Abstract: To addressthe inherent limitations of large yellow croaker (Larimichthys crocea) as an experimental host for infection and immunity studies of Pseudomonas plecoglossicida. To identify a suitable experimental animal model, the present study employed the P. plecoglossicida NB2011strain isolated from diseased large yellow croaker to establish an infection model using goldfish (Carassius auratus), with susceptibility tests performed to determine the median lethal dose (LD₅₀). Goldfish were artificially infected via intraperitoneal injection with live bacterial suspension, and spleens were collected at 0, 2, 4, and 6d post-infection for histopathological and ultrastructural observations, along with comprehensive transcriptome analysis of the infected fish spleens. The results demonstrated that P. plecoglossicida NB2011successfully infected goldfish via intraperitoneal injection, causing symptoms similar to those observed in large yellow croaker, with distinct white nodules appearing in the spleens of infected fish. The LD₅₀ was determined to be 1.41×10⁷ cells/mL. Histopathological examination revealed irregular morphology of splenic cells, blurred boundaries between red and white pulp, hemosiderin deposition, and vacuolization in some cells. Ultrastructural observations using transmission electron microscopy showed numerous bacteria in the spleen during the acute infection phase, prominent autophagosome formation in tissue macrophages, and evidence of bacterial escape from phagocytes. Transcriptome analysis revealed dynamic changes in the host response to P. plecoglossicida infection, with the most dramatic alterations in host gene expression profile occurring during the early stage (within 2 days). A total of 4279 and 3102 differentially expressed genes (DEGs) were identified at 2 days post-infection with the wild-type strain and the attenuated mutant strain, respectively, with the number of down-regulated genes significantly exceeding that of up-regulated genes in both groups. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that DEGs in the wild-type strain-infected group were significantly enriched in immune processes such as innate immune response and defense response to bacteria, as well as in fundamental metabolic pathways including carbon metabolism and lipid metabolism. In contrast, DEGs in the attenuated mutant strain-infected group were more prominently enriched in pathways such as fatty acid metabolism and cofactor biosynthesis, suggesting that the wild-type strain effectively elicits the immune response in goldfish. This study preliminarily established an infection model of goldfish and characterized the immune response profile of goldfish against Pseudomonas plecoglossicida infection, providing an important foundation for further elucidation of the pathogenic mechanism of this bacterium and the development of attenuated vaccines.