The brain is considered to be an extremely sensitive tissue to hypoxia, and the brain of fish plays an important role in regulating growth and adapting to environmental changes. As an important aquatic organism in northern China, the economic yield of Takifugu rubripes is deeply influenced by the oxygen content of seawater. In this regard, we performed RNA-seq analysis of T. rubripes brains under hypoxia and normoxia to reveal the expression patterns of genes involved in the hypoxic response and their enrichment of metabolic pathways. Studies have shown that carbohydrate, lipid and amino acid metabolism are significant pathways for the enrichment of differentially expressed genes (DEGs) and that DEGs are significantly upregulated in those pathways. In addition, some biological processes such as the immune system and signal transduction, where enrichment is not significant but important, are also discussed. Interestingly, the DEGs associated with those pathways were significantly downregulated or inhibited. The present study reveals the mechanism of hypoxia tolerance in T. rubripes at the transcriptional level and provides a useful resource for studying the energy metabolism mechanism of hypoxia response in this species.

The purpose of this study was to explore the genetic diversity, genetic structure, and phylogenetic relationships of different cultured populations of Takifugu rubripes and T. obscurus in China, and to find a DNA barcode that can effectively distinguish one species from the other. In total, 120 T. rubripes and 130 T. obscurus individuals were collected from four and three different regions, respectively. Based on the sequences of the mitochondrial genes COI, COII, COIII, 16S rDNA, and Cytb, the genetic diversity and genetic evolution of the different populations of T. rubripes and T. obscurus were analyzed, and the genes with more polymorphic loci and high genetic diversity were selected for DNA barcoding for the identification of the two species. The results showed that Cytb had the highest genetic diversity, consistent with the genetic diversity of the other four genes. T. rubripes and T. obscurus have low haplotype and diversity indices, indicating that they may be subjected to variety of processes, such as inbreeding or domestication, that could lead to a continuous decline in diversity. From the perspective of differentiation and phylogeny, gene exchange may occur between some of the studied populations. Many populations of T. rubripes and T. obscurus showed limited variation, indicating that they reproduce according to the neutral evolution model, and that their diversity cannot be improved. In addition, the Cytb gene fragment used can effectively distinguish T. rubripes from T. obscurus, which can provide support for species identification and breeding in the future.