The effect of metal halide and novel green cathode lights on the stress response, innate immunity, eye structure and feeding activity of Atlantic cod, Gadus morhua L.

High-intensity constant lighting is routinely used for photoperiod manipulation in the aquaculture industry in order to prevent early maturation. The potential welfare impacts of this technology, however, have not been extensively studied to date, and with the implementation of more efficient narrow bandwidth lighting technologies (cathode, light-emitting diodes), definitions of species-specific sensitivities are becoming essential. The objective of this study was to investigate the impact of traditional metal halide (MH) and novel green cathode lighting on the welfare (stress response, innate immunity, retina structure, feeding activity) and light perception of Atlantic cod. The results indicated that although acute responses to light were observed, there were no clear significant long-term effects of any of the lighting treatments on the stress levels (plasma cortisol, glucose), innate immune function (lysozyme activity), retina structure and population feeding activity (acute decline under all light treatments, most pronounced in fish exposed to higher illumination, but normal feeding activity was resumed within 8 days following light onset). Regarding light perception, interestingly, even when subjected to high-intensity constant lighting (MH mean tank intensity: 16.6Wm-2), cod still demonstrated a day-night rhythm in melatonin release, which suggests perception of the overlying ambient photoperiod.