THE CONTRIBUTION OF ULTRAVIOLET AND SHORT-WAVELENGTH SENSITIVE CONE MECHANISMS TO COLOR-VISION IN RAINBOW-TROUT

Color vision in rainbow trout was studied by characterizing the spectr al sensitivity of single units in three areas of visual processing: op tic nerve; optic tectum; and torus semicircularis. Sensitivity to medi um wavelength stimuli was a common feature of all single units examine d. Additionally, long wavelength sensitivity was found in all units th at were not medium wavelength-only or monophasic. Ultraviolet and shor t-wavelength sensitivity was common in small, juvenile trout, with ult raviolet sensitive units found in the optic nerve and torus, and short wavelength sensitivity found in the optic nerve and tectum. The short er wavelength inputs were excitatory and, if found in the same unit, s ynergistic. The most common type of unit in the trout tectum and optic nerve is trichromatic, with ON inputs from the long and short cone me chanisms and an OFF input from the medium mechanism. In contrast, gold fish color vision is dominated by L and M opponent units without S inp ut. The segregation of ultraviolet sensitivity in the torus but not in the tectum relates to functional differences of these two areas. Whil e the tectum serves the function of wavelength discrimination, ultravi olet inputs to the torus may contribute to prey detection and orientat ion.