Changes in Intestinal Histology and Microbiota of Exopalaemon carinicauda Induced by Exposure to Alexandrium pacificum

Alexandrium pacificum is a typical harmful dinoflagellate in aquatic ecosystems that produces paralytic shellfish toxins (PSTs). While PSTs are well known for bioaccumulating in shellfish and posing severe food-safety risks to human consumers, their direct impacts on other aquatic species, such as shrimp, remain poorly studied. The current study investigated the damage caused by A. pacificum to the intestinal tissues of Exopalaemon carinicauda. For this purpose, adult E. carinicauda were divided into a control group and two experimental groups, with the latter involving a seven-day exposure to 0.5 × 104 and 1.0 × 104 A. pacificum cells/mL, respectively. Histological analyses subsequently showed obvious pathological alterations, including an irregular morphology and loosened inter-tissue connections, within the intestinal tissues of the exposure groups. Additionally, oxidative stress-related genes (Sod2, HSP70 12A, HSP90) were significantly upregulated, while cat, Gtpx and GSTM4 were significantly downregulated. The relative expression of Crustin, ALF and proPO3 decreased, whereas that of LGBP, TNFAIP-like and casp3 increased. Finally, analysis of the intestinal microbiota revealed that exposure to A. pacificum could also induce alterations in the intestinal microbial community, as reflected by a lower α-diversity, a high abundance of Proteobacteria and Vibrionaceae as well as functional predictions indicating suppressed metabolic pathways such as energy metabolism. The findings indicated that exposure to A. pacificum may induce histopathological and microbiota changes in E. carinicauda intestines, along with oxidative stress and changes in immune responses. This study reveals the negative impacts of A. pacificum on the intestinal health of E. carinicauda, which should be carefully considered and analyzed in aquaculture practices.