HPX and bacterial infectious disease: To address these gaps, the present study aimed to (1) characterize the structural and phylogenetic relationships of Siberian sturgeon (A. baerii) HPX to vertebrate HPX orthologs and teleost Wap65 paralogs, including three-dimensional protein modeling; and (2) investigate both basal expression patterns (tissue distribution and ontogenetic stage) and differential expression in response to bacterial infection and thermal challenge.