While contributing to the conservation of natural fish stocks, the aquaculture sector imposes environmental repercussions. The growing popularity of colour-graded eco-labels in promoting pro-environmental practices in food production underscores the need for scientific insights into consumer responses to such labels, particularly with the imminent prospect of a harmonized European labelling framework. The existing literature, although limited and divergent, advocates for real-life testing with fresh, perishable food products, emphasizing the inadequacy of standalone labels and the necessity for complementary measures. Furthermore, the mechanisms underlying how consumers process multi-coloured Front-of-Pack (FOP) labels remain ambiguous, with uncertainties regarding induced consumption shifts stemming from both deliberate information processing and less deliberate associations. This article presents findings from a randomized control trial conducted in a simulated fishmonger store in Derio, Bizkaia, Spain, involving 200 consumers. Participants selected various sea bass products out of multiple options. This task was subject to a 2 (Enviroscore: with vs without) x 2 (Supporting info on Enviroscore: with vs without) between-subject design, resulting in four treatment groups. A 16% increase in the likelihood of selecting lower-impact products was observed. Notably, this effect was evident only in the absence of supporting information on Enviroscore, and the observed impact could not be attributed to any indirect attention effect. In conclusion, Enviroscore exhibits potential in steering consumer choices toward more environmentally friendly aquaculture fish options, even in physical retail settings. However, these effects may be rooted in unconscious responses rather than deliberate environmental considerations, raising questions about the suitability of envisaged policy orientations encompassing disaggregated environmental, nutritional, animal welfare, and social welfare scores. Generalization of these findings warrants validation through further research encompassing a more comprehensive range of products.