Effect of low-temperature stress on transcriptome and Na+/K+-ATPase changes in Oreochromis niloticus gill tissues

Low temperatures limit the development of Oreochromis niloticus (tilapia), and an increase in low-temperature tolerance would increase yields. We studied the responses of tilapia to low temperatures. The fish were labeled CK, AA, BB, and CC based on treatment (25 degrees C, 12 degrees C/1 h, 12 degrees C/24 h, and 12 degrees C/48 h, respectively) with CK being the control group. We examined the transcriptome responses and the Na+/K+-ATPase activity of gill tissue in each group. The Na+/K+-ATPase activity varied with the treatment time. Transcriptome sequencing of 12 individuals yielded 585.51 million clean reads, and at least 83.26% of the genes were mapped to the reference genome. Comparative analysis revealed 12,448 genes with significantly differential expression, including 792, 1,827, and 1,924 upregulated genes and 992, 3,056, and 3,857 genes downregulated for AA, BB, and CC, respectively. Differentially expressed genes (DEGs) were validated using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for five genes. Functional annotation analysis of the DEGs identified functions associated with response to low-temperature stress. When tilapia was subjected to low-temperature stress, expression changes occurred in genes associated with cytokine-cytokine receptor interaction, metabolic pathways, cell adhesion molecules, material transport, and immunity. The finding will help understand the effects of low temperatures on fish and provide a theoretical basis for the tilapia breeding industry.