The mud snail Cipangopaludina cathayensis is a widely distributed species in China. Particularly in Guangxi province, mud snail farming contributes significantly to the economic development. However, global warming in recent decades poses a serious threat to global aquaculture production. The rising water temperature is harmful to aquatic animals. The present study explored the effects of high temperature on the intestinal microbiota of C. cathayensis. Snail intestinal samples were collected from the control and high-temperature groups on days 3 and 7 to determine the gut microbiota composition and diversity. Gut bacterial community composition was investigated using high-throughput sequencing of the V3–V4 region of bacterial 16S rRNA genes. Our results suggested that thermal stress altered the gut microbiome structure of C. cathayensis. At the phylum level, Proteobacteria, Bacteroidetes, and Firmicutes were dominant in C. cathayensis gut microbiota. The T2 treatment (32 ± 1 °C, day 7) significantly decreased the relative abundance of Firmicutes, Actinobacteria, and Deinococcus-Thermus. In T2, the abundance of several genera of putatively beneficial bacteria (Pseudomonas, Aeromonas, Rhodobacter, and Bacteroides) decreased, whereas the abundance of Halomonas—a pathogenic bacterial genus—increased. The functional prediction results indicated that T2 treatment inhibited some carbohydrate metabolism pathways and induced certain disease-related pathways (e.g., those related to systemic lupus erythematosus, Vibrio cholerae infection, hypertrophic cardiomyopathy, and shigellosis). Thus, high temperature profoundly affected the community structure and function of C. cathayensis gut microbiota. The results provide insights into the mechanisms associated with response of C. cathayensis intestinal microbiota to global warming.

Angulyagra polyzonata is an economically important mollusk in China, but detailed insights into its mitochondrial genome remain scarce. In this study, we sequenced and comprehensively analyzed the structural features and selection pressures of the A. polyzonata mitochondrial genome. The maximum likelihood method and Bayesian phylogenetic inference method were used to construct a phylogenetic tree of A. polyzonata with 21 other species, including gastropods and bivalves. The full-length mitochondrial genome of 17,379 bp was found to include 22 transfer RNA genes, 2 ribosomal RNA genes, and 13 protein-coding genes, exhibiting similarity to the composition and arrangement of mitochondrial genes in other gastropod species. Notably, the Ka/Ks ratios of mitochondrial protein-coding genes (nad5, cox3, nad3, nad2, cox1, cox2, atp8, atp6, nadl, nad6, cob, nad4l, and nad4) were <1, which indicates that the snail genes of the three genera of the family may have been subjected to strong natural selection pressure during the evolutionary process, so that the number of synonymous mutations (ks) in genes was much more than that of nonsynonymous mutations (ka). Comparative genomic analysis indicated that, apart from the absence of trnW and trnQ, the gene composition of A. polyzonata shares a high degree of homology with other members of the conical snail family. Phylogenetic analysis demonstrated that the selected species could be classified into two primary clades in which A. polyzonata clustered with the Viviparidae family. This study bridges the knowledge gap regarding the mitochondrial genome of A. polyzonata and offers valuable insights into the systematic relationships within the Viviparidae family.

Angulyagra polyzonata is a significant freshwater snail species in southern China. However, its wild resources have sharply declined due to overfishing. To assess the current status of germplasm resources in the Guangxi region, during this study, we first successfully developed nine pairs of primers that enable the amplification of highly polymorphic microsatellite markers (SSRs) with trinucleotide and tetranucleotide repeat sequences (PIC values ranging from 0.662 to 0.861) using transcriptomic data. Then, these designed primers were tested and applied for the genetic investigation of selected wild populations of the species. Finally, a genetic diversity analysis was conducted based on 12 wild populations (360 individuals) in Guangxi. After 798,244 SSR loci were screened out via high-throughput sequencing, the results showed that dinucleotide repeats accounted for the highest proportion (47.64%), mainly consisting of (AC/GT)n repeat units. Among the SSR loci in A. polyzonata, microsatellite loci with 5 to 20+ repeats are the most abundant. All nine selected and tested SSR loci significantly deviated from Hardy–Weinberg equilibrium (p < 0.001) and had heterozygote deficiency (average inbreeding coefficient of F = 0.390), indicating widespread inbreeding. The fixation index among populations was high (average Fst = 0.175), with 73% of the genetic variation occurring within populations and 27% between populations. Gene flow (Nm) was generally restricted (most population pairs had Nm < 1), with the (Tiandeng) TD and (Long’an) LA populations showing the smallest differentiation (Fst = 0.017), and the (Qinnan) QN and (Yinhai) YH populations showing the greatest differentiation (Fst = 0.409). UPGMA clustering and structure analysis (K = 2) divided the 12 populations into two subgroups. Overall, our research suggests that the genetic diversity of the wild population of A. polyzonata in the Guangxi region has declined. Thus, prioritizing the protection of highly genetically diverse populations, such as the LA population, is urgently needed. This study provides a scientific basis for the protection and sustainable utilization of A. polyzonata resources in Guangxi.

In this study, we conducted molecular identification and complete mitochondrial genome annotation of isopod parasites isolated from mud crabs (Scylla paramamosain) in the China Sea. The specimen was identified as Portunion sinensis, a recently described species of the family Entoniscidae. P. sinensis is characterized by an anterior thorax positioned vertically and posterior ventral processes directed backwards; the female’s marsupium is formed by the close adhesion of oostegites to the host membrane; the first oostegite is differentiated into three parts; the pleopoda have well-developed lamellar and pleural lamellae; and two ventral ovarian processes are present along with a pair of dorsal processes. The complete mitochondrial genome of the parasite is 14,603 bp in length, containing 35 genes (13 protein-coding genes, 20 transfer RNAs, and 2 ribosomal RNAs) as well as a putative control region (CR) located between the cob and nad1 genes. This study represents the initial characterization of the mitochondrial genome of P. sinensis. These findings provide molecular validation of its status as an independent species and lay the groundwork for the future identification of parasites within the genus Portunion. These data provide a necessary molecular reference for future research into the systematics and evolutionary history of decapod-infesting parasites.

We report the first complete mitochondrial genome of the marine wood borer Dicyathifer mannii from Beihai, China. The genome is 17,158 bp long, containing 12 protein-coding genes, 22 transfer RNAs, and 2 ribosomal RNAs. The nucleotide composition is 40.7% T, 12.1% C, 21.8% A, and 25.5% G. Phylogenetic analysis indicates that the Beihai specimen clusters with conspecifics from Hainan, China, distinct from the Philippine population. This study provides valuable genomic resources for future research on D. mannii.

Ammonia-nitrogen is a key environmental factor that affects fish survival. Previous studies have mainly focused on the physiological and biochemical responses of commercially farmed fish to ammonia-nitrogen, while the responses of endangered fish species in conservation aquaculture have received far less attention. This study investigated the effects of acute ammonia-nitrogen stress on the physiological performance of an endangered fish species, Procypris mera, through physiological, biochemical, transcriptomic, and metabolomic analyses. One-and-a-half-year-old juvenile P. mera (8.35 ± 0.77 g) were exposed to three ammonia-nitrogen concentration gradients: a control group (freshwater), a low-concentration group (1.6 mg/L), and a high-concentration group (3.2 mg/L) for durations of 6 h, 12 h, 24 h, 48 h, and 96 h. Key enzyme activity indicators related to oxidative stress and immune defense were measured at each exposure duration. Additionally, the liver transcriptome and metabolome of the juvenile P. mera were analyzed to elucidate the characteristics of their physiological and biochemical responses. The results showed that the 96 h half-lethal concentration (96 h LC₅₀) for P. mera was 5.33 mg/L, and the safe concentration was 0.53 mg/L, both of which were significantly lower than those of other Cyprinidae species, such as Carassius auratus, Cyprinus carpio, and Hypophthalmichthys molitrix, suggesting limited tolerance of P. mera to ammonia-nitrogen stress. Continuous exposure for 96 h led to a significant decrease in superoxide dismutase (SOD) and catalase (CAT) activity, indicating that stress intensity exceeded the regulatory limits of the antioxidant system. In contrast, the activities of acid phosphatase (ACP) and alkaline phosphatase (ALP) exhibited a trend of initially increasing and then decreasing with prolonged exposure, reflecting the self-repairing capabilities of P. mera under low concentrations of ammonia-nitrogen. Transcriptomic analysis revealed the central regulatory roles of lysosomal autophagy-mediated clearance, transmembrane transport-mediated detoxification, and the NF-κB inflammatory signaling pathway in the stress response. Metabolomic analysis further suggested involvement of ABC transporter pathways, potential LysoPCs-driven inflammatory cascades, and antioxidant defenses associated with folate and ascorbic acid metabolism. These findings enhance our understanding of the adaptive responses of endangered fish to ammonia-nitrogen stress, provide an analytical framework for investigating the molecular basis of environmental stress responses in these species, and underscore the critical importance of strictly controlling water ammonia-nitrogen levels in conservation aquaculture.