Wavelength discrimination of the goldfish in the ultraviolet spectral range

Wavelength discrimination ability of the goldfish was measured with a behavioural training technique in the UV spectral range. First, spectral sensitivity was determined for the two fish to adjust the monochromatic lights (between 334 and 450 nm) to equal subjective brightness. The results of the wavelength discrimination experiment show that, independent of which wavelength the fish were trained on, the relative choice frequency reached values above 70% only at wavelengths longer than 410 nm. Wavelength discrimination between 344 and 404 nm was not possible. Accordingly, the delta lambda function increases steeply between 400 and 380 nm, with values between about 12 and 90 nm, respectively. Model computations indicate that the delta lambda function cannot be explained on the basis of the cone sensitivity spectra. Instead, inhibitory interactions have to be assumed which suppress the short wavelength flanks of the short-, mid-, and long-wavelength sensitive cone types in the UV range.