As aquatic animals, fishes often encounter various situations of low oxygen, and they have evolved the ability to respond to hypoxia stress. Studies of physiological and molecular responses to hypoxia stress are essential to clarify genetic mechanisms underlying hypoxia tolerance in fish. In this study, we performed acute hypoxia treatment in juvenile bighead carp (Hypophthalmicthys nobilis) by decreasing water O₂ from 6.5 mg/L to 0.5 mg/L in three hours. This hypoxia stress resulted in a significant increase in blood lactate and serum glucose. Comparisons of heart transcriptome among hypoxia tolerant (HT), hypoxia sensitive (HS), and normoxia control (NC) groups showed that 820, 273, and 301 differentially expressed genes (DEGs) were identified in HS vs. HT, NC vs. HS, and NC vs. HT (false discovery rate (FDR) < 0.01, Fold Change> 2), respectively. KEGG pathway enrichment showed that DEGs between HS and HT groups were mainly involved in mitogen-activated protein kinase (MAPK) signaling, insulin signaling, apoptosis, tight junction and adrenergic signaling in cardiomyocytes pathways, and DEGs in MAPK signaling pathway played a key role in cardiac tolerance to hypoxia. Combined with the results of our previous cDNA-amplified fragment length polymorphism (cDNA-AFLP) analysis of hypoxia stress in this species, such genes as stbp2, ttn, mapk, kcnh, and tnfrsf were identified in both studies, representing the significance of these DEGs in hypoxia tolerance in bighead carp. These results provide insights into the understanding of genetic modulations for fish heart coping with hypoxia stress and generate basic resources for future breeding studies of hypoxia resistance in bighead carp.

Background: Bighead carp (Hypophthalmichthys nobilis), a vital species in China’s freshwater ecosystems and aquaculture, has experienced significant population declines due to habitat degradation and intensive farming. Methods: In this study, eight polymorphic microsatellite markers were utilized to examine the genotypes and genetic diversity of 320 individuals of bighead carp populations located in the middle Yangtze River. This included four wild populations (ZX, DTH, SS, WH) and six cultured populations (HH, XZ, CH, QC, CD, HG). Results: Wild populations exhibited significantly higher genetic diversity (mean Na = 12.25 ± 0.63, Ho = 0.802 ± 0.063) than cultured groups (mean Na = 8.85 ± 1.21, He = 0.779 ± 0.032). Low differentiation (Fst < 0.05) among wild populations indicated high connectivity with low genetic structure, whereas cultured populations CH and HG showed moderate-to-high differentiation (Fst = 0.156–0.293). Bayesian analysis (K = 7) revealed a distinct clustering of wild populations, while cultured stocks exhibited admixed genetic ancestries. Bottleneck tests confirmed recent genetic bottlenecks in three cultured populations. Conclusions: Wild bighead carp populations retain a critical genetic diversity, serving as reservoirs for conservation, while intensive aquaculture practices threaten genetic integrity through allele loss and inbreeding.

The orbital fat of bighead carp (Hypophthalmichthys nobilis) represents a structural fat deposit located posterior to the eyes and constitutes an important edible component of the head region. Nevertheless, molecular mechanisms governing lipid accumulation during ontogenetic development remain insufficiently characterized. Here, we performed RNA-Seq on orbital fat tissues from 6-month-old (juvenile) and 18-month-old (market-size) bighead carp. A total of 1042 DEGs were identified, with 807 up-regulated and 235 down-regulated in the 6-month-old stage. Functional enrichment revealed key pathways including fatty acid metabolism, PPAR signaling, and glycolysis/gluconeogenesis. qRT-PCR validation confirmed RNA-Seq reliability. Notably, the differential expression patterns of genes such as cpt1a, cpt1b, slc27a1, fads2, and scd suggest their association with an elevated capacity for lipid synthesis in the orbital fat of 18-month-old bighead carp. This study presents the first transcriptome analysis of orbital fat development in a freshwater fish, offering insights into the genetic improvement of head meat quality traits and growth in bighead carp head.

Bighead carp (Hypophthalmichthys nobilis) is a key aquaculture species, with the head and its orbital fat being a commercially valuable product. To elucidate the molecular basis of growth variation, we performed comparative transcriptome analysis of orbital fat from extreme growth phenotypes at juvenile (6 months) and market-size (18 months) stages. In juveniles, slow growth was linked to upregulation of stress-responsive genes (sgk1, fkbp5, lipg), while fast growth correlated with higher expression of stress-buffering (crhbp) and nutrient-signaling (rbp2, mgea5) genes. At 18 months, divergent growth aligned with opposing lipid metabolic states: a pro-anabolic profile (dgat2, fads2) supported fast growth, whereas a catabolic profile (cpt1b, ppargc1a) was associated with slow growth. These results demonstrate stage-specific transcriptional reprogramming in orbital fat underlying growth variation. This study provides a molecular framework for orbital fat-mediated growth regulation and highlights potential candidate genes for molecular breeding in bighead carp.

In April 2025, adult specimens of Diptera were collected in Henan Province, China., and based on an integrated analysis of DNA barcodes and morphology, a new species is formally described as Stictochironomus longtanensis Lei & Zhang, sp. nov . Adult males can be distinguished from all known congeners by a unique combination of morphological traits: a greater hypopygium ratio (1.98–2.11) and longer hypopygium (3.77–4.01), the presence of a white ring on the femur, the wing with a dark spot near the cross vein r-m, and a superior volsella bearing six bristles. Adult females are characterized by a small antennal ratio (AR 0.37–0.39); the wing with a dark spot near the cross vein r-m; genitalia with two ovoid, transparent seminal capsules; and a large, elliptical, densely setose cercus. The average interspecific genetic distance of the new species with congeners substantially exceeds the established threshold for species divergence in Stictochironomus , providing strong molecular evidence supporting this novel species. An updated taxonomic key to the known male adults of Stictochironomus from China is also provided.

(1) Background: Polyploid fish are highly important in increasing fish production, improving fish quality, and breeding new varieties. The loach (Misgurnus anguillicaudatus), as a naturally polyploid fish, serves as an ideal biological model for investigating the mechanisms of chromosome doubling; (2) Methods: In this study, tetraploidization in diploid loach was induced by heat shock treatment, and, for the first time, the role of the key cell cycle gene cdk1 (cyclin-dependent kinase 1) in chromosome doubling was investigated; (3) Results: The experimental results show that when eggs are fertilized for 20 min and then subjected to a 4 min heat shock treatment at 39–40 °C, this represents the optimal induction condition, resulting in a tetraploid rate of 44%. Meanwhile, the results of the cdk1 knockout model (2n cdk1^−/−) constructed using CRISPR/Cas9 showed that the absence of cdk1 significantly increased the chromosome doubling efficiency of the loach. The qPCR analysis revealed that knockout of cdk1 significantly upregulated cyclin genes (ccnb3,ccnc, and ccne1), while inhibiting expression of the separase gene espl1 (p < 0.05); (4) Conclusions: During chromosome doubling in diploid loaches induced by heat shock, knocking out the cdk1 gene can increase the tetraploid induction rate. This effect may occur through downregulation of the espl1 gene. This study offers novel insights into optimizing the induced breeding technology of polyploid fish and deciphering its molecular mechanism, while highlighting the potential application of integrating gene editing with physical induction.