Introduction: In August 2023, hybrid sturgeons (Acipenser baerii♀×Acipenser schrenckii♂) cultured in Sichuan, China, showed infectious disease symptoms, including ulcers, liver and spleen nodules, and high mortality rates.Methods: Pathogenic bacteria were isolated from the liver of diseased sturgeons and analyzed for their phenotypic and molecular traits. Furthermore, iridovirus-specific TaqMan real-time PCR (RT-PCR) analyses were conducted. The histopathological characteristics were analyzed using paraffin sectioning and transmission electron microscopy (TEM). Transcriptome sequencing was performed to elucidate the impact of pathogen exposure and immune response profiles in infected sturgeon.Results: Pathogenic bacteria isolation and phylogenetic analyses of the 16S rRNA gene confirmed that the isolated bacteria clustered within the Nocardia seriolae group. The TaqMan RT-PCR assay was performed to detect the presence of white sturgeon iridovirus (WSIV), indicating a weakly positive signal. Histopathological examination revealed severe damage to various tissues, and a notable presence of bacteria was observed through acid-fast staining. Transmission electron microscopy analysis showed the presence of abundant bacteria and virus particles, indicating cellular invasion and subsequent damage. In summary, the disease in hybrid sturgeons was diagnosed as infection of N. seriolae and WSIV. To investigate the immune response of hybrid sturgeons to this infection, spleen transcriptomes were analyzed. Numerous immune-related genes and pathways, including the “Toll-like receptor”, “B-cell receptor”, and “T-cell receptor” signaling pathways, were altered in response to pathogenic threats. Significantly downregulated of key components of TCR and BCR signaling pathways, such as ZAP70, BTK, and CD79A, suggested a temporary inhibition of these pathways critical for cellular immunity post-infection. Gene set enrichment analysis revealed significant suppression of the apoptosis signaling pathway and activation of autophagy and mitophagy signaling pathways following infection. Specifically, in the death receptor-mediated apoptosis signaling pathway, downregulation of TNFα, TRAIL, CASP6, and CASP8 was observed, while several genes in the autophagy and mitophagy pathways showed upregulated expression post-infection.Discussion: We report the initial occurrence of N. seriolae infection in cultured sturgeons. These findings could provide a theoretical basis for diagnosing and preventing this disease, as well as enhance the understanding of host-pathogen interactions in fish.

The hybrid sturgeon Acipenser baerii × A. schrenckii is the most widely cultured commercial sturgeon in China. However, its morphological similarity to the parental species frequently leads to misuse of germplasm in the breeding process, resulting in a decline in the quality of the sturgeon production. In this study, we have developed a protocol by using mitochondrial DNA barcoding and microsatellite locus analysis for the accurate identification of sturgeon species. Genetic distance and phylogenetic analysis based on the mitochondrial COI segment showed that A. baerii exhibited the closest genetic relationship with orthogonal individuals A. baerii (♀) × A. schrenckii (♂). Conversely, A. schrenckii displayed the highest genetic similarity with reciprocal individuals A. schrenckii (♀) × A. baerii (♂). Additionally, genetic structure analysis and factor correlation analysis (FCA) were conducted using six microsatellite loci among 100 samples, including eight species and two hybrid sturgeon. The results showed that all samples, encompassing both hybrid sturgeon (A. baerii × A. schrenckii) and their parental species, were accurately grouped into ten clusters, thereby validating the precision of this species assignment method.

This study aimed to investigate the histological features of the intestine of Acipenser dabryanus from 1 to 15 months of age via HE staining, AB-PAS staining, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The intestine of A. dabryanus comprises the duodenum, spiral valve intestine, and rectum. With age, the duodenal diameter and mucosal/muscular layer thickness increased, the spiral valve intestine’s mucosa thickened and protrusions formed networks, and the rectal diameter enlarged. Abundant mucus cells, predominantly type IV, were found in the duodenum, spiral valve intestine, and rectum of A. dabryanus at different ages by AB-PAS staining. Our study confirmed the presence of ciliated columnar cells (with ‘9 + 2’ cilia structure) with orderly arranged cilia at their apices in the mucosal epithelium of A. dabryanus’s duodenum, spiral valve intestine, and rectum for the first time, as shown by SEM and TEM. The presence of spiral valves and ciliated columnar cells in the intestinal structure of A. dabryanus highlights its unique features and evolutionary significance. These findings highlight A. dabryanus’s unique intestinal features and evolutionary significance, providing a basis for scientific feed formulation and enhancing our understanding of the histological characteristics of the sturgeon intestine.

This study investigated muscle quality differences between wild-type (WT) and yellow-mutant (YM) Triplophysa siluroides. Texture analysis showed WT T. siluroides had significantly greater hardness, gumminess, and resilience than YM. Histological and biochemical analyses ruled out myofiber diameter/density as drivers, instead identifying reduced collagen in YM as key, as confirmed by Picrosirius red staining, collagen quantification, and transmission electron microscopy. Transcriptomic and proteomic analyses revealed that TGF-β/BMP pathway suppression in YM resulted in downregulation of core molecules (e.g., BMP2 and SMAD1), collagen-related genes (e.g., COL1A1a and COL1A1b), and ECM-related genes (e.g., TNC and FN1), potentially influencing collagen synthesis and ECM homeostasis. Notably, melanin gene TYRP1 was also downregulated in YM T. siluroides, suggesting a link between pathway suppression, muscle quality alteration, and body pigmentation. The potential role of the BMP2-SMAD1-TYRP1 axis in the association between muscle quality and body colour provides novel mechanistic insights, offering molecular targets for the breeding of T. siluroides with superior commercial traits.