Temperature-dependent shell disease may relate to bacterial community changes of mud crab Scylla paramamosain in RAS

Abstract

The previous study found that recirculating aquaculture system (RAS) in which temperature could be controlled was a feasible method for S. paramamosain to overwinter, but shell disease occurred during the overwintering process (12 °C–20 °C). Therefore, this study explored how temperature affected the occurrence of crab shell disease and potential pathogens, providing guidance for the overwintering management of S. paramamosain. This study investigated the prevalence of shell disease of S. paramamosain and analyzed the bacterial community dynamics in water and on the carapace under different overwintering temperatures (12, 16, and 20 °C) over 8 weeks. Shell disease incidence increased with temperature (P < 0.05), peaking at 86.7 ± 23.1 % in the 20 °C group. Lesions primarily appeared on the dorsal carapace and were characterized by melanization, structural damage, and bacterial colonization. Bacterial diversity in water remained stable across temperatures (P > 0.05), but carapace bacterial richness and phylogenetic diversity declined significantly at 20 °C (P < 0.05). The bacterial community structure differed across temperature groups (P < 0.05), with the relative abundance of Aquimarina, particularly Aquimarina penaei (ZOTU 92), rising on the carapace at 20 °C (P < 0.05). Functional prediction indicated a significant increase in chitin deacetylase activity at 20 °C (P < 0.05), suggesting that bacterial degradation of the carapace may be enhanced. Additionally, while the bacterial co-occurrence network on the carapace at 20 °C was complex, its stability declined. The interaction of bacterial communities between water and carapace also became increasingly intricate with rising temperatures. To our knowledge, this is the first study to establish a link between shell disease and overwintering temperature in mud crabs.