Behavioural effects of artificial light on fish species of commercial interest

The aim of this study was to investigate the effects of artificial light of variable intensity and wavelength on aggregation, phototaxis and photokinesis in the European seabass Dicentrarchus labrax, the common grey mullet Mugil cephalus, the gilthead seabream Sparus auratus and the striped bream Lithognathus mormyrus. Two sets of experiments were carried out in laboratory conditions: during the first set light intensity was either increased or decreased in eight discrete steps, in the range 0.2-68 μE s−1 m−2. During the second set light colour was shifted either from the shorter to the longer wavelengths of the visual spectrum or back, using six different colour filters. Overall, the common grey mullet and the gilthead seabream showed the strongest attraction to light. Such a positive response was enhanced by the mode of intensity variation. The striped bream tended to be attracted to light at all illumination levels. Instead, the European seabass was neither particularly attracted nor inhibited by the presence of light. The grey mullet showed a strong positive response also to monochromatic stimuli, especially of shorter wavelength. The seabass was noticeably affected by shorter wavelength lights as well. However, in this case colours such as blue and green induced strong repulsion. Similarly, the seabream was conspicuously repelled by monochromatic lights. The striped bream did not show any remarkable reactions to coloured lights. These results contributed to the ecological classification of species according to their visual behaviour patterns towards artificial light. Such findings may provide useful suggestions for the development of selective light fishing techniques. The rationalisation of light fishing on a large scale would help to improve the quality of marine environment management both in exploited and in novel fishing grounds.