Background colour preference in juvenile European lobster (Homarus gammarus).

The European lobster (Homarus gammarus) is a commercially valuable species facing increasing anthropogenic pressure. As hatchery-based restocking and aquaculture expand, optimising artificial rearing conditions, particularly environmental factors like habitat colouration are essential for improving welfare. The present study investigated background colour preference in juvenile (poststage V) lobsters. Custom triangle segments were 3D printed with different-coloured filaments and assembled into hexagonal chambers. In sub-trial 1, each chamber contained six colour: 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. An assessment of these metrics and behavioural parameters revealed that lobsters had a similarly significant preference for black and red background colours. To discern whether there is a higher preference for one colour over the other, sub-trial 2 was performed, using equal black and red segments. Sub-trial 2 indicates that the preference for red is marginally greater than black under the same metrics. These findings contribute to a better understanding of lobster environmental preference and can inform the design of aquaculture systems to enhance animal welfare.