This study presents the first complete mitochondrial genome characterization of Elops machnata (Teleostei: Elopiformes: Elopidae), a basal teleost lineage critical for understanding early actinopterygian evolution. The assembled mitogenome, deposited under GenBank accession number PV294982, spans 16,712 bp and exhibits the canonical vertebrate mitochondrial gene organization, comprising 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region. Base composition analysis revealed 22.71% A, 17.36% C, 29.82% T, and 30.11% G, with a slight AT bias (A + T = 52.53%). Codon usage analysis of the 13 protein-coding genes identified CUA (L), CGA (R), GCC (A), and GGA (G) as the most frequent codons, with a pronounced preference for adenine at the third codon position. Amino acid composition analysis across 23 Elopomorpha species revealed consistently high leucine contents, and tRNA secondary structure prediction showed 21 tRNAs forming typical cloverleaf structures, except for trnS1(gct), which lacks the dihydrouridine (DHU) arm. Phylogenetic reconstruction using maximum likelihood and Bayesian inference methods, based on concatenated mitochondrial protein-coding genes from 23 Elopomorpha species, placed E. machnata in a well-supported clade with Elops hawaiensis, confirming their close evolutionary relationship. This study not only provides essential genomic resources for E. machnata but also resolves key gaps in the mitochondrial genome and improves phylogenetic understanding of Elopomorpha.

The rice field eel (Monopterus albus) undergoes natural protogynous sex reversal, but whether peripheral sensory tissues differ across sexual stages remains poorly understood. We used single-nucleus RNA sequencing to characterize the olfactory epithelium (OE) of female, intersex, and male rice field eels. After quality control, 22,959 nuclei were retained and classified into 19 cell populations, including olfactory sensory neurons (OSNs), basal/progenitor, epithelial, mesenchymal, endothelial, and immune populations. OE tissues from five individuals within each sexual stage were pooled prior to nuclei isolation, resulting in one pooled snRNA-Seq library per stage; therefore, between-stage comparisons are interpreted as exploratory and descriptive rather than as independently replicated population-level differences. The relative representation of captured nuclei differed among stages, particularly within the sensory neuronal and basal-cell compartments. Pseudotime analysis placed immature OSNs at relatively early transcriptional states associated with ciliated and microvillous OSN populations, whereas CrOSNs were not continuously connected to the principal iOSN–cOSN/mOSN trajectory. Cell-type-specific analyses identified stage-associated transcriptional differences in basal cells and multiple OSN populations. Predicted cell–cell communication profiles also differed among stages, with male OE showing a larger nominal number of inferred interactions but lower overall predicted interaction strength. Expression patterns of ompa, gng8, and ora4 supported the marker-based annotation of major OSN populations within the dataset. These findings provide an exploratory single-nucleus framework for investigating stage-associated variation in the peripheral olfactory system of M. albus.

Fish show exceptional diversity in sex-determination mechanisms, making them a powerful system for studying how these pathways evolve. However, no definitive master sex-determining gene has yet been identified in Cyprinidae, a widely distributed and species-rich fish family. Here, we identified a male-specific gene in common carp encoding Pangu, a helix-loop-helix (HLH) domain peptide localized to Sertoli cells. Loss- and gain-of-function analyses demonstrate that pangu is both necessary and sufficient for male sex determination. Expression and reporter assays indicate that pangu represses cyp19a1a , a key regulator of ovarian differentiation, and disruption of cyp19a1a restores testicular development in the feminized phenotype of XY pangu mutants. These findings establish pangu as the master sex-determining gene in common carp and link an HLH domain peptide to sex differentiation.

We examined basal and exposure-associated transcript abundance in Pacific abalone. Pi3k, Akt, mTOR, Hsf1, Hsp70, and Hsp90 were compared across five anatomical samples and between heat-selected and common populations after identical two-week acclimation. Five transcripts were examined during adult exposure to 30 °C for up to 72 h and after a 15 min larval heat shock. Basal groups had three animal samples; population and adult groups had two or three analyzed samples. Larval groups comprised three pools of 500 individuals. Qualitative histology used three animals per condition. Welch tests on log2 values used Holm correction. Selected animals had higher hepatopancreatic Pi3k, Akt, mTOR, and Hsp70 levels. Hepatopancreatic Hsf1/Hsp70 means were highest at 12 h and Pi3k/Akt means at 24 h; peak times were not statistically compared. All five transcripts increased within late-veliger samples, without establishing a stage-by-treatment interaction. Histology showed local discontinuities, including in controls. These patterns identify candidate transcript-level indicators. One adult tank per condition, absent time-matched control comparisons, unverified larval culture independence, small samples, normalization uncertainty, population-history confounding, and absent protein endpoints and direct tolerance measurements limit interpretation.