Expression and regulation of Smad2 by gonadotropins in the protogynous hermaphroditic ricefield eel (Monopterus albus).

Smad2, a receptor-activated Smad, plays a critical role in regulating gametogenesis. In this study, a smad2 homologue was identified and sequenced from ricefield eel ovary cDNA, and its mRNA and protein expression levels were analysed during oocyte development. The cDNA sequence of ricefield eel smad2 consisted of 1863 bp encoding a 467-amino acid protein that had high sequence homology with Smad proteins in other teleosts, especially in Poeciliopsis prolifica. The results of real-time quantitative PCR (RT-qPCR) analysis revealed that smad2 is expressed in the ovary during gonad development, increased continuously until the early vitellogenic stage in the ovaries, and then decreased with ovary maturation. Smad2 protein immunoreactivity was localized in the cytoplasm of follicular cells, oogonia, and primary growth stage oocytes. In vitro experiments revealed that follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG) promoted smad2 expression in ovary tissue in a time- and dose-dependent manner, respectively. In summary, Smad2 plays a potentially vital role in ricefield eel ovary development.

Effects of different temperatures on Leiocassis longirostris gill structure and intestinal microbial composition.

Fish are poikilothermic vertebrates and their physiological activities are affected by water temperature. In recent years, extreme weather has occurred frequently, and temperature changes have adversely affected the growth of farmed fish. To explore the changes in gill tissue structure caused by changing the water temperature and the relationship between the intestinal microbiota and the Leiocassis longirostris host adaptation mechanism, gill tissue sections and intestinal microbial 16S rRNA amplicon sequencing were conducted under different temperature stress (low temperature 4 °C, normal temperature 26 °C and high temperature 32 °C). The results showed that heat stress and cold stress caused injury and swelling, terminal congestion, cell vacuolation, and necrosis of the gill tissue of L. longirostris. For intestinal microbiota, the abundances of Pseudomonadota and Bacillota increased at the cold stress, while the abundances of Fusobacteriota and Bacteroidota increased at the heat stress. The number of opportunistic bacteria, mainly Aeromonas and Acinetobacter, was the highest under cold stress. In addition, the richness of the intestinal microbiota decreased significantly at heat and cold stresses, while evenness increased. Prediction of intestinal microbiota function showed that most common functions, such as metabolism of cofactors and vitamins, energy metabolism and replication and repair, were decreased significantly at heat stress and cold stress, and phylogenetic relationship analysis revealed significant differences among the groups. In conclusion, the change of temperature altered the gill tissue structure, and affected the structure and homeostasis of the intestinal microbiota, thus affecting the survival time of L. longirostris, and cold stress had a greater effect than heat stress.

Integrated analysis of how gender and body weight affect the intestinal microbial diversity of Gymnocypris chilianensis.

Intestinal microorganisms that living in the mucosa and contents of the gastrointestinal tract of animals, have close links with their hosts over a long evolutionary history. The community structure of the fish intestinal microbiota is associated with food, living environment, and the growth stage. To screen for potential probiotics that can be used for regulating breeding behaviors, this study focused on the diversity of fish intestinal microorganisms. This study aimed to investigate the effects of sex and body weight on the intestinal microbial diversity of Gymnocypris chilianensis in the wild. The results showed that the significant high diversity and richness of intestinal microbiota were fould in heavier individuals, and males. The dominant bacterial phyla of G. chilianensis were Proteobacteria, Firmicutes, and Bacteroidetes. In addition, the abundance of Firmicutes varied significantly among different body weights. The genus profile revealed that small individuals were dominated by Weissella, while females were dominated by Aeromonas, and both large individuals and males were dominated by other genera. Phylogenetic relationships and UPGMA clustering analysis showed significant differences among the groups. In general, the two main factors that have an effect on the intestinal microbiota diversity of wild G. chilianensis are sex and body weight.

Genetic analysis of wild Ancherythroculter nigrocauda in tributaries and the main stream of the upper Yangtze River basin of China.

Biodiversity is threatened by several factors that are often associated with overfishing, water pollution and hydroelectric dams, among other environmental impacts. The present study aimed to evaluate the genetic aspects of wild groups of Ancherythroculter nigrocauda using the mitochondrial cytochrome c oxidase subunit I (coI) and cytochrome b (cytb) genes and the d-loop region. We collected 89 representative individuals from three geographically distinct ranges of the Upper Yangtze River, including the Longxi River (LOR), Laixi River (LAR), and Hejiang range of the Yangtze River (HJ). The genetic analysis results showed that the three populations of A. nigrocauda had high levels of haplotype diversity (0.3434-0.951) and low levels of nucleotide diversity (0.00074-0.00412) based on the single gene sequences and the combination of gene sequences. Haplotype genealogy showed that only one haplotype (Hap-2) was shared by these three geographic groups, and 2-3 were shared by two groups; the other haplotypes were group-specific. The genetic distance within and between the populations was low; however, most of the molecular variance came from within the populations. Furthermore, high gene flow (>1.0) was found in HJ vs LOR and HJ vs LAR based on the d-loop region sequence and combination. These results suggested that there was a decrease in the degree of A. nigrocauda genetic diversity in the upper Yangtze River, and the genetic protection of the populations should be highlighted in the future.

Characterization and expression profiles of cyp19a1a in the schizothoracine fish Schizothorax prenanti.

Aromatase plays a central role in ovarian differentiation and development in teleosts. In the present study, we identified a cyp19a1a homologue from the ovary of Schizothorax prenanti and analysed its expression at both the mRNA and protein levels. Cyp19a1a of S. prenanti showed high homology with that of other teleosts, especially S. kozlovi. The ovary and testis were the main sites of cyp19a1a expression in S. prenanti, and cyp19a1a transcript levels peaked in the mid-vitellogenic (MVG)-stage ovary and the mid-spermatogenic (MS)-stage testis. Signals of Cyp19a1a immunopositivity were detected in the spermatocytes and follicular cells of cortical alveolar-stage and MVG oocytes but not in spermatogonia or spermatids. Taken together, these findings indicate that Cyp19a1a may play an important role in oocyte vitellogenesis as well as spermatocyte development in S. prenanti.

The complete mitochondrial DNA of Ancherythroculter wangi.

The complete mitochondrial genome of Ancherythroculter wangi was determined. The mitochondrial genome, consisting of 16,622 base pairs (bp), encoded 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a non-coding control region, as those found in other Ancherythroculter species. These results can provide useful data for further studies on taxonomic status, molecular systematics, and stock evaluation.

The complete mitochondrial DNA of Gymnocypris potanini firmispinatus and comparative mitogenomic analyses of the Gymnocypris species.

The complete mitochondrial genome of Gymnocypris potanini firmispinatus was sequenced and compared with others Gymnocypris species. The mitochondrial genome, consisting of 16,680 base pairs (bp), encoded 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a non-coding control region, as those found in other Gymnocypris species. These results can provide useful data for further studies on taxonomic status, molecular systematics and stock evaluation.

The complete mitochondrial DNA of Gymnocypris potanini Herzensten and comparative mitogenomic analyses in Gymnocypris species.

In the study, the complete mitochondrial genome of Gymnocypris potanini Herzensten was sequenced and compared with other Gymnocypris species. The mitochondrial genome, consisting of 16,749 base pairs (bp), encoded 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a noncoding control region, similar as that found in other Gymnocypris species. These results can provide useful information for further studies on taxonomic status, molecular systematics, and stock evaluation.