Effect of body size on cannibalism in juvenile mud crab Scylla serrata (Decapoda: Brachyura: Portunidae) under laboratory conditions

抄録

Cannibalism is considered a major cause of mortality among juveniles in nursery cultures of the mud crab Scylla serrata. Size grading is recommended as an effective measure to mitigate cannibalistic behavior; however, little is known about how body size differences influence cannibalistic episodes between juvenile individuals. We conducted one-to-one match experiments using hatchery-raised juveniles with carapace width between 12.5 and 33.3 mm. Two crabs were placed in an experimental arena for 24 h, and survival and pereiopod loss were subsequently observed. Large crabs always preyed on small crabs, and the probability of cannibalistic behavior significantly increased with the increasing relative size difference [RSD=1−(size of small crab)/(size of large crab)]. The loss of chelipeds and walking legs in the surviving small crabs amounted to 25% and 38%, respectively, and the proportion of lost walking legs increased with the increasing RSD, indicating the stronger aggressive behavior of larger crabs. This study suggests that maintaining size differences below the RSD threshold (0.34) at which 50% of the small crabs are cannibalized by large crabs would be an effective strategy to contain the occurrence of cannibalism in mud crab nursery cultures.