Developmental plasticity refers to an organism's ability to adjust its development in response to changing environmental conditions, leading to changes in behaviour, physiology, or morphology. This adaptability is crucial for survival and helps organisms to cope with environmental challenges throughout their lives. Understanding the mechanisms underlying developmental plasticity, particularly how environmental and ontogenetic factors shape functional traits, is fundamental for both evolutionary biology and conservation efforts. In this study we investigated the effects of early-life environmental conditions on the development of claw asymmetry in juvenile European lobsters (Homarus gammarus, N=244), a functional trait essential for survival and ecological success. Juveniles were randomly divided between four different rearing conditions characterized by the presence or absence of physical enrichments (e.g., substrate and shelters), which were introduced at different developmental stages in separated groups to assess the timing and nature of their effect. Results revealed that exposure to substrate alone, without additional stimuli, consistently promoted claw asymmetry, regardless of the timing of its introduction, while the 6th developmental stage emerged as the critical period for claw differentiation. By identifying the environmental factors that influence developmental outcomes in lobsters, and the timing of these effects, this study improves our understanding of developmental plasticity and offers valuable insights for optimizing conservation aquaculture and reintroduction strategies.