Salinity is an important ecological factor affecting the osmolality of aquatic animals. Solenaia oleivora is an endemic and economically important freshwater shellfish in China. However, its osmotic response and osmoregulatory mechanisms under high salinity stress are still unclear. In this study, S. oleivora was exposed to saline water (salinity: 2.2‰) for 3 h, 6 h, 12 h, 24 h, and 48 h, and then the changes in osmolality, ion concentrations, free amino acid (FAA) content, Na⁺/K⁺-ATPase (NKA) activity, and gill histology were analyzed. The hemolymph osmolality increased from 3 h after salinity stress and stabilized between 24–48 h. Na⁺ in the hemolymph increased from 24 h after salinity stress, and Cl⁻ increased from 3 h. The content of total FAAs in the hemolymph increased after salinity stress. The content of alanine, glycine, glutamine, proline, and other FAAs increased after salinity stress. NKA activity in the gill, hepatopancreases, adductor muscle, and axe foot decreased during 3–48 h of salinity stress. The gill filament space increased and the number of gill cilia decreased after salinity stress. Principal component analysis (PCA) showed that the first two principal components (PC1 and PC2) cumulatively explained 77.6% of the total variation. The NKA activity was positively associated with PC1, while the ion concentration and most FAAs were negatively associated with PC1. Thus, these results indicated that S. oleivora is an osmoconformer, and inorganic ions, FAA, NKA, and gill structure changes play an important role in its osmoregulation.

Both fish gills and guts can support lots of microbiota that play important roles in the health and growth of hosts. Although the microbiota of silver carp has been widely studied, the data on microbial variation according to fish tissues and local habitats are lacking. In this study, the microbes in the guts and gills of silver carp (Hypophthalmichthys molitrix) from the hydrophyte-dominated region (zone H) and the algae-dominated region (zone A) of Taihu Lake in autumn were analyzed. Proteobacteria, Cyanobacteria, and Firmicutes were the dominant bacteria in silver carp. The microbial diversity was higher in the gills than that in the intestines, and higher in fish from zone H than that from zone A. Beta diversity analysis revealed significant differences in microbial community structures between gill and guts, and between fish from the two habitats. Gills had a higher abundance of phyla Actinobacteria, Bacteroidetes, and Deinococcus-Thermus, and a lower abundance of verrucomicrobia than the intestine. Both tissues possessed indicator taxa, while many indicator taxa in the gill were conditional pathogens. Compared to fish from zone H, fish from zone A had more abundant Cyanobacteria, and less abundant Proteobacteria and Bacteroidetes. PICRUSt2 analysis revealed that fish microbial functions were mainly associated with metabolism, replication, repair, folding, sorting, and degradation. These results showed that the microbial community of silver carp from Taihu Lake varied according to tissues and habitats.

Air exposure is a common stress for Corbicula fluminea, an economically important freshwater shellfish consumed in China, during aquaculture and transportation. However, little is known about its molecular responses to air exposure. Therefore, this study used a combination of PacBio full-length and Illumina transcriptomes to investigate its molecular responses to air exposure. A total of 36,772 transcripts were obtained using PacBio sequencing. Structural analysis identified 32,069 coding sequences, 1906 transcription factors, 8873 simple sequence repeats, and 17,815 long non-coding RNAs. Subcellular localization analysis showed that most transcripts were located in the cytoplasm and nucleus. After 96-h of air exposure, 210 differentially expressed genes (DEGs) in the gill were obtained via Illumina sequencing. Among these DEGs, most of the genes related to glycolysis, tricarboxylic acid cycle, lipid metabolism, and amino acid metabolism were upregulated. Additionally, many DEGs associated with immunity, cytoskeleton reorganization, autophagy, and ferroptosis were identified. These findings indicated that metabolic strategy change, immune response, cytoskeleton reconstruction, autophagy, and ferroptosis might be the important mechanisms that C. fluminea use to cope with air exposure. This study will enrich the gene resources of C. fluminea and provide valuable data for studying the molecular mechanisms coping with air exposure in C. fluminea and other freshwater mollusks.

To explore the effects of different plant combinations in ecological floating beds on water quality purification and phytoplankton community structure in shallow eutrophic lakes, we conducted a survey of phytoplankton communities within ecological floating beds featuring distinct plant combinations in Meiliang Bay, Lake Taihu, during June and August 2021. The study focuses on two combinations: EA (Canna indica + Acorus calamus + Phragmites australis) and ES (Canna indica + Oenanthe javanica + Sagittaria sagittifolia). Results indicated that ecological floating beds significantly improved water quality, with the strongest restoration effects observed in the EA area. Specifically, turbidity was reduced by 47–89%, while chlorophyll a (Chl-a) concentration inhibition rates reached 82% in June and 54% in August. The comprehensive trophic state index (TLI) remained stable at levels indicating slight eutrophication (≤58.6). Phytoplankton community structure shifted from dominance by eutrophic functional groups (primarily FG M) toward greater diversity. In the EA area, the number of dominant functional groups increased from five (control) to six, and the abundance of the key cyanobacteria group (FG M) declined from 18.29% (control) to 7.86%. Redundancy analysis (RDA) revealed temporal changes in driving factors: nutrients were primary in June (explanation rate: 64.7%), while physical factors dominated in August (explanation rate: 51.2%). This study demonstrates that installing ecological floating beds with diverse plant combinations in shallow eutrophic lakes can effectively alter phytoplankton community structure and enhance in situ water restoration. Among the tested combinations, EA (Canna indica + Acorus calamus + Phragmites australis) exhibited the optimal restoration effect. These findings provide a scientific basis for water environment protection and aquatic biological resource restoration in shallow eutrophic lakes.

The Chinese mitten crab (Eriocheir sinensis) is widely distributed along eastern China, where northern and southern populations may have evolved different environmental adaptation mechanisms. DNA methylation, as an important epigenetic modification, plays a key regulatory role in environmental adaptation. In this study, muscle and hepatopancreas tissues from E. sinensis populations of the Liaohe River (LH) and Beilunhe River (BLH) were subjected to integrated RNA-seq and whole-genome bisulfite sequencing (WGBS) analyses, generating 12 mRNA libraries and 12 DNA methylation libraries. RNA-seq analysis identified 622 and 783 differentially expressed genes (DEGs) in muscle and the hepatopancreas, respectively, in the LH group compared with the BLH group, with downregulated genes accounting for a larger proportion. WGBS analysis showed that genome-wide DNA methylation in E. sinensis was predominantly in the CG context, with the highest methylation levels observed in gene body regions. A total of 972 and 991 differentially methylated regions (DMRs) were identified in muscle and the hepatopancreas, respectively. Integrated analysis further identified 10 differentially methylated and expressed genes (DMEGs) in muscle and 26 DMEGs in the hepatopancreas. Notably, no single fixed pattern was observed between methylation changes and gene expression changes in either tissue. These findings suggest that DNA methylation may participate in environmental adaptation in northern and southern populations of E. sinensis by modulating gene expression. Our results highlight the important role of epigenetic regulation in the evolutionary adaptation of crustaceans to different environments and provide a theoretical basis for the development of environment-associated molecular markers and the evaluation of adaptive germplasm resources.