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Hypoxia has become a common phenomenon in aquatic environments. Golden pompano (Trachinotus blochii) are sensitive to fluctuations in dissolved oxygen concentration and are seriously affected by hypoxic stress. When facing hypoxia in aquaculture areas, it may be effective to alleviate the adverse effects of low oxygen by increasing dissolved oxygen through physical and chemical means. However, it is not known whether different reoxygenation rates have different physiological consequences. In this study, we utilized RNA-seq and miRNA-seq to investigate the effects of various hypoxia and reoxygenation treatments: normoxia, hypoxia, rapid reoxygenation (RRG; dissolved oxygen [DO] recovery within 10 mins), and gradual reoxygenation (GRG; DO recovery within 3 h). Under hypoxic conditions, the miR-130b-5p∼IDH3 pair was involved in the regulation of the TCA cycle and activation of HIF-1α expression in response to insufficient oxygen levels. Additionally, in RRG, under the regulation of the miR-132–5p∼PGAM, miR-8485∼LIPA, and miR-212–5p∼GAPDHS pairs, the energy supply came to increase relative to hypoxia. In GRG, the miR-130b-5p∼IDH3 pair regulated metabolism, which returned to the normal level. These findings provide new data for clarifying the metabolic regulatory pathways of golden pompano during hypoxia and reoxygenation processes.

The fluctuations of dissolved oxygen (DO) often lead to hypoxia in aquaculture, which has a huge adverse impact on fish. This study mainly investigated the effects of long-term hypoxia on oxidative stress, immune response, and cell apoptosis in the liver of golden pompano (Trachinotus blochii), which is not tolerant to hypoxia. So we conducted a 14 day low oxygen stress experiment on the golden pompano with a DO of 3.0 ± 0.2 mg/L, then restore the DO to normal levels and continue the 14 day reoxygenation experiment. Results showed that hypoxia and reoxygenation led to significant changes in liver structure. During hypoxia and reoxygenation, the expression of oxidative stress related genes (SOD1, SOD2, GSH-Px, and CAT) and levels of antioxidant enzymes (CAT and MDA) in the liver were increased. Liver lysozyme activity and the relative expression of the pro-inflammatory factors interleukin (IL)-1β were significantly increased, but the expression of IL-34 was down-regulated during hypoxia. The expression of IL-12β was significantly increased during reoxygenation. The expression of anti-inflammatory factor IL-11 was decreased duringreoxygenation. The expression of toll like receptors (TLRs) -7, -8, and -9 increases after hypoxia and decreases after reoxygenation, indicating that both hypoxia and reoxygenation affect the immune response. In addition, during hypoxia and reoxygenation, TUNEL-positive signals increased, the bcl2/bax ratio decreased, the expression levels of caspases-3 and -8 were significantly up-regulated during hypoxia, and expression levels of caspases-9 was up-regulated during reoxygenation. In summary, hypoxia and reoxygenation can cause oxidative stress, induce inflammatory reactions, inhibit immune processes, activate apoptosis, and lead to liver damage of the golden pompano, which may be irreversible.

Globally, microplastics (MPs) are highly prevalent, especially in coastal areas. Unfortunately, golden pompano as a major marine fish in China is typically raised in floating marine cages near coasts, facing these MPs sources. However, toxicological studies on Golden Pompano which farm in coastal areas and face actual microplastic exposure are rare. Therefore, golden pompano were exposed to 10.0 μg/L, 100.0 μg/L, and 1000.0 μg/L polystyrene MPs (PS-MPs) for 14 days to study the potential impact of the microplastics on the Golden Pompano. Fish show slowed growth after 14 days of exposure. Histopathology shows irregular shaped nuclei and nuclear and cytoplasmic vacuolation traits in liver. Oxidative stress-related enzyme activity and gene expression data show that oxidative damage occurs in the high-concentrations (100.0 μg/L and 1000.0 μg/L) of PS-MPs exposures. Up-regulation of Grp78, Xbp-1, Eif-2α and chop gene expression indicates the occurrence of endoplasmic reticulum stress, and the western blot results also confirmed this. Severe oxidative stress also caused ERS, which ultimately increased BAX/Bcl-2 ratios and induces apoptosis. Furthermore, up-regulated anaerobic respiration, altered lipid metabolism, and immune disturbance were exhibited during PS-MPs stress. Therefore, oxidative stress appeared to be the main toxicity issue caused by MPs, while ERS-mediated apoptosis, metabolic alterations, and immune responses were induced by this stress. Notably, endoplasmic reticulum stress and apoptosis are a self-protective mechanism, which may be an intermediate link in the toxicity of microplastics. This study highlights the role of endoplasmic reticulum stress in MPs toxicology and assesses the adverse effects of microplastics on Golden Pompano.

Golden pompano (Trachinotus blochii) is becoming increasingly popular and produces high yields, but the growth differences between males and females are a concern. In this study, the differences between the growth of males and females were compared, and the transcriptome analysis of muscle tissues was performed. A significant difference between the growth of males and females was observed; females were found to be 17% larger than males after reaching 7 months of age. Gonadal histological analysis revealed that the ovaries were arrested in 7- to 9-month-old golden pompano, whereas the testes continued to develop. The AMPK and adipocytokine signaling pathways were also found to be involved in the regulation of muscle growth and metabolism. After reaching 7 months of age, the expression levels of glut1, glut4, ldh, gys, acsl and cpt2 in the muscle of females were lower than those in males, but the hk gene, which is involved in glycolysis, was found to remain highly expressed in females. Additionally, in females, the synthesis of arginine and ornithine and the production of carnosine were found to be inhibited, but the breakdown of glutamine was found to be enhanced and OXPHOS ability was found to be stronger in females after reaching 7 months of age. These results support a certain negative correlation between gonadal development and muscle metabolism depending on differences in energy distribution. Clearly, the faster growth in females after reaching 7 months of age was found to be associated with the more active metabolism of glucose, and amino acids, as well as stronger oxidative phosphorylation levels.