Background colour preference in juvenile European lobster ( <i>Homarus gammarus</i> )

The European lobster (Homarus gammarus) is a commercially valuable species under pressure from overfishing, climate change, and offshore developments. As hatchery-based restocking and aquaculture expand, optimising artificial rearing conditions, particularly environmental factors like habitat colouration, has become critical to improving welfare and production efficiency. To address this knowledge gap, the present study analysed the preference of background colour in juvenile (post-stage V) European lobsters (0.125±0.022 g lobster-1, 9.350±0.669 mm (mean±SD) carapace length). Bespoke triangle segments were produced using 3D printing with different-coloured plastic filaments and assembled into hexagonal chambers, with the triangle segments in various colours. In sub-trial 1, each chamber included one of six colours: black, red, blue, green, white, and yellow. Lobster behavioural responses were measured using three metrics: time spent (duration), number of incidental movements, and final colour settlement. These metrics had five behavioural parameters: Mean duration, Total duration, Colour preference ratio, Final colour settlement and Incidental movement. Through assessing these metrics and behavioural parameters, it was revealed that lobsters had a similar significant preference for black and red background colour. To discern whether there is a higher preference for one colour over the other, sub-trial 2 was undertaken, using equal black and red segments to make up the hexagonal chamber. Sub-trial 2 indicates that the preference for red is marginally greater than black under the same metrics. The present study contributes to a better understanding of the environmental preferences of juvenile European lobsters, providing insights that can inform the design of aquaculture systems and support improved animal welfare.