Animals evolve behavioural strategies throughout life to increase their chances of survival in nature. The activity pattern and behaviour of juveniles of the commercial tropical sea cucumber Stichopus cf. horrens were examined in view of factors that may influence survival at this critical stage of development. Wild juveniles were observed in the field to describe diel activity and movement rates. Activity of wild and hatchery-reared juveniles was observed in the laboratory to examine periodicity under artificial conditions and the influence of light and microhabitat on feeding and sheltering behaviour. Behaviour was evaluated under different light cycle treatments and with different microhabitats as shelter options. Overall, wild and hatchery-reared juveniles (4-54 g) displayed a distinct nocturnal activity pattern both in situ and under laboratory conditions. Nocturnal activity was strongly associated with feeding and locomotion. Wild and hatchery-reared juveniles fed most actively at night, displayed intermediate activity during twilight, and minimal to no activity during daytime. Movement rates of wild juveniles in the field was significantly influenced by time of day and size to a lesser extent. Under constant light and constant dark conditions for 48 h, the feeding rhythm of juvenile S. cf. horrens was controlled endogenously and was strongly entrained to natural light-dark cycles. Sheltering was directly affected by light and associated with strong phototactic and thigmotactic reflexes. Juveniles preferred vegetation as shelter relative to coral boulders, bare sand or open space. When presented with two types of vegetation, juveniles showed equal preference for seagrass and macroalgae as shelter. Deviations in the behaviour of hatchery-reared juveniles under different light conditions indicate some degree of acclimation to an artificial environment with minimal threats and a decreased sensitivity to light. The implications of nocturnal feeding, light-induced sheltering, shelter preferences and acclimation to artificial conditions of juvenile S. cf. horrens are discussed in relation to growth and survival in nature and in the context of potential culture and restocking of the species.