Spotted scat (Scatophagus argus) can tolerate a wide range of salinity fluctuations. It is a good model for studying environmental salinity adaptation. Lipid metabolism plays an important role in salinity adaptation in fish. To elucidate the mechanism of lipid metabolism in the osmoregulation, the liver transcriptome was analyzed after 22 d culture with a salinity of 5 ppt (Low-salinity group: LS), 25 ppt (Control group: Ctrl), and 35 ppt (High-salinity group: HS) water by using RNA sequencing (RNA-seq) in spotted scat. RNA-seq analysis showed that 1276 and 2768 differentially expressed genes (DEGs) were identified in the LS vs. Ctrl and HS vs. Ctrl, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the pathways of steroid hormone biosynthesis, steroid biosynthesis, glycerophospholipid metabolism, glycerolipid metabolism, and lipid metabolism were significantly enriched in the LS vs. Ctrl. The genes of steroid biosynthesis (sqle, dhcr7, and cyp51a1), steroid hormone biosynthesis (ugt2a1, ugt2a2, ugt2b20, and ugt2b31), and glycerophospholipid metabolism (cept1, pla2g4a, and ptdss2) were significantly down-regulated in the LS vs. Ctrl. The pathways related to lipid metabolisms, such as fatty acid metabolism, fatty acid biosynthesis, peroxisome proliferator-activated receptor (PPAR) signaling pathway, adipocytokine signaling pathway, fatty acid degradation, and unsaturated fatty acid biosynthesis, were significantly enriched in the HS vs. Ctrl. The genes of unsaturated fatty acid biosynthesis (scd1, hacd3, fads2, pecr, and elovl1) and adipocytokine signaling pathway (g6pc1, socs1, socs3, adipor2, pck1, and pparα) were significantly up-regulated in the HS vs. Ctrl. These results suggest that the difference in liver lipid metabolism is important to adapt to low- and high-salinity stress in spotted scat, which clarifies the molecular regulatory mechanisms of salinity adaptation in euryhaline fish.

Somatostatins (SSTs) are a family of proteins consisting of structurally diverse polypeptides that play important roles in the growth regulation in vertebrates. In the present study, four somatostatin genes (SST1, SST3, SST5, and SST6) were identified and characterized in the spotted scat (Scatophagus argus). The open reading frames (ORFs) of SST1, SST3, SST5, and SST6 cDNA consist of 372, 384, 321, and 333 bp, respectively, and encode proteins of 123, 127, 106, and 110 amino acids, respectively. Amino acid sequence alignments indicated that all SST genes contained conserved somatostatin signature motifs. Real-time PCR analysis showed that the SST genes were expressed in a tissue specific manner. When liver fragments were cultured in vitro with synthetic peptides (SST1, SST2, or SST6 at 1 μM or 10 μM) for 3 h or 6 h, the expression of insulin-like growth factor 1 and 2 (Igf-1 and Igf-2) in the liver decreased significantly. Treatment with SST5 had no significant effect on Igf-1 and Igf-2 gene expression. This study provides an enhanced understanding of the gene structure and expression patterns of the SST gene family in S. argus. Furthermore, this study provides a foundation for future exploration into the role of SST genes in growth and development.

The spotted scat (Scatophagus argus) is the most widely commercially cultured fish in eastern and southern Asia that possess potential economic value. However, up to date, there are no studies reported on the selection of suitable reference genes in this fish, which is crucial for guaranteeing accurate and reliable results in RT-qPCR analyses. This study aimed at screening the most stable reference genes in the ovary and pituitary at different ovarian stages, which is of great significance for further research on the reproductive regulation mechanism of female S. argus. In this study, we selected twenty-one genes as the candidate reference genes, including four genes in the ovary (EEF1A, ACTB, B2M, and HPRT1), and seventeen genes in the pituitary (B2M, APOA1, CGBA, RPLP0, GNRHR, GUSB, TBP, SLC25A5, RPL4, PLA1A, GAPDH, GNB2L1, CTFS, HPRT1, RPS2, TFRC, and TUBB4B). To analyze the stability of the potential reference genes, we first used four commonly used software, BestKeeper, GeNorm, NormFinder, and ΔCt, and then we established comprehensive rankings with ReFinder. The results indicate that RPL4 and GNB2L1, and EEF1A and HPRT1 were the most appropriate reference genes for the pituitary and ovary of S. argus, respectively, in the three developmental stages of the ovary. Additionally, GeNorm analysis suggested that for the accurate normalization of gene expression, two reference genes were reliable in the ovary and pituitary of S. argus. To the best of our knowledge and understanding, this is the first study to identify appropriate reference genes for analyzing gene expression in S. argus. Consequently, this study can be used as a foundation for future research on the reproduction of S. argus.