Hypoxia stress alters gene expression in the gills and spleen of greater amberjack (Serioladumerili).

Greater amberjack (Seriola dumerili) is a fish species that has significant economic and cultural value. It has a large size and grows rapidly. However, the intolerance to hypoxia poses a major obstacle to the growth of its aquaculture industry. This study focuses on the gills and spleen, two organs closely associated with the response to acute hypoxic stress. By simulating the acute hypoxic environment and using Illumina RNA-Seq technology, we explored the gills and spleen transcriptome changes in the acute hypoxia intolerant and tolerant groups of greater amberjack. It was discovered that gill tissues in the tolerant group may maintain a stable intracellular energy supply by promoting glycolysis and ß-oxidation compared to the intolerant group. Additionally, it promotes angiogenesis, enhances the ability to absorb dissolved oxygen, and accelerates oxygen transport to the mitochondria, adapting to the hypoxic environment. Anti-apoptotic genes were up-regulated in gill tissues in the tolerant group compared to the intolerant group, thereby minimizing the damage of acute hypoxia. On the other hand, the spleen inhibited the TCA and energy-consuming lipid synthesis pathways to supply energy under acute hypoxic stress. Pro-angiogenic genes were down-regulated in the spleen of individuals in the tolerant group compared to the intolerant group, which may be related to organ function. The suppressed reactive oxygen species (ROS) production and the impaired immune response function of the spleen were also found. The study explored the acute hypoxic stress response in greater amberjack and the molecular mechanisms underlying its tolerance to acute hypoxia.

Addition of Cryoprotectant DMSO Reduces Damage to Spermatozoa of Yellow Catfish (Pelteobagrus fulvidraco) during Cryopreservation: Ultrastructural Damage, Oxidative Damage and DNA Damage.

Spermatozoa cryopreservation protocols have been established for yellow catfish (Pelteobagrus fulvidraco), but cryopreservation can still cause cellular damage and affect spermatozoa viability and fertility. Therefore, the aim of this paper was to evaluate the effects of adding or not adding cryoprotectants during low-temperature storage on the ultrastructural damage, oxidative damage, and DNA damage of thawed yellow catfish spermatozoa. The mixed semen of three male yellow catfish was divided into a fresh spermatozoa group, a frozen spermatozoa group (DMSO+) with a cryoprotectant (10% DMSO), and a frozen spermatozoa group without a cryoprotectant (DMSO-). Ultrastructural of the spermatozoa after thawing were observed under an electron microscope and the spermatozoa were assayed for SOD, MDA, and T-AOC enzyme activities, as well as for DNA integrity. In terms of movement parameters, compared with DMSO-, the addition of DMSO has significantly improved sperm motility, curve line velocity (VCL), and straight line velocity (VSL). The ultrastructural results showed that although thawed spermatozoa exhibited increased damage than fresh spermatozoa, 10% DMSO effectively reduced the damage to the plasma membrane, mitochondria, and flagellum of spermatozoa by cryopreservation, and most of the spermatozoa were preserved with intact structure. The results of oxidative damage showed that compared with frozen spermatozoa, 10% DMSO significantly increased the activities of SOD and T-AOC enzymes and clearly reduced the activity of the MDA enzyme. The antioxidant capacity of spermatozoa was improved, lipid peroxidation was reduced, and the oxidative damage caused by cryopreservation was mitigated. The DNA integrity of spermatozoa showed that 10% DMSO clearly reduced the DNA fragmentation rate. In conclusion, 10% DMSO can effectively reduce the ultrastructural damage, oxidative damage, and DNA damage of yellow catfish spermatozoa during cryopreservation; it can also further optimize the cryopreservation protocol for yellow catfish spermatozoa. Meanwhile, it also provides a theoretical basis for the future optimization of the cryopreservation protocols.

Chromosome-level genome assembly and annotation of the yellow grouper, Epinephelus awoara.

Epinephelus awoara, as known as yellow grouper, is a significant economic marine fish that has been bred artificially in China. However, the genetic structure and evolutionary history of yellow grouper remains largely unknown. Here, this work presents the high-quality chromosome-level genome assembly of yellow grouper using PacBio single molecule sequencing technique (SMRT) and High-through chromosome conformation capture (Hi-C) technologies. The 984.48 Mb chromosome-level genome of yellow grouper was assembled, with a contig N50 length of 39.77 Mb and scaffold N50 length of 41.39 Mb. Approximately 99.76% of assembled sequences were anchored into 24 pseudo-chromosomes with the assistance of Hi-C reads. Furthermore, approximately 41.17% of the genome was composed of repetitive elements. In total, 24,541 protein-coding genes were predicted, of which 22,509 (91.72%) genes were functionally annotated. The highly accurate, chromosome-level reference genome assembly and annotation are crucial to the understanding of population genetic structure, adaptive evolution and speciation of the yellow grouper.

Supplementation of Extender with Melatonin Improves the Motility, Mitochondrial Membrane Potential, and Fertilization Ability of Cryopreserved Brown-Marbled Grouper Sperm.

Sperm cryopreservation is a valuable tool for breeding, conservation, and genetic improvement in aquatic resources, while oxidative damage will cause a decline in sperm quality during this progress. Melatonin (MT), a natural antioxidant hormone, is used as an additive in sperm cryopreservation to reduce cellular damage from oxidative stress. Here, we aimed to investigate the effect of adding MT to the freezing medium in sperm cryopreservation of brown-marbled grouper (Epinephelus fuscoguttatus). Different concentrations of MT (0, 0.1, 0.25, and 0.5 mg/mL) were tested. We evaluated sperm motility, viability, apoptosis, mitochondrial membrane potential (MMP), and fertilization ability to assess the effects of MT supplementation. Our results demonstrated that the addition of MT to the extender improved the post-thaw motility, MMP, and fertilization ability of brown-marbled grouper sperm. The total motility, curvilinear velocity, straight linear velocity, and average path velocity in MT-treated groups (0.1 and 0.25 mg/mL) exhibited significantly higher values than that of the control group. A higher MMP (p < 0.05) was observed in the group treated with 0.25 mg/mL MT, suggesting that supplementation of MT in the extender might be able to protect mitochondrial membrane integrity effectively. Regarding fertilizing ability, 0.25 mg/mL MT yielded a significantly higher hatching rate than the control. An adverse effect was found with the concentration of MT up to 0.5 mg/mL, suggesting the possible toxicity of a high-dose addition. In this study, we optimized the sperm cryopreservation protocol of brown-marbled grouper, which might be valuable for sperm cryopreservation and sample commercialization of groupers and other fish.

Liver Transcriptome Shows Differences between Acute Hypoxia-Tolerant and Intolerant Individuals of Greater Amberjack (Seriola dumerili).

Acute hypoxia is a common abiotic stress in commercial aquaculture and has significant effects on fish physiology and metabolism. Due to its large size and rapid growth, the greater amberjack (Seriola dumerili) is an economically important fish with high farming value. This species is intolerant to hypoxia, which makes it susceptible to mass mortality and hinders the progress of amberjack cultivation. Based on a comparative analysis of the liver transcriptome between acute hypoxia-tolerant (HT) and -intolerant (HS) groups, this study first explored the molecular mechanisms of acute hypoxia in greater amberjack. By simulating the acute hypoxic environment and using RNA sequencing (RNA-Seq), the differences in liver transcriptional changes between the acute hypoxia-tolerant (HT) and hypoxia-intolerant (HS) groups of greater amberjack were probed. Based on differential expression analysis, 829 differentially expressed genes (DEGs) were screened in both groups. Relative to the HS group, 374 DEGs were upregulated and 455 were downregulated in the HT group. Compared with the HS group, genes such as slc2a5 and prkaa2 related to promoting sugar transport and inhibiting lipid syntheses were upregulated, while genes that inhibit gluconeogenesis and promote lipid syntheses, such as pgp and aacs, were downregulated. The expression of odc1 was significantly and relatively downregulated in the HT group, which would lead to the inhibition of intracellular antioxidant activity and decreased scavenging of ROS. The NF-kB pathway was also promoted to some extent in individuals in the HT group relative to the HS group to resist apoptosis. In addition, the relative downregulation of apoptosis and autophagy-related genes, such as endog, hm13, and casp6, was also detected in the HT group. The present findings first reported the regulation mechanism by which liver tissue coped with the acute hypoxia stress in greater amberjack, which will provide important technical support for preventing acute hypoxia-induced death in advance and reducing economic losses.