Identification of differentially expressed genes in gills of tiger puffer (Takifugu rubripes) in response to low-salinity stress.

Salinity is an important abiotic factor for aquatic organisms. In fish, changes in salinity affect physiological responses and alter the immune system. Takifugu rubripes is an important economic marine fish, and mechanisms of T. rubripes adaptation to salinity changes need to be further documented. In this study, a transcriptome sequencing technique was used to analyse genes that were differentially expressed in the T. rubripes gill after low-salinity stress for 30 d, and differential gene expression was further validated by quantitative real-time PCR (qPCR). After assembly, 385 differentially expressed genes (DEGs) were identified, including 182 upregulated genes and 203 downregulated genes. The DEGs were assigned to Gene Ontology (GO) classes with a total of 1647 functional terms. Most DEGs were assigned to biological process (984; 59.8%) followed by molecular function (445; 27.0%) and cellular component (218; 13.2%). Further KEGG analysis allocated 385 DEGs to 95 KEGG pathways. After q-value correction, 7 pathways (Glycolysis/Gluconeogenesis; Biosynthesis of amino acids; Carbon metabolism; Fructose and mannose metabolism; Pentose phosphate pathway; Metabolism of xenobiotics by cytochrome P450; and Glycine, serine and threonine metabolism) remained significant. qPCR results indicated that the transcripts of six selected genes sharply increased after 30 d of low-salinity stress. Low-salinity stress obviously increased SLC39A6, SLC5A9, NKAα1, CYP1A1, CYP1B1, and GSTA expression. In contrast, the genes encoding Aldoaa, GPI, FBP2 and GAPDH exhibited downregulation. In addition, three solute carrier (SLC) genes selected from the DEGs were further studied for differential expression patterns after low-salinity exposure, and the results showed that the SLCs were upregulated in T. rubripes after 72 h of low-salinity exposure. This investigation provides data for understanding the molecular mechanisms of fish responses to low-salinity stress and provides a reference for rationally setting salinity levels in aquaculture.