Freshwater scarcity makes saline–alkaline water essential for sustainable aquaculture. Current research has primarily focused on individual salinity or alkalinity effects on fish, with limited studies addressing their interactive effects. We found significant synergistic toxicity between salinity and alkalinity (r ≈ −0.950/−0.925) in largemouth bass (Micropterus salmoides), demonstrating higher salinity levels corresponding to lower 96-h median lethal concentration (96 h LC₅₀) values for alkalinity, and vice versa. A subsequent 56-day subacute stress trial (salinity: 6‰; alkalinity: 20 mmol/L) assessed the impact on largemouth bass through growth efficiency, histopathology, biochemical assays, transcriptomics, and metabolomics, comparing a saline–alkaline group (SA) with a normal control group (NC). There were no significant differences in growth or survival between the SA and NC groups, but the SA group exhibited pathological changes in gill and liver tissues. Biochemically, the SA group exhibited elevated malondialdehyde, glutathione, and blood urea nitrogen levels, whereas glutathione peroxidase activity significantly decreased. Integrated transcriptomics and metabolomics analyses demonstrated that saline–alkaline stress disrupts lipid, amino acid, and steroid metabolism in largemouth bass, affecting steroid biosynthesis, fatty acid metabolism, glycerophospholipid metabolism, and cysteine and methionine metabolism pathways. Fish adapt by adjusting gene expression and metabolite levels to maintain metabolic balance. This study highlights adaptive mechanisms and applications for sustainable largemouth bass culture in saline–alkaline environments.

The roughskin sculpin (Trachidermus fasciatus) is an endangered fish species in China. In recent years, artificial breeding technology has made significant progress, and the population of roughskin sculpin has recovered in the natural environment through enhancement programs and the release of juveniles. However, the effects of released roughskin sculpin on the genetic structure and diversity of wild populations remain unclear. Studies on genetic diversity analysis based on different types and numbers of molecular markers have yielded inconsistent results. In this study, we obtained 2,610,157 high-quality SNPs and 494,698 InDels through whole-genome resequencing of two farmed populations and one wild population. Both farmed populations showed consistent levels of genomic polymorphism and a slight increase in linkage compared with wild populations. The population structure of the two farmed populations was distinct from that of the wild population, but the degree of genetic differentiation was low (overall average Fst = 0.015). Selective sweep analysis showed that 523,529 genes were selected in the two farmed populations, and KEGG enrichment analysis showed that the selected genes were related to amino acid metabolism, which might be caused by artificial feeding. The findings of this study provide valuable additions to the existing genomic resources to help conserve roughskin sculpin populations.

Fish germline stem cells (GSCs) are pivotal mediators in the transmission of genetic information across generations, possessing irreplaceable significance in aquatic germplasm protection and genetic breeding. Stable in vitro culture serves as an essential prerequisite for construction of standardized fish GSC germplasm repositories. Only by developing a robust culture system to sustain long-term proliferation and stemness of GSCs can large-scale cell reserves be established and long-term safe preservation be realized, and relevant applications including germ cell transplantation (GCT), in vitro differentiation and gene editing be further supported. However, most existing studies focus merely on individual techniques or partial research modules, while few integrate GSC biological mechanisms, in vitro culture systems, and germplasm repository construction with downstream industrial applications. This review elaborates the biological characteristics and classification of fish GSCs, summarizes the regulatory mechanisms of GSC fate determination, and comprehensively updates the research progress of in vitro culture technology and germplasm repository development. Multiple application scenarios based on cell bank resources are holistically illustrated, and prevailing technical and industrial challenges are analyzed. The study aims to provide theoretical reference for promoting technological innovation and practical utilization of fish germ stem cell research.

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.