Background illumination conditions, and absorbance spectra and quantum catch of cone pigments in rainbow trout.

<p>(A) Two background illumination conditions were used, a broad-spectrum ‘Natural’ background and a long wavelength (LW) adaptation background. The broad-spectrum background simulated the fish natural photic environment by reproducing the sideward irradiance measured at a depth of 3 m at Lake Cowichan, Vancouver Island, BC, Canada (root mean square error = 0.38 log photons cm⁻² s⁻¹; Pearson <i>r</i> = 0.94). The LW adaptation background was designed to dampen the sensitivity of the LWS cone mechanism. (B) Absorbance spectra of the cone pigment classes in rainbow trout. Based on the range of photoreceptor sensitivity, absorbance spectra were constructed while assuming visual pigments are of A1 chromophore. (C) The number of photons collected by the various cone pigment classes under the background conditions used, as estimated using a quantum catch model. (D) The ratio between the quantum catch (QC) of pigments under the LW adaptation and Natural backgrounds was highest for LWS, indicating that LWS is the pigment being adapted most extensively under the LW adaptation compared to the Natural background.