Spectral absorbance changes in the photoreceptors of the juvenile masked greenling, Hexagrammos octogrammus (Pisces, Hexagrammidae).

Abstract

When changing habitat during migration or ontogenesis, fish encounter changes of the visual environment, among which the most important is the spectral composition of light and turbidity. This leads to changes in the behavior, morphology, and physiology of the visual system, in particular, spectral sensitivity, which is determined by the properties of visual pigments. The masked greenling Hexagrammos octogrammus has an additional factor that shapes effective spectral sensitivity-the presence of densely bright orange cornea which reversibly changes its density depending on the state of light/dark adaptation. However, it is unknown to what extent the properties of visual pigments are matched to spectral properties of the developing cornea at the final stage of metamorphosis during migration of juveniles from pelagic to coastal environments. The findings of this microspectrophotometric study show that the range of the spectral sensitivity of rods and cones in juveniles is much wider than in adults, with a shift in the sensitivity of a significant part of the cells to shorter wavelengths. The reason for this is the large variation in the ratio of chromophores A1:A2 in the pigment mixture in each cell and possible expression of new opsins. This also indicates the asynchrony of pigment transformations in different types of photoreceptors and the incompleteness of these transformations on the eve of the transition to bottom life in shallow water.