ABSTRACT
Microspectrophotometry of single retinal photoreceptors of larval California topsmelt, Atherinops affinis, and the grunion, Leuresthes tenuis, revealed the presence of a cone cell that contained an ultraviolet visual pigment (maximum absorbance at 355 nm, half bandwidth 70 nm). Topsmelt larvae 6–19 mm standard length fed on Artemia when exposed to ultraviolet (UV–A, 300–400 nm) light alone at least as well as in full sunlight. Grunion 24 hours after hatching 6–8 mm standard length also fed on Artemia in UV–A light alone. Measurement of the spectral near-surface radiance field in which both species forage indicate that UV–A photons between 300 and 400 nm constitute as much as 18–20 percent of the total number of photons between 300 and 750 nm. The data imply that ultraviolet vision in these obligate planktivorous larvae facilitated foraging. We suggest that the ability to detect zooplankton in the near-ultraviolet may be widespread amongst fish larvae that forage on zooplankton where ultraviolet light intensities are high.
