Spectral sensitivity of the two-spotted goby Gobiusculus flavescens (Fabricius): a physiological and behavioural study.

Microspectrophotometry of Gobiusculus flavescens photoreceptors revealed a single rod visual pigment (lambdamaxat 508 nm) and the three cone pigments (lambdamax 456, 531 and 553 nm). The cone population was dominated by identical double cones containing the middle-wave-sensitive (MWS) pigment, but with a small number of non-identical MWS/LWS (long-wave-sensitive) and identical LWS double cones. Small populations of large single cones also contained either the MWS or LWS pigment. The short-wave-sensitive (SWS) pigment was found in small single cones. Lens transmission was great reduced below 410 nm. The spectral sensitivity of the behaviourally determined reaction distance (RD) to prey at a high irradiance level (0.5 micromol m-2 s-1) correlated with the maximum sensitivity of the MWS cones, both peaking around 530 nm. However, at a lower irradiance level (0.015 micromol m-2 s-1) such a correlation was not so apparent. The RD was greatly reduced, though still maintaining a peak around 530-550 nm, but with a relatively smaller reduction in RD at shorter wavelengths. Optomotor behaviour displayed a somewhat similar spectral sensitivity to the RD responses at the higher light intensity. However, the peak was at slightly longer wavelengths at 550 nm, suggesting a greater input from LWS cones to the optomotor response.