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 obscure puffer (Takifugu obscurus) is a popular cultured species and accounts for around 50% of the total pufferfish production in China. A hybrid puffer was generated by crossing a female obscure puffer with a male tiger puffer (T. rubripes). Its growth model has not been developed and the genetic basis underlying its growth superiority has not yet been fully investigated. In this study, the growth model and morphological traits of the hybrid puffer were explored. The results indicated that the hybrid puffer exhibited a significant growth advantage compared to the obscure puffer. There were also significant differences in their morphological traits. We conducted genotyping-by-sequencing (GBS) on hybrid and obscure puffer groups, identifying 215,288 high-quality single nucleotide polymorphisms (SNPs) on 22 chromosomes. Subsequently, a total of 13 growth-related selection regions were identified via a combination of selection signatures and a genome-wide association study (GWAS); these regions were mainly located on chromosomes 10 and 22. Ultimately, the screened regions contained 13 growth-related genes, including itgav, ighv3-43, ighm, atp6v1b2, pld1, xmrk, inhba, dsp, dsg2, and dsc2, which regulate growth through a variety of pathways. Taken together, the growth models and candidate genes used in this study will aid our understanding of production characteristics and the genetic basis of growth rates. The hybrid will also be of great significance for the genome-assisted breeding of pufferfish in the future.