Relative cone opsin gene expression for tilapia given as a percentage of the total cone opsin expression as a function of age in days (post-fertilization). The upper panel shows the expression of shorter wavelength sensitive opsins, which occur in single cones (SWS1 ●, SWS2b and SWS2a ◆). The lower panel shows the longer wavelength sensitive opsins, which occur in double cones (RH2b ● RH2aα , RH2aβ ▲ and LWS ◆). This includes 24 separate time points with three to seven individuals sampled at ages <100 days and one or two individuals for ages >100 days. See Additional file 3 for curves fit to data.