Alternative Splicing Events and Differently Expressed Genes During Peak Mortality in Large Yellow Croaker (Larimichthys crocea) Infected with Scuticociliate.

Large yellow croaker (Larimichthys crocea) is facing various threats from bacterial, viral, and parasitic diseases, especially scuticociliate. Scuticociliate is a facultative parasite causing high mortality in various marine fishes. In this study, an artificial scuticociliate infection model was successfully established for large yellow croaker. Comparative transcriptome analysis was performed on gill tissues collected from control fish and fish at the peak of mortality following exposure to the parasite to investigate the underlying molecular mechanisms of host-parasite interactions. A total of 400, 427, and 311 differential alternative splicing (DAS) events were identified at 7 d/0 h, 8 d/0 h, and 9 d/0 h, respectively. Meanwhile, 761 differentially expressed genes (DEGs) were found, with 154 simultaneously at three time points. GO and KEGG enrichment analysis showed that DAS genes and DEGs were mainly focused on self-respire, immune, and metabolic-related pathways. The DEGs related to blood coagulation included fga, fgb, fgg, and lectin domain genes. Lectin domain genes were also involved in reducing parasite burden. Cytokines, Caspase-1, trim13, trim16, and trim39 co-participated in immune response. Notably, the complement component gene c3 was both a DEG and underwent DAS. Using STRING software, interaction regulatory networks were constructed to visualize potential hub genes, revealing 22 DEGs shared across at least two time points. These findings provide valuable insights into the immune and metabolic responses of large yellow croaker to scuticociliate infection, offering a foundational reference for identifying resistant genes and understanding fish-parasite interactions.