Introduction: Deltamethrin is a pyrethroid insecticide commonly used to kill animal parasites in aquaculture. However, increasing evidence suggests that deltamethrin affects the health of aquatic animals by causing tissue damage and even death.Methods: In this study, the damage caused by deltamethrin to the gill and liver tissues, as well as its effects on oxidative stress and immune metabolism, were studied in Paralichthys olivaceus.Results: We observed a positive correlation between the residual levels of deltamethrin (Del) and the exposure concentrations, with the highest residue detected in the 0.28 μg/L concentration group (0.0684 mg/kg at 7 days). Then, we observed different degrees of damage to the gill and liver tissues of the Paralichthys olivaceus, including swelling, apical fusion, shedding of gill secondary lamellae, liver cell necrosis, and nuclear vacuolization, by observing tissue sections. Lysozyme enzyme activity increased, whereas catalase and alkaline phosphatase enzyme activities decreased. The liver transcriptome results of the control and high-concentration (0.28 μg/L) groups showed that there were 697 differentially expressed genes, including 390 upregulated and 307 downregulated genes. These differentially expressed genes were significantly enriched in oxidation-reduction, ferroptosis, steroid biosynthesis, and apoptosis pathways.Discussion: In summary, we found that deltamethrin induces oxidative stress and metabolic disorders in P. olivaceus and leads to inflammation. However, the fish body resists such damage through a complex regulatory network. These experimental results provide a theoretical reference for the safe use of deltamethrin in P. olivaceus.

The cryopreservation and transplantation of germline stem cells (GSCs) have become the key to conserving fish genetic resources and safeguarding species diversity. This study aimed to investigate the effects of post-mortem temperature and time on the preservation of oogonial stem cells (OSCs) in the marine fish Paralichthys olivaceus. OSCs remained viable after fish death, and they remained viable and could be cultured after storage at 19 °C for 15 h and at 4 °C for 24 h. Combined transcriptomic and metabolomic analysis was used to identify the pathways leading to OSC death. Several genes were differentially expressed in the ovarian tissue post-mortem, with the most enriched pathways being ferroptosis, fatty acid metabolism/biosynthesis, glutathione metabolism, citric acid cycle (TCA cycle), and arachidonic acid metabolism signaling pathways. Genes related to ferroptosis, such as vdac2, p53, and slc7a11, as well as metabolites such as adrenic acid and arachidic acid, can serve as reliable biomarkers for evaluating the viability of post-mortem OSCs. These findings provide valuable insights and theoretical support for the effective use of post-mortem GSCs and enhance strategies for germplasm resource conservation in fish.

Artificially induced gynogenesis, a technique that utilizes UV-irradiated sperm to activate eggs while excluding paternal genetic contribution, has been instrumental in the genetic improvement of aquaculture species. Although the allo-sperm effect has been observed in some freshwater fish and suggests the integration of paternal DNA, its occurrence and mechanisms in marine fish remain unclear. In this study, a 795.23 Mb chromosome-level genome assembly for red sea bream (Pagrus major) was presented, with a scaffold N50 of 32.03 Mb, encompassing 29,083 protein-coding genes. Furthermore, the allo-sperm effect was investigated on the artificial gynogenesis of Japanese flounder (Paralichthys olivaceus) induced by UV-irradiated P. major sperm. Whole-genome sequencing of gynogenetic and normal fertilized offspring revealed eight representative genomic sequences with >96.88% nucleotide identity to P. major, including six Sparidae-specific centromeric satellite DNA sequences. PCR validation and Sanger sequencing confirmed that these sequences were present exclusively in gynogenetic groups and absent in normally fertilized offspring, providing direct evidence of the allo-sperm effect. Our findings extend the allo-sperm effect to marine fish and demonstrate its potential across taxonomically distant taxa, P. olivaceus (Pleuronectiformes) × P. major (Spariformes). These results offer valuable genomic information for P. major, and provide important insights for future genetic breeding programs in aquaculture.

Japanese flounder is usually gonochoristic, with gonads that are either testes or ovaries. Here, we report an unusual case of hermaphroditism in Japanese flounder captured from the Bohai Sea. In the intersex flounder, the membrane of the upper ovary was closely connected to the abdominal muscles and internal organs, and the eggs filled the entire abdomen. The lower ovary was small and closely connected to the testes. The testes contained few fully mature sperm. Both eggs and sperm were capable of fertilization. The levels of several reproduction-related hormones (17β-estradiol, 11-ketotestosterone, 17α, 20β-dihydroxyprogesterone, luteinizing hormone, follicle-stimulating hormone, and testosterone) in the intersex flounder were intermediate, between those in females and males. The results showed that the heterozygosity of the intersex flounder was 0.632, and there were 28 single-nucleotide polymorphisms in the cyp21a gene. Compared with that of wild flounder, the activity of 21-hydroxylase was reduced by approximately 20.0%, and expressions of cyp19a, amh, and dmrt1 differed. We present the first report of its kind, detailing the anatomy, hormonal endocrinology, molecular biology, and physiology of the intersex Japanese flounder.