Visual pigments of Arctic charr (Salvelinus alpinus (L.)) and whitefish (Coregonus lavaretus (L.)) morphs in subarctic lakes

Foraging trait specialization is important for polymorphic Arctic charr and whitefish, but visual capabilities of different morphs are unexplored. Photoreceptor complements and absorbance spectra of rod visual pigments were studied by microspectrophotometry in two sympatric Arctic charr morphs and three sympatric whitefish morphs from two subarctic lakes. Four spectral classes of photoreceptor cells, rods and three types of cones, were found in all morphs of both species. Arctic charr rods had a pure A1 pigment (rhodopsin) with wavelength of maximum absorbance λmax ≈ 511–512 nm and no significant differences either between littoral and profundal morphs or sampling times (January/August). Rods of littoral and pelagic whitefish had practically pure A2 pigment (porphyropsin), whereas profundal whitefish had chromophore mixtures with A2:A1 ≈ 0.8:0.2 in June, A1 decreasing to a smaller fraction in September. λmax values of littoral and pelagic whitefish rods were similar and did not change significantly with season (539.3 ± 0.3 nm/539.3 ± 1.1 nm and 538.4 ± 0.4/539.8 ± 0.3 nm in June/September) but differed from profundal whitefish (λmax = 531.5 ± 0.8/536.7 ± 1.0 nm). Differences between Arctic charr and whitefish morphs suggest importance of local light environment determining visual pigment composition.