Patterns of pigmentation in the eye lens of the deep-sea hatchetfish,Argyropelecus affinis Garman

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Abstract
The present study is a morphological, biochemical and spectrophotometric characterization of the eye lens pigmentation in 45 specimens (11–88 mm in standard length) of the deep-sea hatchetfish,Argyropelecus affinis (Stomiiformes: Sternoptychidae). For comparison, we also examined available lenses of other members of the family Sternoptychidae, including three other species of the genusArgyropelecus, and two species of the genusSternoptyx. Lens pigmentation was observed in all specimens ofArgyropelecus spp. larger than about 36 mm in standard length, but was absent in allArgyropelecus spp. individuals less than 36 mm. However, lens pigmentation was not observed inSternoptyx specimens of any size. Detailed studies ofA. affinis indicated that (1) at 36 mm the nascent lens fiber cells, which are continually laid down over preexisting, unpigmented cells, begin incorporating pigment, and (2) the pigment concentration increases steadily as pigmented cells are added during lens growth. Spectrophotometric and biochemical data suggested that the pigment is a carotenoprotein complex, the carotenoid-like chromophore being strongly associated with a specific soluble lens protein, alpha crystallin. While the lens coloration in these fishes is age-related, analyses of the retinal visual pigment revealed no concomitant age-related change in the peak wavelength of retinal sensitivity in these fishes. Our data on the spectral absorbance of the lens and visual pigment of these fishes suggest that the lens pigmentation acts as a short-wave filter to improve acuity of the visual system.