Fish lens transmission was found to vary depending on the type and concentration of short-wave absorbing compounds present within the lens. Pigments extracted from lenses of ten species were identified as mycosporine-like amino acids (mainly palythine, palythene and asterina-330, ��maxs around 320-360 nm) which are also thought to be present in the majority of the 120 species examined here. A novel mycosporine-like pigment with ��max 385 nm was isolated from the lens of the flying fish, Exocoetus obtusirostris, while lenses of several closely related tropical freshwater species were found to have high concentrations of the tryptophan catabolite 3-hydroxykynurenine (��max 370 nm). The type of lens pigment a species possesses and its concentration depends upon both the animal's phylogenetic group and its "optical niche". �� 1993.