Fig. 3. (A) A frequency histogram for the _max of all long wavelength cone scans, obtained from both aquarium-reared and wild-caught fish, calculated using the running average (`over-the-top' OTT) <sub>max</sub>, but only presented if bandwidth data was also available from the individual scan. These data were used to calculate the ratio of bandwidth:OTT <sub>max</sub> shown in (B). (B) Plot of OTT <sub>max</sub> versus bandwidth:OTT <sub>max</sub>, calculated for long-wavelength-sensitive visual pigment records, from black bream of different stages of development (diamonds). The lines labelled `A₁-boundary' and `A<sub>2</sub>-boundary' model the bandwidth ratios of pure rhodopsin and porphyropsin pigments, respectively. The lines labelled `P520₁ to P575₁' and `P520<sub>1</sub> to P575<sub>2</sub>' show the modelled bandwidth ratios of visual pigment mixtures formed firstly by two rhodopsins, and secondly by a hypothetical rhodopsin and porphyropsin. The best-fitting, two-peaked, curve (labelled `P520₁ to P550₁ to P575₁') is provided by the model involving the mixture of these rhodopsins in sequentially expressed pairs