Drivers of cannibalism in early juvenile Japanese mitten crabs Eriocheir japonica under laboratory conditions

Although the Japanese mitten crab Eriocheir japonica exhibits high potential for aquaculture, cannibalism under rearing conditions limits productivity. However, a quantitative evaluation of the factors driving cannibalism remains lacking for the early juvenile stages, which constitute the most critical stage for aquaculture. Here, we aimed to quantitatively evaluate the combined effects of size ratio, mean size, food treatment (fed versus starved), molting, and elapsed days on the risk of cannibalism in early juveniles using a Bayesian multinomial mixed-effects model. The probability that the smaller individual was cannibalized significantly increased with a larger size ratio between individuals, starved treatment, and increasing elapsed days. Furthermore, the molting of the smaller individual in a crab pair significantly elevated its risk of being cannibalized. In contrast, cannibalism slightly decreased in pairs composed of larger individuals, and it was strongly suppressed when the larger individual had molted. It was extremely rare for the larger individual in a pair to be the victim. Our findings suggest that cannibalism in early juvenile Japanese mitten crabs is a context-dependent foraging strategy based on a cost–benefit trade-off. These quantitative insights provide a foundational basis for developing specific husbandry guidelines to mitigate cannibalism in Japanese mitten crabs in aquaculture.