Global warming imposes increasing thermal stress on freshwater ectotherms, yet the molecular mechanisms underlying chronic heat stress adaptation in gastropods remain poorly understood. In this study, we integrated physiological assays with transcriptomic and metabolomic analyses to investigate the time-dependent responses of the hepatopancreas of Bellamya purificata under prolonged high-temperature stress (32 ± 0.5°C) over 56 days. Physiological results revealed dynamic alterations in antioxidant and immune parameters, including sustained suppression of catalase (CAT) and polyphenol oxidase (PPO) activities, a mid-term elevation of superoxide dismutase (SOD) activity, and a late-stage recovery of lysozyme (LZM) accompanied by malondialdehyde (MDA) accumulation. Transcriptomic analysis identified 40, 353, and 342 differentially expressed genes at 7, 28, and 56 d, respectively. Key heat shock protein genes (hsp70b2, cryab, and cryaa) and legumain (lgmn) were consistently up-regulated across all time points. Mfuzz clustering revealed phased adaptive strategies: early activation of chitin synthesis, calcium signaling, and endoplasmic reticulum stress pathways; mid-phase enhancement of DNA repair and protein homeostasis; and late-stage induction of lysosomal degradation and immune modulation. Metabolomic profiling identified numerous differentially accumulated metabolites, primarily including glycerolipids, glycerophospholipids, fatty acyls, and so on. Lipid metabolism pathways such as glycerophospholipid, ether lipid, and arachidonic acid metabolism were significantly enriched, with marked changes in marker metabolites including glycerophosphocholine, phosphorylcholine, and arachidonic acid. Integrative multi-omics analysis highlighted coordinated regulation of phospholipid metabolism at both transcriptional and metabolic levels, with up-regulation of CDP-choline and down-regulation of lysophospholipids. Weighted gene co-expression network analysis (WGCNA) further identified SOD-correlated gene modules and LZM-correlated metabolite modules, pinpointing hsp70b2 and lgmn as hub genes linking oxidative stress responses to immune-metabolic crosstalk via antigen processing and lysosomal pathways. This study provides comprehensive molecular insights into thermal adaptation in freshwater snails and offers potential biomarkers for breeding heat-resilient aquaculture strains.

Bellamya limnophila is a mollusk of significant medical and economic value in China. Understanding the complete mitochondrial genome of this species will better establish a foundation for systematic classification research on Viviparidae. Therefore, we sequenced the complete mitochondrial genome of B. limnophila, conducted a comprehensive analysis of its structural characteristics, and constructed a phylogenetic tree using maximum likelihood and Bayesian methods. The results showed that the genome sequence is 16,991 bp in length, including 13 protein-coding genes (PCGs), 20 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (rRNAs), and 1 non-coding region (D-loop). In summary, the Ka/Ks ratios of all PCGs were <1, indicating that purifying selection dominated the evolutionary process of these snails. The entire genome structure exhibited conservative features, such as the majority of start codons being the standard ATG codon and the majority of tRNA genes having the standard cloverleaf secondary structure. B. limnophila and B. quadrata showed collinearity in terms of sequence homology. Phylogenetic analysis indicates that the clade formed by the genera Margarya, Cipangopaludina, and Bellamya is the sister group of the genus Viviparus; Bellamya limnophila is more closely related to B. quadrata than to other species. This study contributes to the mitochondrial genome database of the family Viviparidae and provides valuable insights into the phylogenetic relationships of related snails.

The rice–snail coculture system represents a resource-efficient and high-yielding agroecological model. However, invasion by the exotic species Pomacea canaliculata disrupts its ecological equilibrium. This study examined the influences of P. canaliculata on the Dietary Composition and microbiota of the native snail Bellamya purificata under monoculture (control) and co-culture (invasion stress) conditions during 30-day and 60-day cultivation periods. Results indicate that both the cultivation condition and duration significantly modified the Dietary Composition of B. purificata at the genus level. At 30 days, the co-cultured B. purificata group exhibited no significant difference (p > 0.05) in gut microbial abundance compared to the mono-culture group, while demonstrating decidedly increased α-diversity and distinctly altered community structure (p < 0.05). The relative abundance of Acinetobacter was remarkably increased (p < 0.05), whereas multiple beneficial bacterial taxa were significantly decreased (p < 0.05). Functional prediction analysis revealed dramatically enhanced enrichment of neurodegenerative disease pathways (p < 0.05) but considerably reduced enrichment in immune disease pathways and signal molecule interaction pathways (p < 0.05). At 60 days, comparative analysis between B. purificata co-culture and mono-culture groups revealed no significant differences in gut microbial abundance, α-diversity, and community structure (p > 0.05). However, the relative abundances of the phyla Bacteroidota, Actinobacteriota, and Planctomycetota were appreciably upregulated (p < 0.05). Genera including Aeromonas and Cloacibacterium also exhibited notably increased relative abundances (p < 0.05). Conversely, the relative abundances of genera such as Enterobacter and Enterococcus were notably downregulated (p < 0.05). Functional prediction analysis further demonstrated greatly enhanced enrichment in cellular motility pathways and cell community-prokaryotic pathways (p < 0.05). These results indicate that although stress from P. canaliculata exerted a significant short-term negative impact on B. purificata, regulatory adaptations through gut microbial changes attenuated this adverse effect following prolonged exposure.

Non-alcoholic fatty liver disease (NAFLD) is a primary metabolic disorder that threatens adolescent health globally, with no effective therapeutic agents currently available. Bellamya purificata is a traditional Chinese medicine categorized as "medicinal food", and polysaccharides are among its active components. However, its physicochemical structure remains poorly characterized, and no study has evaluated its effects on NAFLD. In this study, a homogeneous neutral polysaccharide, α-D-glucan (Mw = 6412.704 kDa), was isolated from B. purificata. The structure of the polysaccharide was characterized using monosaccharide composition analysis, methylation analysis, NMR spectroscopy, and scanning electron microscopy. The backbone structure of the polysaccharide comprises →4)-α-D-Glcp-(1→ and →4,6)-α-D-Glcp-(1→, with side chains of α-D-Glcp-(1→ attached to the O-6 position of the 1→4,6)-α-D-Glcp-(1→ sugar residues. Additionally, QSPS-1D effectively reduced weight gain, hepatic lipid accumulation (TC and TG), and inflammatory responses (tnf-α and il-1β) in NAFLD zebrafish. Moreover, QSPS-1D alleviated dysbiosis by inhibiting harmful bacteria (e.g., Stenotrophomonas, Agrobacterium, and Chryseobacterium) and promoting beneficial microbiota (e.g., Rothia), which restored the Firmicutes-to-Bacteroidetes ratio. In parallel, it enhanced the expression of tight junction proteins (zo-1 and claudin-1), leading to the repair of the intestinal mucosal barrier. These findings suggest that B. purificata polysaccharides may be a potential functional food for early NAFLD intervention, with effects potentially associated with the modulation of the gut microbiota.

Eicosapentaenoic acid (EPA) and Arachidonic acid (ARA) are essential for gonadal development, while their optimal ratio remains unclear due to their functionally distinct and potentially opposing roles. This study investigated the effects of different dietary EPA/ARA ratios (0.53, 1.12, 1.54, 2.09, and 2.50) on physiological metabolism, ovarian development, reproductive performance, and larval stress resistance in Cherax quadricarinatus (50.72 +/- 0.40 g). The experimental period included nutritional enhancement (6 weeks), mating, spawning, and larval hatching (8 weeks), and an acute ammonia nitrogen stress test (96 h). The initial group comprised crayfish sampled post-acclimatization and prior to nutritional enhancement. Results revealed that the gonadosomatic index was significantly increased in all treatment groups compared with the initial group (P < 0.05). Compared to the control (0.53), dietary EPA supplementation significantly enhanced lipid metabolism in the hepatopancreas and promoted lipid transport to the ovary via the hemolymph (P < 0.05). The contents of progesterone and 17 beta-estradiol in serum were highest in the 2.09 group, notably exceeding those in the control (0.53) (P < 0.05). Moreover, crayfish in the 2.09 group exhibited upregulated expression of citrate cycle-related genes in the hepatopancreas and elevated contents of related metabolites in the ovaries, indicating enhanced energy anabolism (P < 0.05). N-glycan metabolism pathways in the hepatopancreas were significantly enriched in the 2.09 group (P < 0.05), suggesting increased synthesis of exogenous vitellogenin. Additionally, crayfish in the 2.09 group enhanced non-specific immune responses against inflammatory stress by activating the CYP450 pathway and phenoloxidase system (P < 0.05). In summary, a dietary EPA/ARA ratio of 2.09 enhances lipid metabolism, stimulates sex hormone and vitellogenin synthesis, and mitigates inflammatory responses, thereby supporting healthy ovarian maturation and improving reproductive capacity in C. quadricarinatus. Regression analysis estimated the optimal dietary EPA/ARA ratio for promoting ovarian development and reproduction in C. quadricarinatus female broodstock to be between 1.60 and 2.21.

Cipangopaludina chinensis is a unique species with both medicinal and culinary applications, offering significant economic and nutritional benefits in China. However, the large amount of fishing and the invasion of other species have severely impacted the natural resources of C. chinensis in China. Moreover, the molecular-level population structure of C. chinensis remains poor. In this study, the genetic diversity and population structure of 10 different geographical populations of C. chinensis from Guangxi, China, were analyzed using microsatellite DNA markers. The results showed that a total of 176 alleles in the populations were detected by 12 microsatellite markers. The polymorphism information content (PIC) was 0.523-0.918, indicating that these markers were highly polymorphic (PIC > 0.5). The observed heterozygosity (Ho) and expected heterozygosity (He) of the 10 populations were 0.156 (RS)-0.533 (NN and WZ) and 0.186 (RS)-0.702 (QZ), respectively. This indicated that the genetic diversity of NN, RA, and WZ populations was relatively high, while the genetic diversity of HC, NP, and RS populations was low. The genetic diversity of the remaining four populations was at a medium level. AMOVA analysis showed that high genetic differentiation was found among the populations (Fst=0.313, P < 0.001), and the genetic variation within populations (69 %) was greater than among populations (31 %). The genetic structure results revealed that all populations could be divided into two genetic clusters, which was confirmed by the UPGMA tree constructed based on Nei's unbiased genetic distance and PCoA analysis. These findings provide important genetic information for C. chinensis and a theoretical basis for future protection and selective breeding between different geographical populations.

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.

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.

Body coloration is a key phenotypic trait with ecological and economic significance in fish. In this study, we investigated the genetic basis underlying body color differences between two closely related carp varieties, Cyprinus carpio var. Jinbian (J-type, characterized by metallic body coloration) and C. carpio var. Quanzhounensis (H-type, characterized by translucent body coloration). By constructing an F2 population and integrating histological examination, transmission electron microscopy, bulked segregant analysis (BSA-seq), and transcriptome analysis, we identified both phenotypic and molecular contributors to color variation. Ultrastructural analysis revealed that the translucent phenotype of H-type individuals was associated with the absence of guanine crystals in iridophores. BSA-seq detected two major QTLs on chromosome 1 (9.7-12.3 Mb and 12.4-25.9 Mb), which encompassed several genes related to pigment cell development. Among them, GART, involved in purine biosynthesis, was significantly upregulated in J-type individuals (log2(FC)= 1.44), consistent with the observed guanine accumulation. Other genes such as arl6 and Vangl1, although not differentially expressed, remain of interest due to their known roles in pigmentation pathways. These findings provide new insights into the molecular mechanisms of body coloration in C. carpio and lay the groundwork for further functional studies.

Oreochromis aureus is an economically valuable fish species, but its domestication in saline environments remains unexplored, with limited reports on how salinity stress affects its physiological functions and acclimation-related mechanisms. Thus, this study collected O. aureus exposed to different salinity stress levels (0 %o , 3 %o , 7 %o , and 11 %o ) and analyzed their growth performance, histopathology, physiological functions, and transcriptome. The results showed that salinity stress had no significant effect on growth performance. Salinity stress damaged gill tissues, decreased physiological and antioxidant activities, increased osmotic and antimicrobial activities, and altered digestive functions. Comparative transcriptome analyses identified 38,910 differentially expressed genes (DEGs), of which 11,488 were common to the three comparisons. These DEGs were significantly associated with specific salinity stress response-related KEGG pathways, including Sphingolipid signaling pathway, Lysosome, Phagosome, and Focal adhesion. The present results identify 1 GO term (regulation of biological proces) in response to salinity stress. Furthermore, 15 candidate genes related to salinity stress responses and physiological functions were also identified. (e.g., TLR2, NCF2, Sptlc2, and ctsd). On the basis of GO, KEGG and STEM analyses, the data enabled the development of a mechanistic model that details how O. aureus adapts to salinity stress by regulating physiological changes. Finally, RT-qPCR assays verified the accuracy and reliability of the high- throughput sequencing results. This study enhances our understanding of O. aureus adaptive strategies under salinity stress, while also providing relevant theoretical insights into the domestication of fish under saline conditions and the mechanisms mediating adaptations to saline aquatic environments.

Cipangopaludina chinensis, as a financially significant species in China, represents a gastropod in nature which frequently encounters starvation stress owing to its limited prey options. However, the underlying response mechanisms to combat starvation have not been investigated in depth. We collected C. chinensis under several times of starvation stress (0, 7, 30, and 60 days) for nutrient, biochemical characteristics and transcriptome analyses. The results showed that prolonged starvation stress (> 30 days) caused obvious fluctuations in the nutrient composition of snails, with dramatic reductions in body weight, survival and digestive enzyme activity (amylase, protease, and lipase), and markedly enhanced the antioxidant enzyme activities of the snails. Comparative transcriptome analyses revealed 3538 differentially expressed genes (DEGs), which were significantly associated with specific starvation stress-responsive pathways, including oxidative phosphorylation and alanine, aspartate, and glutamate metabolism. Then, we identified 40 candidate genes (e.g., HACD2, Cp1, CYP1A2, and GPX1) response to starvation stress through STEM and WGCNA analyses. RT-qPCR verified the accuracy and reliability of the high-throughput sequencing results. This study provides insights into snail overwintering survival and the potential regulatory mechanisms of snail adaptation to starvation stress.

Cyprinus carpio var. Quanzhounensis, native to Quanzhou County, Guilin City, Guangxi, has a dark brown body color, translucent gill cover, and abdominal skin, and is an important farmed species in the local integrated rice-fishery industry. A comparative study on the skin of Cyprinus carpio var. Quanzhounensis revealed a lack of reflective guanine crystals on the body surface and a significantly higher melanin content than that of C. carpio var. Jian, which was tentatively considered the direct cause of variations in body color of this group. Iridocytes are a pigment cell species that contain regularly arranged guanine crystals, which are the key material basis for the metallic luster of the fish body surface. In species such as medaka (Oryzias latipes) and zebrafish (Danio rerio), the absence of guanine crystals is considered a manifestation of the absence of iridocyte differentiation and therefore is ideal for studying the mechanism of pigment cell differentiation. The pnp4a, Gbx2, sox10, tfec genes and other iridocyte-related genes have been mined using mutant materials, and we have uncovered the differentiation mechanism that regulates the formation of iridescent cells. C. carpio var. color has abundant genetic variation in body color and is a good material for studying the mechanism of body color determination in fish. The roles of ASIP and MC1R in the aggregation and distribution of melanin and formation of black spots in C. carpio var. color were verified. The guanine crystalline deletion trait of C. carpio var. Quanzhounensis may be loaded with regulatory mechanism diversity and mutation loci related to guanine crystal formation or iridescent cell differentiation. In addition, as a rice-fish culture species, the living environment of C. carpio var. Quanzhounensis harvestmen differ significantly from pond and net-pen culture species, requiring high resistance to disease, adversity, and transport. It is unclear whether the absence of guanine crystals in their skin leads to changes in their basal physiological state, and in-depth studies are beneficial for accurate assessment of culture performance. To reveal the structural basis and transcriptomic characteristics of guanine crystalline deficiency traits in the skin of C. carpio var. Quanzhounensis in this study, we selected the subscale tissues with the most significant differences in guanine crystalline distribution as the control material, and transmission electron microscopy was used to observe the tissue structure and full-length transcriptome sequencing to understand the structural and transcriptomic characteristics of guanine crystalline deficiency in the skin of C. carpio var. Quanzhounensis. The results of this study provide information for the analysis of body color traits, identification of economic traits, and utilization of germplasm resources. Transmission electron microscopy of the subscale tissue sections revealed two significant differences in the histological structure of C. carpio var. Quanzhounensis, and C. carpio var. Jian. First, guanine crystals were absent in C. carpio var. Quanzhounensis, whereas guanine crystals were widely present in the tissues of C. carpio var. Jian and cascading cavities were observed in the sections after guanine crystals were dislodged. Second, the number and density of melanin particles in the tissues of C. carpio var. Quanzhounensis harvestmen were significantly higher than those of C. carpio var. Jian, showing smaller, darker, and more numerous particles, which is consistent with the darker color and lack of silvery reflective material on the body surface of C. carpio var. Quanzhounensis harvestmen. The transcriptome characteristics were analyzed using Oxford Nanopore (ONT) sequencing technology, and 2.88~3.26 Gb of high-quality data were obtained for each sample. The number of full-length sequences after filtering ribosomal RNA for all sample data was 2 203 826~2 412 500, and the proportion of full-length sequences for each sample was 87.06%~88.57%. The comparison rate was 90.35%~92.46%. Variable splicing events in the transcripts were counted; 3 075 variable splicing events and 57 624 variable polyadenylation events were detected; and 15 615 new coding region sequences and 771 long-stranded non-coding RNAs were predicted. The number of exon jumps and intron retention in variable splicing events differed significantly (P<0.01) between species, and the number of transcripts with five polyadenylation sites differed significantly (P<0.01) between species, indicating that variable splicing and polyadenylation are involved in regulatory processes related to trait formation. A total of 15 615 open reading frames (ORFs), including 9 890 complete ORFs, were predicted in this study. A total of 841 differentially expressed transcripts were screened in this study; 183 transcripts were upregulated and 658 transcripts were downregulated in C. carpio var. Quanzhounensis compared to C. carpio var. Jian (JH), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed enrichment in extracellular matrix-receptor interactions and adherent spots. KEGG pathway analysis showed that it was enriched for extracellular gaps, transcription factor complexes, integrin complexes, and other terms. The most significantly enriched KEGG pathway and GO terms were closely associated with the extracellular matrix, and it is speculated that these transcriptional changes may lead to changes in the composition, density, and conformation of the skin extracellular matrix.

A 60-day culture in brackish water (0, 3, 5, 7, 9, and 11 ppt) was conducted to study the effects of salinity on muscle nutrition, fatty acid composition, and anabolic metabolism of blue tilapia Oreochromis aureus. Current research showed that WGR, SGR, and FCR indicators of tilapia were better improved in brackish water. In addition, the physical properties of O. aureus muscle demonstrated a positive correlation with salinity levels. The content of amino acids and fatty acids in O. aureus muscles grown under salinity was higher than that in freshwater ( P>0.05 ). Venn analysis showed that 2343 common differentially expressed genes (DEGs) were identified in the four groups (0, 3, 7, and 11 ppt), of which 767 were up-regulated and 1576 were down-regulated. GO and KEGG analysis revealed 39 significant pathways, mainly including unsaturated fatty acid biosynthesis, fatty acid elongation, and α-linolenic acid metabolism. The heat map and trend analysis showed that the expression levels of key genes involved in the physiological processes of ELOVL, SPLA2, and FADS2 in the test group were significantly higher than those in the control group ( P>0.05 ). The above results suggested that O. aureus can not only adapt to the saline habitat but also improve muscle quality by regulating the body’s metabolic pathways.

Bellamya purificata is an important medicinal value and economically farmed species in China. However, because little is known about the genetic characteristics of this species, the utilization of high-quality germplasm resources is hindered. The study examined the genetic differentiation between, and the structure of 12 B. purificata populations in Guangxi using 7 microsatellite DNA markers. High genetic diversity occurred in each population, with mean observed heterozygosity 0.655 and a mean expected heterozygosity 0.832. Analysis of molecular variance reveals genetic diversity to be greater within (95.2%) than among populations (4.8%). Genetic differentiation between populations is weak (Fst = 0.048, P < 0.001), with mixing of genetic clusters prevalent at the level of the individual. Genetic flow exists between populations (Nm = 3.084-11.778), with Longshui and Guilin populations exchanging frequently. A Mantel test reveals a low correlation between geographic and genetic distances (r = 0.2482, P < 0.071), suggesting that dispersal between neighboring populations facilitates population exchange. No significant heterozygosity excess was observed for any population (P > 0.05), indicating a lack of recent genetic bottlenecks. The results provide important genetic information for B. purificata, and data for potential germplasm discovery and aquaculture development.

The rice flower carp ( Cyprinus carpio ) is an important fish in integrated rice-fishery farming. Here, we performed the first genome-wide association study (GWAS) for seven growth traits (including body mass, total length, body length, body height, body width, caudal-peduncle depth, and eye spacing) in 200 rice flower carp samples using 369,688 high-quality SNPs and 42,225 indels obtained by double-digest genotyping-by-sequencing (ddGBS). The morphometrics of these traits were highly correlated (Pearson’s correlation coefficients = 0.74–0.99, p < 0.001). GWAS detected 15, 5, 4, 26, 7, 16, and 17 loci significant associated (-log10P ≥ 5) with body mass, total length, body length, body width, body height, caudal-peduncle depth, and eye spacing, respectively. Subsequently, within the 50 kb upstream and downstream regions surrounding these significant loci, 38, 19, 18, 20, 52, 27, and 37 candidate genes for the seven growth traits were detected, respectively. Importantly, B6_4352672 and A8_4978825 were significantly associated with more than five growth traits. These results showed loci significantly associated with more than five growth traits will be helpful for future marker-assisted selection (MAS). Interestingly, chromosomes A8 and B25 had many loci significantly associated with growth traits, most of which were shared among multiple growth-related traits. These results indicated that chromosome A8 and B25 may be closely related to growth traits. Our findings not only help understand the genetic architecture of growth traits in fish but facilitate the identification of candidate genes for marker-assisted selection towards breeding faster-growing rice flower carp in the future.

Background This study aimed to investigate the genetic molecular mechanism of body color differentiation and variation of red tilapia, selecting the main genes related to the variation and cultivating the pure and stable red tilapia variety. Results The effects of different temperature treatments on body color and survival of Guam red tilapia, pearl white red tilapia and Florida red tilapia were compared. Besides, comparative transcriptome analysis was used to screen the candidate genes linked to the skin color differentiation of pearl white red tilapia. Among them, the body color of Guam red tilapia changed when the water temperature dropped to 16 − 14 °C, and continued to drop to about 11 °C, it was discolored in a large area reaching above 90%. According to the differential analysis: Tyrosine Kinase STYK1, HSP70, HSP30 and Transcription factor Sp6 expressions were significantly increased in the low temperature group, while MC1R, Transcription factor (MafB, jun-D, AP-1, E2F5, ETV6, Sp9, Sp7, E2F1, Sp4) expressions were notably decreased. Conclusions In this study, the expressive quantity of tyrosine protein kinase in the low temperature group HLF7 was significantly higher than that in the normal temperature group HLF3, which indicated that the melanin synthesis ability was enhanced in the low temperature group HLF7. The result was consistent with the tendency of red tilapia to become darker as the temperature gradient decreased.

Low temperatures limit the development of Oreochromis niloticus (tilapia), and an increase in low-temperature tolerance would increase yields. We studied the responses of tilapia to low temperatures. The fish were labeled CK, AA, BB, and CC based on treatment (25°C, 12°C/1 h, 12°C/24 h, and 12°C/48 h, respectively) with CK being the control group. We examined the transcriptome responses and the Na + /K + -ATPase activity of gill tissue in each group. The Na+/K+-ATPase activity varied with the treatment time. Transcriptome sequencing of 12 individuals yielded 585.51 million clean reads, and at least 83.26% of the genes were mapped to the reference genome. Comparative analysis revealed 12,448 genes with significantly differential expression, including 792, 1,827, 1,924 upregulated genes and 992, 3,056, 3,857 genes downregulated for AA, BB, and CC, respectively. Differentially expressed genes (DEGs) were validated using RT-PCR for five genes. Functional annotation analysis of the DEGs identified functions associated with response to low-temperature stress. When tilapia was subjected to low-temperature stress, expression changes occurred in genes associated with cytokine-cytokine receptor interaction, metabolic pathways, cell adhesion molecules, material transport, and immunity. The founding will help understand the effects of low temperature on fish and provide a theoretical basis for the tilapia breeding industry.

Astaxanthin (AST) is a feed additive applied in aquaculture, which has been proved to promote the growth performance, antioxidant capacity and immunity of crayfish (Procambarus clarkii), an important economic fishery species in China. However, the underlying mechanism of improved antioxidant capacity of AST in crayfish remains unknown. In this study, changes of antioxidant activity, transcriptome and metabolome in crayfish hepatopancreas were analyzed after feeding with AST. The results showed that AST could improve the antioxidant capacity of crayfish via increasing antioxidant enzymes activity and reducing malondialdehyde content. Transcriptomic analysis revealed that immune system, cell death and disease, mitochondrial respiration and oxidative phosphorylation pathways were altered with AST feeding. AST significantly increased total cholesterol level indicated the metabolism of crayfish was affected. Metabolomic analysis revealed the alteration of mineral adsorption, carbon and amino acid metabolisms, and fatty acid biosynthesis. Conjoint analysis of transcriptome and metabolome suggested that AST predominantly regulated amino acid and fatty acid metabolisms. Taken together, AST acts on crayfish mainly through improving antioxidant capacity and modulating amino acid and fatty acid metabolisms.

Abstract As the main economic fish species in integrated rice-fish farming, the growth performance of rice flower carp (Cyprinus carpio var. Quanzhounensis) directly affects farmers’ economic benefits. In this study, whole-brain and liver tissues of rice flower carp of different sizes were used for transcriptome analysis to identify differentially expressed genes (DEGs) in the two organs and to determine genes associated with the growth of rice flower carp. In the liver tissues, 28,186 genes were generated, including 880 DEGs. In the brain tissues, 50,373 genes were generated, including 2223 DEGs. Twelve and eight genes from the liver and brain, respectively, were selected for quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The high correlation between the expression of these genes in RNA-seq and qRT-PCR provided reliable transcriptome information. The transcriptome results suggested that the slow-growth individuals were affected by the feeding regulators, neuropeptide y (NPY) and cholecystokinin (CCK), less food was uptake and needed to maintain normal life activities through lipid metabolism and gluconeogenesis in the liver, thus, reducing the amount of energy available for growth and resulting in slow growth. This study provides new insights into the growth regulation mechanisms of rice flower carp and increases our understanding of growth regulation mechanisms in different fish species.

Cipangopaludina chinensis is an important economic value snail species with high medicinal value. The gut microbes of aquatic animals plays a vital role in food digestion and nutrient absorption. Herein, we aimed at high-throughput sequencing of 16S rRNA to further investigate whether there were differences in the composition and function of gut microbes of adult and juvenile C. chinensis snails, as well as sediments. This study found that the microbial diversity of the sediment was significantly higher than that of the snails gut (P < 0.001), but there was no significant difference between the gut flora of adult and juvenile snails (P > 0.05). A total of 47 phyla and 644 genera were identified from all samples. Proteobacteria and Verrucomicrobia were the two dominant phyla in all samples, and overall relative abundances was 48.2% and 14.2%, respectively. Moreover, the relative abundances of Aeromonas and Luteolibacter in the gut of juvenile snails (30.8%, 11.8%) were higher than those of adults (27.7%, 10.6%) at the genus level (P > 0.05). Then, four indicator genera were found, namely Flavobacterium, Silanimonas, Geobacter and Zavarzinella, and they abundance in the gut of juvenile snails was significantly higher than that of adults (P < 0.05). This results imply the potential development of Silanimonas as a bait for juvenile snail openings. We observed that Aeromonas was the primary biomarker of the snail gut and sediments (P < 0.001), and it may be a cellulose-degrading bacteria. Function prediction revealed significantly better biochemical function in the snail gut than sediments (P < 0.001), but no significant differences in adult and juvenile snail (P > 0.05). In conclusion, studies show that the snail gut and sediment microbial composition differ, but the two were very similar. The microbial composition of the snail gut was relatively stable and has similar biological functions. These findings provide valuable information for in-depth understanding of the relationship between snails and environmental microorganisms.