SUMMARY
Microspectrophotometry was used to measure the visual pigments in the rods and cones of 22 species of marine fish larvae netted from the surface waters off Friday Harbor Laboratories, Washington, USA. 13 species had rods, 12 of which contained visual pigments with a wavelength of maximum absorbance near 500nm, while one, the sand lance (Ammodytes hexapterus), had its absorbance maximum at 482nm. The 22 species of fish larvae possessed varied combinations of single, double and twin cones, ranging in peak absorbance from 353nm to 584nm. Of these, green-sensitive single cones were present in 20 of the 22 species, and were the dominant cone type. Double and twin cones were present in 13 of the species. Most common were identical green-sensitive (twin) cones (in 11 species). Green/yellow-sensitive double cones occurred in four species. In a single instance (Hemilepidotus hemilepidotus) twin blue-sensitive, twin green-sensitive and double blue/yellow-sensitive cones were recorded. Of particular interest was the finding that 18 of the species had ultraviolet- and/or violet-absorbing single cones.
It has been suggested that short-wavelength photosensitivity may be beneficial for planktivory by extending the spectral range over which vision can occur. The high percentage (82%) of ultraviolet and violet visual pigments in Pacific northwest fish larvae supports the prediction that short-wavelength sensitivity may be common in marine fish larvae.
