Takifugu obscurus has relatively small gills and gill pores. Consequently, a relatively low respiratory capacity. This fish is thus easily negatively affected by the low levels of dissolved oxygen (DO) that are common in high-intensity aquaculture. In order to clarify the mechanisms underlying the hypoxia response of T. obscurus, we used liquid mass spectrometry (LC–MS) to identify and quantify the metabolites present in the T. obscurus gill under the following conditions: normoxia (DO, 7.0 ± 0.2 mg/L), hypoxia (DO, 0.9 ± 0.2 mg/L), and reoxygenation (4, 12, and 24 h after return to normoxia conditions). We identified a total of 821 and 383 metabolites in the gill in positive and negative ion modes, respectively. Of the metabolites identified in positive ion mode, 136 were differentially abundant between hypoxia and all other conditions; of the metabolites identified in negative ion mode, 34 were differentially abundant between hypoxia and all other conditions. The metabolites which were differentially abundant under hypoxia primarily included glycerol phospholipids, fatty acids, hormones, and amino acids as well as related compounds. The pathways which were significantly enriched in the differentially abundant metabolites included the lipid metabolism, amino acid metabolism, purine metabolism, FoxO signaling pathway, and mTOR signaling pathway. Our results help to clarify the mechanisms underlying hypoxia tolerance and to identify hypoxia-related metabolites, as well as to highlight potential research targets for the development of hypoxic-tolerant strains in the future.

Takifugu obscurus has relatively small gills and gill pores, leading to a relatively low respiratory capacity and increased vulnerability to low dissolved oxygen (DO) levels compared to other fish. To investigate the responses of T. obscurus to acute hypoxic stress, high-throughput-sequencing-based transcriptomic analyses were conducted here to assess the responses of T. obscurus gills to acute hypoxic stress. Three environmental conditions were compared including normoxia (DO: 7.0 ± 0.2 mg/L), hypoxic stress (DO: 0.9 ± 0.2 mg/L), and reoxygenation (4, 8, 12, and 24 h after return to normoxia) conditions to identify differentially expressed genes (DEGs) responsive to hypoxia. A total of 992, 877, 1561, 1412, and 679 DEGs were identified in the normoxia and reoxygenation for 4, 8, 12, and 24 h groups in comparison to the hypoxia groups, respectively. The DEGs were primarily associated with oxidative stress, growth and development, and immune responses. Further functional annotation enrichment analysis of the DEGs revealed that they were primarily related to cytokine–cytokine interactions, transforming growth factor β receptor (TGF-β), cell adhesion molecules (CAMs), the vascular endothelial growth factor (VEGF) signaling pathway, and the mitogen-activated protein kinase (MAPK) signaling pathway. These results provide new insights into the physiological and biochemical mechanisms of T. obscurus adaptations to hypoxic stress. Furthermore, these results provide a framework for future studies into the molecular mechanisms of hypoxia tolerance and the healthy culture of T. obscurus and other fish.

The quality of sea urchin gonad is important to consumers with high standards for nutrition and taste. However, few studies have been conductedon the molecular mechanisms that determine the quality of male and female sea urchins. In this study, our goal was to understand the differences and characteristics of gonad quality between sea urchin (Strongylocentrotus intermedius) males and females. The transcriptomes of males and females were obtained, with totals of 43,797,146 and 56,222,782 raw reads, respectively, comprising 128,979 transcripts and 85,745 unigenes. After comparative transcriptome analysis, a total of 6736 differentially expressed genes (DEGs) between the males and females were identified, of which 2950 genes were up-regulated and 3786 genes were down-regulated in males. We compared the expression of twelve DEGs with significant differences their expression levels and functional annotations to confirm the reliability of the RNA-Seq data. Five DEGs related to gonadal quality were found through enrichment analysis of KEGG pathways: 17β-HSD8, PGDH, FAXDC2, C4MO, and PNPLA7. Our study analyzes genes related to the taste and flavor of sea urchin gonads among the sexes and provides reference sequences and fundamental information concerning the nutrition and taste of S. intermedius gonads.

Takifugu rubripes (T. rubripes) is marine fish rich in protein and essential amino acids. With the continuous development of T. rubripes farming, intensive aquaculture has increased the infection rate with fish diseases. To explore the relationship between environmental microbial communities and gut microbiota, we sequenced the 16s rRNA gene V3–V4 region of the microorganisms in the aquaculture water and gut flora of T. rubripes. The results indicated 934 operational taxonomic units for T. rubripes gut contents and aquaculture samples. A total of 31 phyla and 498 genera were identified. At the phylum level, except for the phylum Proteobacteria, the dominant phyla in intestinal contents were Firmicutes, Acidobacteria, and Fusobacteria. However, the dominant phyla in water were Actinobacteria, Cyanobacteria, and Patescibacteria. At the genus level, intestinal contents included Photobacterium, Arcobacter, Vibrio, and Ruminococcaceae. The water samples mainly included Clade_Ia, Rhodobacteraceae, Eutreptiella pomquetensis, Lentibacter, Clade_III, and PeM15. Principal component analysis showed that the microbial compositions of samples from the same source were similar. There were significant differences between the intestinal flora and water microorganisms. Therefore, the research results showed the differences between the microbial communities in the intestinal tract and aquaculture water of T. rubripes and the characteristics of the main pathogenic bacteria; this could help guide the environmental regulation and disease prevention of T. rubripes aquaculture.

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.