Importance of substrate on welfare in swimming crab (Portunus trituberculatus) culture: A territorial behavior perspective

Concern for animal welfare in aquaculture is increasing. Environmental enrichment (EE) is an effective means to improve the welfare of animals, which is linked to their behavior. Territorial behavior includes interactions between animals and their environment and conspecifics, and can directly reflect the welfare status of cultured animals. To explore the influence of different substate, an important influence factor of EE, on welfare of swimming crab (Portunus trituberculatus), a behavior acquisition system was established. Moving trajectory, territory size, time budgeting, total number of territorial behaviors, and bouts of crabs in EE groups (sand substrate, sand and shell mixed substrate, and shell substate) and the control (hard bottom) group were calculated and analyzed. Furthermore, the territorial behavior score of crabs was calculated using PCA to estimate territoriality. According to the results, the presence of substrate EE effectively reduced the territoriality of the swimming crabs, and sand as substrate affected most significantly. In the control group, stereotypical behaviors of crabs (repeated movements for long periods) indicated a low welfare level. In the EE group, interactions with the substrate, including burying behavior, digging, etc., revealed a higher behavioral diversity, which demonstrated that a suitable EE could effectively improve the welfare of swimming crabs. In general, from the perspective of territorial behavior, the presence of substrate, especially sand, was an effective means of improving the welfare of cultured swimming crabs. •The presence of substrate effectively reduced the territoriality of the swimming crabs.•Suitable environmental enrichment could effectively improve the welfare of swimming crabs.•Crabs could regularly reform the substrates in which they live.•Territorial behavior may be a suitable index reflecting the condition of crabs.