Clostridium butyricum, recognized as a probiotic, is widely distributed in the intestines of various animals. In this study, the C. butyricum strain YF1 was isolated from the intestine of the ricefield eel (Monopterus albus) using an anaerobic culture method and was identified through morphological, physiological, biochemical, and 16S rRNA sequence analyses. Notably, C. butyricum YF1 exhibited a rapid growth rate and was found to produce ten types of short-chain fatty acids, particularly high-yield acetic acid and butyric acid. Additionally, YF1 demonstrated a high tolerance to elevated temperatures (70 °C), bile salts (0.1% to 0.5%), artificial intestinal fluid, and artificial gastric fluid, while being sensitive to most antibiotics. Further whole-genome sequencing revealed that C. butyricum YF1 has a total genome size of 4,314,266 bp and contains 3853 coding genes. Specifically, 82 tRNAs, 21 rRNAs, 288 repeat sequences, 13 prophages, and two gene islands were detected. Moreover, gene function analysis indicated that the highest number of genes were annotated to metabolic processes, and the butyric acid metabolism pathway was found to be complete. Meanwhile, 598 virulence genes and 186 resistance genes were predicted. In conclusion, the findings from this study contribute to probiotic development and provide innovative approaches for the sustainable and healthy cultivation of ricefield eels.

Brachymystax tsinlingensis Li is an endangered cold-water salmonid fish native to China. This study aimed to identify sex-related genes and biological pathways via gonadal transcriptome sequencing of B. tsinlingensis Li. A total of 167,904 unigenes were identified with an average length of 836 bp and an N50 of 1452 bp, of which 84,977 (50.61%) unigenes were successfully annotated in six major databases. Comparative transcriptome analysis identified 22,864 differentially expressed genes (DEGs), of which 17,231 were up-regulated (male-biased genes, mDEGs) and 5633 were down-regulated (female-biased genes, fDEGs). Several DEGs associated with gonadal development were found through Gene Ontology enrichment analysis, such as ccnb1, zp3, bmp15, dmrt1, and psmc3ip. Signaling pathways related to gonadal development were found to be enriched through analysis using the Kyoto Encyclopedia of Genes and Genomes Pathway database, such as genes involves in base excision repair, the notch signaling pathway, neuroactive ligand-receptor interaction, the VEGF signaling pathway, and the estrogen signaling pathway. In addition, mRNA expression levels of 19 DEGs were determined to validate the reliability of the transcriptomic data by quantitative real-time polymerase chain reaction. These results revealed genes and signaling pathways potentially involved in gonadal development in B. tsinlingensis Li and provided basic molecular data for future research on reproductive regulation and breeding of B. tsinlingensis Li.

The largefin longbarbel catfish (Hemibagrus macropterus), a freshwater species endemic to China with fundamental economic importance, requires investigation into its genetic structure for effective management. In this study, we employed mitochondrial cytochrome b (Cytb) gene sequences and 14 microsatellite loci to elucidate the genetic structure of 195 individuals across eight distinct populations. The Cytb analysis revealed a haplotype number (H) of 31, haplotype diversity (Hd) of 0.853, and nucleotide diversity (π) of 0.0127. Population neutrality tests indicated that Tajima’s D (−0.59467) and Fu and Li’s D* (0.56621) were not statistically significant, and the mismatch distribution exhibited a multimodal pattern. Microsatellite analysis revealed that the mean number of alleles (Na), observed heterozygosity (Ho), and polymorphic information content (PIC) across all loci were 18.500, 0.761, and 0.808, respectively. The UPGMA phylogram constructed based on genetic distance identified two distinct clusters, with paired Fst values ranging from 0.108 to 0.138. These results suggest that the largefin longbarbel catfish is in a state of dynamic equilibrium with high genetic diversity. Furthermore, there was significant genetic differentiation between the YB population and the other seven populations, indicating that the population in the upper reaches of the Yangtze River should be managed as a distinct unit.