Marine ranching is increasingly used in coastal management, yet its impacts on ecosystem stability and carbon cycling are still poorly understood. Here, we integrated stable isotope analyses (δ13C and δ15N) with a summer Ecopath model to quantify trophic structure, carbon-flow pathways and system attributes in the Haizhidu marine ranching area (MRA) of the Bohai Sea, China, in comparison with an adjacent control area (CA). We specifically examined the intrinsic linkages between carbon transfer routes and indicators of ecosystem maturity and stability. Under summer conditions, the MRA exhibited substantially higher total system throughput, total biomass, respiration, and primary production than the CA, indicating an enlarged system scale and improved trophic development. Carbon-flow pathways were more complex and denser in the MRA, particularly between trophic levels II-IV, with the number of carbon-flow channels being nearly fifteen times that of the CA. A larger proportion of carbon was retained within low-trophic-level groups in the MRA, contributing to greater carbon storage and slightly higher transfer efficiency. Spearman correlation analysis showed that enhanced energy recycling and increased carbon-pathway complexity were strongly associated with lower TPP/TR and TPP/TB ratios, suggesting increased ecosystem maturity and stability during the study period. Overall, this summer-specific case study provides preliminary evidence that marine ranching, through artificial reef construction, can modify carbon-flow structure and potentially enhance ecosystem functioning during periods of high biological activity. Multi-season and multi-year monitoring is still required to verify whether these patterns persist across time.

Discovering specific microbial markers and probiotics related to rapid growth offers a route for developing targeted feed solutions. This study was conducted in two phases: Phase I: Using 16 S rRNA sequencing to characterize the intestinal landscape and to discover a significant taxonomic shift in koi (Cyprinus carpio) that grow fast (FG) and grow slow (SG). Phase II: A dietary intervention trial was implemented across four experimental cohorts: a negative control (NC) fed a basal diet and three treatment groups (C1, C2, and C3) supplemented with Exiguobacterium sp. strain WY(Y)3 at escalating concentrations of 1 × 106, 1 × 107, and 1 × 108 CFU/g, respectively. The FG fish (11.44 ± 0.61 cm; 20.81 ± 1.33 g) harbored markedly higher proportions of Cyanobacteriota, Actinobacteriota, Chloroflexota, and notably Exiguobacterium sp., alongside enhanced metabolic pathways related to secondary metabolite biosynthesis compared with the SG fish. A piscine-derived strain, Exiguobacterium sp. WY(Y)3, isolated from the FG, significantly improved growth performance when supplemented in feed, with the 1 × 106 CFU/g producing the best overall outcomes (WGR = 186.26 ± 1.07 and FCR = 1.437 ± 0.08), including higher gut microbial diversity and stability. Integrated microbiome and metabolomic analyses revealed that supplementation with Exiguobacterium enhances growth performance by reshaping gut microbial composition and regulating host energy metabolism. This includes the downregulation of fatty acid β-oxidation and pyruvate metabolism pathways, alongside the upregulation of bile acid synthesis and vitamin-associated pathways (p < 0.05). Collectively, dietary inclusion of 1 × 106 CFU/g of Exiguobacterium sp. WY(Y)3 effectively promotes growth through microbiota restructuring and metabolic optimization, supporting its potential as a probiotic in aquaculture nutrition.

The objective of this research was to investigate the impacts of supplementing both unenriched and enriched live Artemia salina with Chlorella vulgaris and Dunaliella salina in goldfish (Carassius auratus) diets on various parameters, including growth performance, feed utilisation, blood parameters, immunity, histology, and β-carotene levels. The experiment was conducted for 90 days, and all groups of goldfish (initial weight = 2.51 ± 0.01 g/fish, N = 180) received commercial diet supplements (unenriched Artemia (UE), Chlorella-enriched Artemia (CE), Dunaliella-enriched Artemia (DE), and Artemia enriched with both Chlorella and Dunaliella (CDE)). Compared to other fish groups, goldfish given CDE had better final weight, weight gain, average daily gain, specific growth rate, relative growth rate, final length, and length gain, and a lower feed conversion ratio. CDE had the best hematological, antioxidant, and immunity parameters (Immunoglobulin M levels, lysozyme activity, phagocytic activity, and phagocytic index). In addition, goldfish given CDE had the greatest β-carotene content at 8.90 ± 0.4 mg/100 g. Goldfish given enriched Artemia, specifically CDE, exhibited increased intestinal villus length, width, and goblet cells, as determined by histomorphometric analysis (p < 0.05). Additionally, upregulation of MCH, MCH-R, POMC, IGF-1, and TNF-α genes was observed in CDE. In conclusion, supplementing goldfish diets with CDE has several advantages, including improved growth performance, blood parameters, immunity, histology, β-carotene levels, and gene expression related to growth and immunity. The study's results indicate that Artemia enhanced with Chlorella and Dunaliella can improve the health, growth performance, and development of goldfish in aquaculture.

Turmeric (TUR), Curcuma longa, is rich in bioactive substances, and spirulina (SPR), Spirulina platensis, is a source of protein that is highly digestible. This research investigated the combined effects of dietary C. longa and Spirulina platensis on the growth, nutritional composition, coloration, immunity, and gill health of balloon molly fish, Poecilia sphenops, (initial weight = 0.977 +/- 0.003 g) when exposed to acute ammonia stress. Poecilia sphenops (20 fish per aquarium) was distributed into four treatments, each with three replicate aquariums, according to the diets: a basal control diet, a diet supplemented with 0.1% TUR, a diet supplemented with 0.1% SPR, and a diet containing TUR + spirulina 0.1% combined (TUR + SPR). After a 90-day feeding trial, TUR + SPR showed significantly higher growth indicators (average daily gain [ADG] and specific growth rate [SGR]), improved feed efficiency (feed conversion ratio [FCR], protein efficiency ratio [PER], and protein productive value [PPV]), enhanced immunity (immunoglobulin M [IgM], lysozyme activity, and phagocytic activity [PA]), and more vibrant coloration compared to other treatments. The SPR showed improved growth and coloration parameters, also greatest increases in head and caudal peduncle dimensions, while TUR + SPR produced the largest overall increases in body width and length (p < 0.05). Histological analysis of the gills after exposure to acute ammonia stress at the end of the study showed moderately abnormal tissue in TUR, mildly altered tissue in SPR, and normally differentiated tissue in TUR + SPR. Although both TUR and SPR have been individually investigated as feed additives in various fish species, their combined effects, particularly in ornamental fish, remain largely unexplored. The specific knowledge gap addressed by the present study is whether the combination of TUR and SPR at a low inclusion level (0.1% total additives) can simultaneously enhance growth, feed utilization, skin pigmentation, immune parameters, and gill resilience to acute ammonia stress in balloon mollies.

The mechanism underlying the transparent body coloration in goldfish (Carassius auratus) remains unclear. This study employed untargeted metabolomics and transcriptomics analyses of scales, skin, and muscle tissues from transparent goldfish (T) and common goldfish (L), revealing that the transparent phenotype stems from systemic disruption of the purine metabolism network. Metabolomic analysis revealed significant downregulation of guanine and its precursor guanosine across all tissues. Correspondingly, transcriptomic analysis further demonstrated tissue-specific dysregulation of key genes involved in purine synthesis and conversion (mpv17 and pnp4a), collectively preventing iridophore cells from synthesizing sufficient reflector granules and resulting in the loss of structural coloration. Beyond iridophores, this purine metabolic abnormality triggered cascading dysfunctions across the pigment cell network. In melanocytes, the differentiation driver mitfb was upregulated while the synthesis executor tyrp1 was silenced, exemplifying a pattern of enhanced signaling but blocked execution. Compensatory upregulation of the carotenoid transport gene scarb1 also failed to complete pigment deposition. This study, for the first time through integrated metabolomic and transcriptomic analyses, systematically reveals the cascade effects triggered by purine metabolic dysregulation in transparent goldfish and elucidates the molecular mechanism by which purine metabolism disruption impairs iridophore function and further leads to abnormalities in the entire pigment cell system. It offers a new theoretical framework for understanding the evolution and artificial regulation of fish coloration.

To investigate the effects of Lysinibacillus fusiformis on the growth, physiological biochemistry, and intestinal microbiota of pearl gentian grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂), four diets were formulated to contain 0, 1×106, 1×107, and 1×108 CFU/g of L. fusiformis to carry out the feeding trial for 56 days. Each group had three replicates, and the fish had an average initial body weight of (50.0 ± 2.5) g. The results showed that supplementation with L. fusiformis in the feed had no significant effect on the specific growth rate and condition factor of the pearl gentian grouper (p > 0.05), whereas the optimal dose of 1×106 CFU/g significantly improved the survival rate. The diet adding 1×106 CFU/g L. fusiformis significantly increased the crude protein content and decreased the crude lipid content in muscle (p < 0.05). Meanwhile, the optimal dose of 1×106 CFU/g significantly increased the activity of intestinal protease, as well as the activities of hepatic superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) (p < 0.05), while the malondialdehyde (MDA) content was significantly reduced (p < 0.05). At the microbiota level, the optimal dose promoted specific colonization and synergistic co-occurrence with beneficial keystone taxa, which was metabolically mirrored by the up-regulation of central energy intermediates (pyruvate) and the metabolomic enrichment of the intestinal mTOR signaling pathway. Conversely, high doses of supplements (1 x 108 CFU/g) may increase the population of opportunistic pathogens such as Citrobacter, leading to severe metabolic disturbances characterized by the accumulation of long-chain fatty acids (such as docosahexaenoic acid and eicosapentaenoic acid) and the consumption of amino acid dipeptides in the intestinal lumen. Overall, feeding pearl gentian grouper with 1 x 106 CFU/g of Lysinibacillus fusiformis can enhance the survival rate, nutrient deposition in the muscle, antioxidant activity, balance of gut microbiota, and metabolic homeostasis.

Microplastics (MPs) are widespread in water environments and can affect gut microbiota and host metabolism of fish, but whether changes in host metabolism under MPs are mediated by gut microbiota remains unclear. Here, silver carp, a filter-feeding fish with important ecological functions, was in-situ exposure to environmentally relevant MPs. Multi-omics analysis and fecal microbiota transplantation were used to reveal the metabolic responses of carp along gut-liver-muscle axis. After three months of in situ exposure to MPs, community structure of gut microbiota of carp was reshaped, and five dominate phyla were significantly changed, including increased Cyanobacteria, Chloroflexi and Planctomycetota but decreased Firmicutes and Fusobacteriota. Weighted gene co-expression network analysis was further performed between these phyla and liver transcription spectrum, showing that the hub gene module contained up-regulated hppD, maiA and plg and activated ubiquinone and other terpenoid-quinone biosynthesis and phenylalanine metabolism. By fecal microbiota transplantation, the key gene module associated with core microbiota phyla of carp was verified in germ-free zebrafish. Interestingly, up-regulated hppD, maiA and plg and enriched phenylalanine metabolism were also observed in this module. Subsequently, metabolome performed in carp liver also shared activated phenylalanine metabolism, including increased trans-cinnamic acid and L-tyrosine. Furthermore, high-associated mapping showed that the differentially expressed metabolites (gamma-aminobutyric acid, ornithine and L-serine) related to amino acid metabolism in carp muscle were significantly accompanied with increased L-tyrosine in its liver. Overall, MPs exposure could change gut microbiome of silver carp and alter host metabolism especially amino acid metabolism along the gut-liver-muscle axis.

Microplastics (MPs) are ubiquitous in aquatic environments, while their effects on filter-feeding fish are poorly understood. This study aims to explore how MPs change the feeding of planktivorous silver carp. After exposure to MPs, the utilization efficiency of zooplankton by carp increased from 28.45% to 38.63-40.20%, while that of phytoplankton decreased from 50.64% to 40.47-43.32%. MPs did not cause changes in the phytoplankton and zooplankton communities that carp consumed but altered its gut microbiota, leading to increased abundance of genes encoding proteases but decreased carbohydrase genes. Gut metabolomics further showed corresponding metabolic changes especially with increased levels of l-tyrosine, citrulline, succinic acid, and propionic acid, which are significantly correlated with the isotopic signatures of carp utilizing zooplankton. Germ-free zebrafish transplanted with feces of MPs-exposed carp showed metabolic changes like those of carp, verifying that the gut microbiota mediated the effects induced by MPs, while silver carp transplanted with feces of MPs-exposed carp exhibited increased protease activity and enhanced zooplankton utilization efficiency, confirming that MPs could alter its food utilization via gut microbiota. Our findings fill a knowledge gap regarding the ecological risk of MPs to the feeding of planktivorous fish, with potential cascading effects on aquatic ecosystems.

Rice-fish co-culture is a widely adopted sustainable farming practice in China, contributing significantly to global food production. Among the species considered for integration, all-male giant freshwater prawns ( Macrobrachium rosenbergii) show great potential. However, the optimal stocking density for these prawns in rice-prawn co- culture system remains underexplored. This study investigated the effects of six stocking densities: T1 (control), T2 (0.5 prawn/m2), T3 (1.0 prawn/m2), T4 (2.0 prawns/m2), T5 (4.0 prawns/m2), and T6 (8.0 prawns/m2). Key performance indicators, including prawn growth, yield, rice production, food sources, and economic returns, were evaluated. Results showed that T2 (0.5 prawn/m2) achieved the highest prawn body weight but the lowest prawn yield, while T6 (8.0 prawns/m2) resulted in the highest rice yield but the lowest prawn body weight. Stable isotope analysis (delta 13C and delta 15 N) revealed no significant differences in prawn tissue across treatments, with benthic organisms identified as the primary food source, surpassing supplemental feed. Economic analysis indicated that T4 (2.0 prawns/m2) generated the highest net profit and return on investment (ROI). Regression analysis further suggested that a stocking density of 1.85 prawns/m2 maximized the net profit, while 0.90 prawn/m2 yielded the highest ROI. The current study emphasizes that an optimal stocking density of 0.90 prawn/m2 to 1.85 prawns/m2 is recommended for all-male prawns in the rice-prawn co-culture system. These findings could provide a scientific foundation for developing the rice-prawn co-culture model in China and globally, highlighting its significant implications for optimizing cultivation techniques and formulating policies.

The recent resolution of the koi carp (Cyprinus carpio) genome framework through high-throughput sequencing has enabled novel insights into sex determination mechanisms. Whole-genome resequencing (WGS) was performed on koi carp, yielding 1,341,975 high-quality SNPs. Integrated analyses, including gene annotation, GO functional classification, and KEGG pathway enrichment, identified four core genes (sox6, wnt7ba, gnrhr4, and mrps30) significantly associated with vertebrate sex-determination pathways. Validation through PCR-RFLP and Sanger sequencing confirmed that SNP3, a sexually dimorphic locus within the exon region of gnrhr4, demonstrated a sex identification accuracy of 100 % (n = 20).This study not only provides a practical molecular marker for sex-controlled breeding but also advances the theoretical understanding of epigenetic regulatory networks underlying sex determination in teleost fishes.

Intensive farming of fed fish could produce large amounts of uneaten feed and feces, potentially leading to increased nitrous oxide (N2O) emissions. Filter-feeding fish can ingest residual feed and feces, but it is unclear whether introducing them into fed fish farming ponds could reduce N2O emissions. This study employed monoculture of fed largemouth bass (Micropterus salmoides, LB) and polyculture of LB with filter-feeding silver carp (Hypophthalmichthys molitrix, SC) at density ratios of 18:1, 9:1 and 4.5:1 to compare the N2O emission characteristics. The results showed that silver carp could indeed feed on largemouth bass feces, and isotope mixing model indicated that feces was the second largest contributor to the food of silver carp, reaching 14.75 %-15.56 %. However, polyculture of the two species did not or even increased N2O emission flux at water-air interface and its release potential in sediment. Increased mineralization, nitrification and denitrification rates were observed in polyculture systems, particularly at high stocking densities of silver carp. Also, the higher NH4+ accumulation were found across sediment-water interface within polyculture systems. Metagenome revealed that polyculture disturbed the microbial community structure and increased the abundance of Burkholderiales and Steroidobacteraceae. Moreover, polyculture increased the abundance of nitrogen-cycling functional genes, including gdhA, hao, nirB and norB, potentially contributing to the elevated N2O emissions. Structural equation model highlighted that polyculture of largemouth bass and silver carp could drive N2O emissions, mainly through increased sedimental NH4+ concentration and microbial activity. These findings indicate that the introduction of extractive filter-feeding fish into fed fish farming ponds could not reduce N2O emissions, implying the need for optimized management strategies to balance aquaculture productivity with environmental sustainability.

IntroductionMarine ranching is an effective marine ecosystem protection measure that not only helps protect marine resources, but also has an important carbon sink function.MethodsThis study took the Haizhidu marine ranching in the Bohai sea of China as the research object, constructed 20 functional groups in the area, and used the ecosystem model Ecopath with Ecosim (EwE) and stable isotopes (δ13C and δ15N) to model the system, evaluate the biological structure, energy transfer efficiency, and ecological carrying capacity (ECC) of different functional groups in the system, and calculate the carbon sequestration potential when shellfish reach ECC and the impact of marine ranching construction on system stability and maturity.Results and DiscussionThe results of the study on the characteristic parameters of the marine ranching system show that in the Haizhidu marine ranching ecosystem, the functional group with the highest biomass is the sediment detritus functional group (37.75 t/km2), followed by phytoplankton (21.40 t/km2), and the lowest is the other pelagic fishes (0.26 t/km2); the highest trophic level is the Platycephalus indicus (3.70), followed by the 3.43 of Sebastes schlegelii and cephalopods; the energy transfer efficiency is mainly concentrated in the trophic levels I and II. The simulation results of the shellfish ECC show that the ECC of shellfish in this system is 49.21 t/km2. When the system reaches this capacity, the carbon sequestration potential of shellfish is 12.44 t/km2, and the total carbon fixation of the system can increase by 12.90 t/km2. At the same time, the ecosystem showed a high degree of maturity and stability when the shellfish proliferated to the ECC.ConclusionIn general, the results show that in the process of marine ranching management, reasonable control of the number of shellfish can improve the stability of the system and increase its carbon sequestration capacity. The research results can provide a scientific reference for the ecological service function of marine ranching in the future and increase the carbon sequestration service function of marine ranching ecosystems.

Microplastics (MPs) can affect fish health by inducing oxidative stress, but their impact on structural coloration remains poorly understood. This study investigated the effects of environmentally relevant concentrations (16 and 160 μg/L) of MPs and nanoplastics (NPs) exposure on growth, oxidative stress and structural coloration in blue strain guppy fish (Poecilia reticulata). Results showed exposure to 160 μg/L MPs significantly reduced specific growth rate of fish compared to controls. Plastic accumulation followed a dose-dependent pattern, especially within gut concentrations. Oxidative stress responses differed between MPs and NPs: 160 μg/L MPs decreased SOD activity in skin and reduced GSH levels, while 160 μg/L NPs increased MDA levels in gut tissues, indicating severe lipid peroxidation. Structural coloration analysis revealed exposure to 160 μg/L MPs decreased lightness and increased yellowness, demonstrating reduced blue coloration. This was accompanied by an increase in skin uric acid content, suggesting that guanine conversion might occur to combat oxidative stress. These findings demonstrate that MPs, particularly at high concentrations, impair growth and induce oxidative stress in guppies. To counteract stress, guanine in iridophores may be converted into uric acid, leading to a decline in structural coloration. This study is the first to reveal that MPs disrupt structural coloration of fish, providing new insights into the ecological risks of plastic pollution on aquatic organisms.

Aquatic organisms face substantial challenges from climate change, particularly due to rising water temperatures, which significantly impact their growth and survival. This investigation utilized 960 Koi carp (Cyprinus carpio koi) (Initial Body Weight, 0.304 ± 0.005 g). After a 10-day acclimatization period, the fish were distributed equally across 12 glass aquaria (80 × 40 × 45 cm), with three replicates per treatment. This study encompassed two phases. The first phase (10–60 Days Post-Hatching, dph) involved four temperature regimes: T1 (26 °C), T2 (28 °C), T3 (30 °C), and T4 (26/30 °C daily fluctuation). The second phase (60–120 dph) maintained all groups at 30 °C. Initially, T1 exhibited the best growth performance, indicated by the highest Final Body Weight, Weight Gain, Specific Growth Rate (SGR), and Thermal Growth Coefficient (TGC), along with the highest survival rate. Gene expression analysis revealed that HSP70, HSP90, SOD, BCL-2, and FASN were upregulated in T3 and T4, indicative of stress, while MYOD was highest in T1. During the second phase, T4 displayed superior growth and a healthier body composition with elevated moisture and protein, and reduced fat content compared to T1 and T2. HSP70, HSP90, and BCL-2 expression increased significantly in T1, suggesting thermal stress, whereas MYOD levels rose across all treatments, peaking in T4, which correlated with its growth. Further, there were strong relationships among growth parameters, gene expression, and body composition, with T4 exhibiting the highest essential and non-essential amino acids and a unique fatty acid profile. Overall, the results suggest that manipulated temperature significantly influences Koi carp’s characteristics, making it more adaptable to future environmental stress.

Discus fish, Symphysodon spp., have a unique parental care strategy where the fry feed on their parents’ skin mucus after hatching. Here, lipidomics was employed to compare the skin mucus lipid profiles of male or female discus fish during parental and non-parental care. By multivariate statistical analysis, clear separations were found between parental and non-parental female and between parental and non-parental male discus. In the comparison between female discus in the parental and non-parental stages, a total of 107 differentially expressed lipids (DELs) were observed, of which 23 showed increased levels during parental care. For male discus, a total of 108 DELs were found, of which 46 displayed increased levels during parental care. The main DELs were phosphatidyl ethanolamine and phosphatidylinositol, mainly involved in arachidonic acid and sphingolipid metabolism pathways. Further, by comparing parental male and female discus, we found 47 DELs involved in the glycerophospholipid metabolism pathway. Diglyceride showed a higher concentration in the skin mucus of parental females, while phospholipids showed a higher level in that of parental males. Our results revealed changes in the skin mucus lipid profiles of discus fish during parental care, as well as sex-dependent differences between parental fish.

Previous studies have confirmed that the tire microplastic particles (TMPs) have a variety of toxic biological effects. However, the potential toxic mechanisms of TMPs remain to be elucidated, especially in the interaction between particle behavior and seawater warming. In this study, we investigated the effects of three different concentrations of TMPs suspensions (0 mg/L, 1 mg/L, and 500 mg/L) on Alexandrium pacificum in both the presence and absence of warming. Our results revealed significant differences in toxicity among different concentrations of TMPs towards A. pacificum, i.e., low concentrations promoting but high concentrations inhibiting, furthermore, warming exacerbated these toxicological responses. Specifically, under elevated temperature, high concentrations TMPs could inhibit photosynthetic pigment and chlorophyll fluorescence parameter, as well as the nutrient absorption, and induced oxidative stress. Furthermore, TMPs could adsorb onto microalgae surfaces and thus, forming heterogeneous aggregates through agglomeration with extracellular secretions. This is strongly correlated with biomarker response. Overall, these findings highlight the influence of warming on the toxicity of TMPs and provide valuable data for risk assessment.

【Objective】The study was conducted to investigate the genetic diversity of Symphysodon aequifasciatus, analyze the kinship and the genetic differences of a wild population and two artificially bred blue populations, identify candidate genomic regions and loci associated with body color, and provide references for the formulation of classification system of discus fish.【Method】Whole-genome resequencing was conducted on 9 individuals from the wild population (WF), 8 individuals from the solid blue population (BF) and 10 individuals from the albino blue population (ABF), respectively. Single nucleotide polymorphism (SNP) loci were obtained to calculate population genetic diversity indices, analyze population genetic structure, and perform selective sweep analysis between populations. The candidate SNPs were validated by considering SNP annotation and mutation rates combined with PCR and Sanger sequencing.【Result】A total of 1 360 293 SNPs are identified among the 3 Symphysodon aequifasciatus populations. Genetic diversity, as measured by PIC, Pi, Ho, and He, indicates a decreasing trend from the wild population to the solid blue and albino blue populations, with low heterozygosity in the selected populations. Phylogenetic tree, population structure analysis, and principal component analysis of polymorphic loci all indicate that the three populations are independent of each other and cluster within themselves. Linkage disequilibrium decay analysis indicates that the albino blue population is under significant selection pressure, followed by the solid blue population. The result of population selective sweep based on the population differentiation index (FST) and nucleotide polymorphism (Pi) reveals strong selection signals in large regions of chromosomes 3, 12, 13, 18, and 20 in the solid blue population and chromosomes 1, 16, 18, and 19 in the albino blue population. Thirteen and nine candidate SNPs are identified in the solid blue and albino blue populations, respectively.【Conclusion】The genetic diversity of the 3 Symphysodon aequifasciatus populations is relatively low, and the genetic relationships are consistent with the process of artificial breeding. USP43, FGFR2, DENND4, and MLL1 genes may be closely related to the body color formation of Symphysodon aequifasciatus.

The discus fish, Symphysodon spp., a South American cichlid, has a unique parental care behavior where fry bite on parental skin mucus after hatching. In this study, we used LC-MS/MS technique to compare the skin mucus proteome composition of male or female discus fish during parental and non-parental care periods. By multivariate statistical analysis, we found clear separations between different periods and between different sexes of mucus proteome. Compared with non-parental female fish, parental female fish had 283 up-regulated and 235 down-regulated expressed proteins. Compared with non-parental male fish, parental male fish had 169 up-regulated and 120 down-regulated expressed proteins. The differentially expressed proteins for male fish were enriched in sulfur relay system, mucin type O-glycan biosynthesis and antigen processing and presentation pathways, while those for female fish were enriched in sulfur relay system, steroid biosynthesis and complement and coagulation cascades pathways. During the parental care, both male and female discus showed an enhanced lipid metabolism, producing more phospholipids and cholesterol. The difference is that male discus had increased tricarboxylic acid cycle producing more energy during the parental care, while females produced more nucleotides especially guanylic acid. Our study could provide new insights into the understanding of the unique mucus supply behavior of discus fish based on proteomic change.

【Objective】Discus fish (Symphysodon aequifasciatus) has special parental care behavior. In the study, prolactin (PRL) gene from discus fish was cloned and localized and its expression pattern during parental care was analyzed, with an aim to provide a basis for understanding the function of PRL in parental care of discus fish.【Method】A prolactin gene named dfprl was identified by analyzing the whole genome data of the discus fish through BLASTP. The CDS region of dfprl genes were used to design the primer of gene cloing and PCR. The full length of dfprl gene was cloned by RACE technology, and the structure of dfprl gene was analyzed by bioinformatics and its amino acid sequence was analyzed by physicochemical properties and phyletic evolution. Transcriptome sequencing was performed on brain, gonad and skin of discus fish at different rearing stages to explore the expression pattern of dfprl gene during parental care. The dfprl gene in the skin of discus fish was located by paraffin-fluorescence probe-FISH.【Result】The full length of dfprl was 1 282 bp, with 639 bp cDNA sequence encoding 212 amino acids, 309 bp 5'-UTR and 334 bp 3'-UTR. The dfprl protein has the typical domain of PRL family, the Hormone_1 domain. dfprl protein is highly similar to PRL protein of other Cichlidae, and the amino acid sequence homology of dfprl with Archocentrus centrarchus prolactin (AcPRL) was the highest (96.70%). The expression level of dfprl in gonad and skin increased gradually after the parent fish entered the rearing stage, and decreased at the end of the rearing stage. The paraffin-fluorescence probe-FISH results showed that dfprl was expressed in skin mucous cells, and it was coincident with the expression site of prolactin receptor (dfprlr) and was highly expressed in the early stage of parental care.【Conclusion】The dfprl gene is highly conserved and has stable Hormone _1 domain. dfprl gene was highly expressed in the skin during the parental care stage, . and the expression sites of dfprl and dfprlr overlapped in skin mucous cells during the parental care stage of discus fish, suggesting that dfprl might be involved in the occurrence of unique parental care behavior of discus fish.

Integrated agriculture-aquaculture has emerged as a promising ecological development model. Crayfish, a popular aquaculture species, are traditionally reared either in monoculture ponds (mono-C) or in rice-crayfish polyculture system (poly-RC). In this study, we introduced a novel polyculture system by combining fruit tree with crayfish (poly-FC), aiming to compare these three crayfish culture modes in terms of production performance and ecological sustainability. The results indicated that crayfish reared in the two polyculture modes exhibited significantly higher specific growth rate and condition factor compared to those in mono-C. Crayfish cultured in poly-FC also showed better muscle quality and higher levels of crude fat and flavor or essential amino acids. Isotope mixing model showed that feed and benthic animals were the primary food sources of crayfish in mono-C, whereas aquatic plants, fruit litter or rice contributed more to those in polyculture modes. For greenhouse gas emissions, poly-FC mode emitted almost no CO2 and N2O even favored negative CH4 emission, while poly-RC and mono-C modes showed positive emissions of CH4 and CO2, respectively. Supported by metagenomics, the sink of CH4 in poly-FC was probably due to the lower mcr abundance but the higher pmo abundance in water. The low production and emission of N2O in poly-FC might result from the low-abundant Nitrospirae_bacterium and its coding gene norC in sediment, consistent with the lower denitrification rate but the higher NO3- concentration than mono-C. Overall, our findings reveal the superiority of polyculture of fruit tree with crayfish in terms of production performance and greenhouse gas emissions in the system.