riboprobes or with the UV (rtUV) and blue (rtBL) riboprobes. (A) Tangential section from the centro-temporal retina of the smolt showing that each member of a double cone expresses a mRNA encoding green opsin (blue colour) or red opsin (red colour), and that these alternate around the unit mosaic. (B) Tangential section from the centro-dorsal retina of the smolt, adjacent to the embryonic fissure, shows two faint UV riboprobe labels (though no associated cone morphology is clearly discernable) among the single cone population. (C,D) Tangential sections from the centro-dorsal (C) and centro-temporal (D) retina of adult rainbow trout showing the same labelling pattern of double cones as in the smolt retina. Symbols and nomenclature as in Fig. 5. Magnification bar (in A) is 25 µm and relates to all panels.