Based on the limited hepatic hydroxylation efficiency of dietary VD3 in teleosts and the superior bioavailability of its metabolite, 25(OH)D3, this study investigated the regulatory mechanisms of dietary 25(OH)D3 supplementation in yellow catfish—an economically significant species lacking prior nutritional data on this metabolite. A total of 360 fish were divided into three groups—control (basal diet), VD3 (2500 IU/kg VD3), and 25(OH)D3 (2500 IU/kg 25(OH)D3)—and fed for 8 weeks. Compared to the control, both supplemented groups showed elevated superoxide dismutase (SOD), total antioxidant capacity (T-AOC), catalase (CAT), and transforming growth factor-β (TGF-β) activities, alongside reduced malondialdehyde (MDA), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) levels. The 25(OH)D3 group exhibited higher T-AOC and CAT activities and lower TNF-α than the VD3 group. Metabolomic and transcriptomic analyses identified 65 differentially expressed metabolites (DEMs) and 3515 differentially expressed genes (DEGs). Enrichment analysis indicated that the DEMs (e.g., indole compounds, organic acids, aldosterone, L-kynurenine) and DEGs (pgd, mthfr, nsdhl, nox5, prdx2, mpx, itih2, itih3, eprs1) that were highly and significantly expressed in the 25(OH)D3 group were primarily associated with antioxidant defense and inflammatory responses. Dietary 25(OH)D3 was more effective than VD3 in promoting antioxidant capacity and modulating inflammation in yellow catfish.

The Chinese sturgeon (Acipenser sinensis) is an ancient, complex autooctoploid fish species that is currently facing conservation challenges throughout its distribution. To comprehensively characterize the expression profiles of genes and their associated biological functions across different tissues, we performed a transcriptome-scale gene expression analysis, focusing on housekeeping genes (HKGs), tissue-specific genes (TSGs), and co-expressed gene modules in various tissues. We collected eleven tissues to establish a transcriptomic repository, including data from Pacific Biosciences isoform sequencing (PacBio Iso-seq) and RNA sequencing (RNA-seq), and then obtained 25,434 full-length transcripts, with lengths from 307 to 9515 bp and an N50 of 3195 bp. Additionally, 20,887 transcripts were effectively identified and classified as known homologous genes. We also identified 787 HKGs, and the number of TSGs varied from 25 in the liver to 2073 in the brain. TSG functions were mainly enriched in certain signaling pathways involved in specific physiological processes, such as voltage-gated potassium channel activity, nervous system development, glial cell differentiation in the brain, and leukocyte transendothelial migration in the spleen and pronephros. Meanwhile, HKGs were highly enriched in some pathways involved in ribosome biogenesis, proteasome core complex, spliceosome activation, elongation factor activity, and translation initiation factor activity, which have been strongly implicated in fundamental biological tissue functions. We also predicted five modules, with eight hub genes in the brown module, most of which (such as rps3a, rps7, rps23, rpl11, rpl17, rpl27, and rpl28) were linked to ribosome biogenesis. Our results offer insights into ribosomal proteins that are indispensable in ribosome biogenesis and protein synthesis, which are crucial in various cell developmental processes and neural development of Chinese sturgeon. Overall, these findings will not only advance the understanding of fundamental biological functions in Chinese sturgeon but also supply a valuable genetic resource for characterizing this extremely important species.

Ichthyophthirius multifiliis poses a significant threat to global aquaculture, yet some fish species exhibit remarkable resistance. This study employed a combined LC-MS-based metabolomics and 16S rRNA gene sequencing approach to investigate the intrinsic mechanisms underlying the differential susceptibility of Percocypris pingi, crucian carp, and yellow catfish. Our results revealed distinct skin molecular and microbial profiles in P. pingi associated with its enhanced resilience. Metabolomic analysis identified a significant upregulation of key antioxidants (L-Glutathione reduced, L-Glutathione oxidized, L-Cysteine-glutathione gisulfide, Uric acid, Histamine, N-Acetylhistamine, and scorbic acid) in P. pingi, most notably L-Glutathione reduced, which was 31- and 59-fold higher than in yellow catfish and crucian carp, respectively. Functional enrichment further highlighted the critical role of enhanced antioxidant capacity (centered on glutathione metabolism) and immune/inflammatory responses in the resistance to I. multifiliis of P. pingi. Concurrently, skin microbiome analysis showed that P. pingi hosted a microbial community distinct from the other two species, with significantly higher α-diversity. Notably, P. pingi skin was significantly depleted of the parasitic bacteria Candidatus_Megaira and Candidatus_Midichloria, which were highly abundant in the susceptible species. Furthermore, predicted metagenomic functions indicated that P. pingi’s microbiota was enriched in fundamental metabolic pathways, whereas the microbiota of crucian carp and yellow catfish was skewed towards disease- and immune-related pathways. In conclusion, our findings demonstrate that the superior resistance of P. pingi to I. multifiliis is likely conferred by a synergistic effect of a robust skin antioxidant capacity (primarily driven by glutathione) and a protective skin microbiome that excludes specific parasites. This study provides novel insights into the multi-faceted mechanisms of disease resistance in fish.