Visual Sensitivity of Lean Lake Trout (Salvelinus namaycush) and Siscowet Lake Trout (Salvelinus namaycush siscowet): A Morphotype Comparison

The Lean Lake Trout (Salvelinus namaycush) is an apex predator within the littoral zone of Lake Superior. These fish exhibit diel bank migration in contrast to the pelagic Siscowet Lake Trout (Salvelinus namaycush siscowet) which perform diel vertical migration. Diel migration is triggered by light levels and temperature which allows for an increase in foraging opportunities. The amount of light that Leans can perceive depends on the amount available at the surface, the depth light can penetrate through the water column, and the visual sensitivity of their photoreceptors. The determination of Leans spectral sensitivity was conducted via electroretinography. The spectral sensitivity of Leans was compared to the pelagic Siscowet which were obtained from Harrington et al. (2015). The peak spectral sensitivity for Leans was 550nm while Siscowets had a peak of 525nm. Both peaks are correlated to the down-welling within Lake Superior. The results supported the Sensitivity Hypothesis which states that a fish’s spectral sensitivity will match the light available in its environment. Leans spectral sensitivity was found to be green-shifted compared to the blue-shifted Siscowet which could be explained by Leans shallower position in the water column. Surprisingly, both morphotypes had similar absolute visual sensitivity despite different photic habitats.