Genome-wide identification and expression analysis of C-type lectins in discus fish (Symphysodon aequifasciatus) during parental care.

Discus fish (Symphysodon aequifasciatus) exhibit a unique parental care behavior: adult discus produces secretion through their skin, on which the larvae live after birth. The immune components in the skin mucus of parental discus would change during different parental care. C-type lectins (CTLs) could identify and eliminate pathogenic microorganisms and play important roles in innate immunity. Studies on CTLs of discus fish especially during parental care, however, are scarce. Here, we identified 186 CTL genes that distributed in 27 linkage groups based on discus genome. Phylogenetic analysis showed that S. aequifasciatus CTL (SaCTL) members were grouped into 14 subfamilies. A total of 80 gene replication events occurred, of which 15 pairs were subjected to segmental duplication and 65 pairs underwent tandem duplication. Ka/Ks ranged from 0.11 (SaCTL25/SaCTL158) to 0.68 (SaCTL36/SaCTL69), all undergoing purifying selection. RNA-seq analysis revealed that SaCTL members, including duplicated genes, in the skin of parental discus show distinct expression patterns in different care stages and between male and female parents. The SaCTL11 was differentially expressed in most care stages and reached the maximum after eggs spawned, but the expression of its paired SaCTL14 was low in each stage. The SaCTL39 increased first and then decreased, reaching a peak in eggs spawned, while paired SaCTL48 first decreased and then increased, reaching a peak in hatched eggs. The SaCTL50 was differentially expressed only in female fish during care, but not in male fish. These results provide new insights into the evolution and potential functional differentiation of CTLs in discus fish during parental care.

Research progress of microRNA in spinal cord injury.

Spinal cord injury (SCI) is a serious central nervous system disease with high disability and mortality rates and complex pathophysiologic mechanisms. MicroRNA (miRNA), as a kind of non-coding RNA, plays an important role in SCI. miRNA is involved in the regulation of inflammatory response, oxidative stress, axonal regeneration, and apoptosis after SCI, and interacts with long non-coding RNA (lncRNA) and circular RNA (circRNA) to regulate the pathophysiological process of SCI. This paper summarizes the changes in miRNA expression after SCI, and reviews the targeting mechanism of miRNA in SCI and the current research status of miRNA-targeted drugs to provide new targets and new horizons for basic and clinical research on SCI.

Gut microbiota communities of reciprocal hybrids from koi (Cyprinus carpio) and goldfish (Carassius auratus) are more similar to koi than goldfish.

AIMS: To investigate the gut microbiota communities of reciprocal hybrids and inbred lines of koi (Cyprinus carpio) and goldfish (Carassius auratus), as well as the genetic effect of intestinal microbiota between hybrids and parents. METHODS AND RESULTS: The reciprocal hybrids and inbred lines derived from the parents, koi and goldfish, were established. Then, the bacterial 16S rRNA gene of intestinal contents was sequenced using Illumina Miseq PE300. Alpha diversity in the two types of hybrids was lower than inbred lines of koi or goldfish and was highest in goldfish, followed by koi. For beta diversity, microbial samples presented clear clusters and the two types of hybrids were more similar to koi than goldfish, indicating the gut microbiota of the reciprocal hybrids was more affected by koi. The dominant phyla were Proteobacteria, Actinobacteria and Firmicutes in koi, and Proteobacteria, Fusobacteria and Actinobacteria in goldfish, and Proteobacteria, Fusobacteria and Firmicutes in the reciprocal hybrids. In the case of Proteobacteria, the dominant classes were Alphaproteobacteria and Gammaproteobacteria in four fish. The dominant genera were norank_f_Rhizobiales_Incertae_Sedis and Plesiomonas in koi, Cetobacterium in goldfish, and Cetobacterium and ZOR0006 in the reciprocal hybrids. PICRUSt1 predictive function analysis showed that the reciprocal hybrids had lower abundance in the most functional categories than koi and goldfish. CONCLUSIONS: The gut microbiota of reciprocal hybrids was more affected by koi. Two types of hybrids possessed the same dominated phyla and were different from the inbred lines of koi and goldfish. SIGNIFICANCE AND IMPACT OF THE STUDY: It enhanced our understanding of gut microbiota of hybrid lines of goldfish and koi and provided a new perspective for the selective breeding of gut microbiota traits.

Occurrence and Characteristics of Microplastics Contamination in Different Intensive Aquaculture Systems Nearby the Yangtze Estuary, China.

Microplastics (MPs) pollution has been extensively investigated in natural fishery waters, but studies on intensive aquaculture systems are scarce. Here, the occurrence and properties of MPs were investigated and compared between four different aquaculture systems nearby the Yangtze Estuary. The average MPs concentration was in order of recirculating aquaculture system (RAS, 1.67 particles/L) < aquarium (2.47 particles/L) < cement pond (10.09 particles/L) < earthen pond (13.81 particles/L). Compared to fragment MPs, fiber was the more abundant shape in aquarium (85.88%), RAS (77.61%) and earthen pond (68.13%). A total of six colors were found in four systems. The black MPs accounted for 56.86% and 47.45% in aquarium and RAS system, respectively. The high proportion of blue MPs was found in cement pond (37.65%) and earthen pond (40%). The most MPs sizes observed in the four systems were 43% of 50-300 µm MPs in aquarium; 44% and 30.19% of 300-1000 µm MPs in RAS and cement pond, respectively; and 30.19% of 3000-5000 µm MPs in earthen pond. For polymers, polypropylene occupied 47.83% in aquarium and RAS, 41.46% in cement pond and 27.79% in earthen pond. Proportion of rayon was highest in RAS (60.87%) and 34.04% of nylon was found in earthen pond. These results could provide scientific reference for further traceability and removal of MPs in different aquaculture systems.

Brain transcriptome analysis reveals genes involved in parental care behaviour in discus fish (Symphysodon haraldi).

Parental care is common in mammals and allows offspring to obtain milk, a substance rich in a range of nutritional and non-nutritional factors crucial to the survival of newborns. The discus fish Symphysodon spp., an Amazonian cichlid, shows an unusual behaviour: Free-swimming fry bite on their parents' skin mucus for growth and development during the first month after hatching. This is similar to the breastfeeding behaviour of mammals, but little is known about the regulatory mechanism by which discus secrete 'milk' and the related genes involved in parental care. Here, transcriptome sequencing was performed by using the brain tissues of female discus fish in parental and non-parental care. The results showed that a total of 86 differentially expressed genes (71 up-regulated genes and 15 down-regulated genes) were obtained by comparing parental with non-parental discus fish, including up-regulated LAPTM, FOXB, SOX1S, OTX2 and NR1F2, and down-regulated EDNRB, PRKCD, H1-5 and HBE. Through functional enrichment analysis, a total of 20 pathways were identified, e.g., estrogen signaling pathway, inflammatory mediator regulation of TRP channels, vascular smooth muscle contraction, GnRH signaling pathway, neurotrophin signaling pathway, NOD-like receptor signaling pathway, Jak-STAT signaling pathway, Fc gamma R-mediated phagocytosis, serotonergic synapse, autophagy-animal and cytokine-cytokine receptor interaction. These pathways and related genes might play important roles in the regulation of discus 'milk' secretion.

[Optimization of isolation and culture of Lin- Sca-1+ cardiac stem cells from newborn mice].

Cardiac stem cells (CSCs) transplantation has been recognized to be effective on the treatment of myocardial infarction (MI), but some techniques still need to be developed in the isolation and culture of CSCs, which is the key problem restricting the clinical application of CSCs. This study was focused on the isolation of Lin- (lineage-negative) Sca-1+ (stem cell antigen-1-positive) CSCs from newborn C57BL/6J mice (0-3 d) by mixed enzymatic-explant isolation in combination with immunomagnetic separation. The digesting time, digesting frequency, incubation temperature, stirring speed, centrifugation time and rotational speed were strictly controlled in the experiment. In order to increase the survival rate of CSCs, the medium changing time and manner were optimized in primary CSCs culture. The percentages of Sca-1+ cells in primary and passage cells were detected by flow cytometry and immunofluorescence staining. The results showed that: (1) the proportion of Lin- Sca-1+ cells within the collected cells could be as high as (85.03 ± 5.60)% after isolation and purification; (2) In vitro culture of Lin- Sca-1+ CSCs grew into spheres on the 5th day, and over the whole bottom of the dish on the 7th day. The growth curve showed that the cells were in logarithmic growth phase on the 3rd day; (3) Immunofluorescence staining data showed that the expression of Sca-1, the CSCs membrane-specific marker, was decreased after subculture, and flow cytometry data showed that the percentages of Sca-1+ cells were (71.82 ± 2.63)%, (58.38 ± 3.70)% and (46.19 ± 4.72)% in passage 1 (P1), P3, and P5 CSCs, respectively. The above results suggest that high purity of Lin- Sca-1+ CSCs can be obtained by enzymolysis combined with immunomagnetic separation method. Moreover, the CSCs culture system is stable. In our experiment, the Sca-1+ CSCs isolation and culture method has been successfully established, and it is simple, stable, effective and reliable. The method can provide a stable methodological basis for the treatment of MI by Lin- Sca-1+ CSCs transplantation.

Proteomic analysis revealed gender-related differences in the skin mucus proteome of discus fish (Symphysodon haraldi) during the parental and non-parental care periods.

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.

Comprehensive assessment of three crayfish culture modes: From production performance to environmental sustainability.

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.

Reshaping the plastisphere upon deposition: Promote N2O production through affecting sediment microbial communities in aquaculture pond.

Microplastics (MPs) could provide vector for microorganisms to form biofilm (plastisphere), but the shaping process of MPs biofilm and its effects on the structure and function of sedimentary microbial communities especially in aquaculture environments are not reported. For this, we incubated MPs biofilm in situ in an aquaculture pond and established a sediment microcosm with plastisphere. We found that the formation of MPs biofilm in surface water was basically stable after 30 d incubation, but the biofilm communities were reshaped after deposition for another 30 d, because they were more similar to plastisphere communities incubated directly within sediment but not surface water. Moreover, microbial communities of MPs-contaminated sediment were altered, which was mainly driven by the biofilm communities present on MPs, because they but not sediment communities in proximity to MPs had a more pronounced separation from the control sediment communities. In the presence of MPs, increased sediment nitrification, denitrification and N2O production rates were observed. The K00371 (NO2-⇋NO3-) pathway and elevated abundance of nxrB and narH genes were screened by metagenomic analysis. Based on structural equation model, two key bacteria (Alphaproteobacteria bacterium and Rhodobacteraceae bacterium) associated with N2O production were further identified. Overall, the settling of MPs could reshape the original biofilm and promote N2O production by selectively elevating sedimental microorganisms and functional genes in aquaculture pond.

Characteristics and risks of microplastic contamination in aquaculture ponds near the Yangtze Estuary, China.

Microplastic pollution has been frequently reported in natural water environments, but studies on the occurrence and characteristics of microplastic in aquaculture environments especially in pond production system are relatively scarce. Herein, we investigated the abundance and characteristics of microplastic pollution in aquaculture ponds that farm different species (fish, prawn and crab) near the Yangtze Estuary, China. The average abundance of microplastic in pond water and sediment was 36.25 ± 6.79 items/L and 271.65 ± 164.83 items/kg, respectively. Compared to fish ponds (208.43 ± 57.82 items/kg), microplastic abundance was significantly higher in sediment of crab and prawn ponds (312.02 ± 38.76 and 248.87 ± 36.51 items/kg respectively). Across all ponds, transparent, white and black microplastic were the common colors. Fiber was the most common type, accounting for 40.9% and 58.6% in pond water and sediment, respectively. The size of microplastic was mainly distributed between 300 and 1000 µm. For microplastic polymer composition, polyethylene (PE) was predominant in pond water, accounting for 55%, followed by polyamide with 15%. The predominant polymer in sediment was PE with 34%, followed by polypropylene with 18%. As for the ecological risk assessment of microplastic, the pollution load index was 7.6 (risk level I) and 8.9 (risk level I) for pond water and sediment, respectively. The polymer hazard index was 85.3 (risk level II) and 12.1 (risk level II) for pond water and sediment, respectively. Taken together, the pollution risk index was rated as high and very high for pond sediment and water, respectively. These results provide a basis for the comprehensive evaluation and developing practical approaches to deal with microplastic in aquaculture pond, which is of great significance to the healthy development of pond aquaculture.

Cloning, molecular characterization, and expression analysis of the signal transducer and activator of transcription 3 (STAT3) gene from grass carp (Ctenopharyngodon idellus).

Signal transducer and activator of transcription 3 (STAT3) binds to Janus kinase 2 (JAK2) to initiate the JAK2/STAT3 signal transduction pathway, which plays an important role in cancer cell proliferation, immune regulation, reproduction, lipid metabolism, and other physiological processes of the organism. In this study, the cDNA sequence of the STAT3 gene from grass carp was cloned using RACE (rapid-amplification of cDNA ends). Twelve characteristics of the STAT3 gene and its encoded protein sequence were predicted and analyzed using bioinformatics methods; these features included the general physical and chemical properties, the hydrophobicity, the secondary structure and the three-dimensional structure of the protein. Quantitative real-time PCR was employed to detect grass carp STAT3 expression pattern in different tissues. The results showed that the full-length STAT3 gene from grass carp is 2739-bp long and contains a 216-bp 5'UTR, a 300-bp 3'UTR, and a 2223-bp open reading frame (ORF) that encodes a 740-amino acid peptide. The deduced protein exhibited 99%∼94% homology to the STAT3 protein of zebrafish (Danio rerio), medaka (Oryzias latipes), turbot (Scophthalmus maximus), white-spotted char (Salvelinus leucomaenis), mandarin fish (Siniperca chuatsi), rainbow trout (Oncorhynchus mykiss), and green pufferfish (Tetraodon fluviatilis). The deduced grass carp STAT3 protein contains a protein interaction domain, an alpha domain, a DNA binding domain, and an SH2 domain. The STAT3 protein of grass carp is a hydrophilic and non-secretory protein, and its molecular mass and isoeletronic point were found to be 98,5412.1 Da and 6.39, respectively. The structural elements of STAT3 included α-helixes, ß-sheets, and loops. The grass carp STAT3 is expressed in all of the six tissues tested, which were the liver, spleen, gill, muscle, heart, and brain. The highest expression level was found in the liver (P < 0.05), whereas a significantly lower expression level was found in the spleen, gills, brain, and muscle (P < 0.05), and the lowest expression level was found in the heart (P < 0.05). This study provides a basis for further structural and functional exploration of the STAT3 from grass carp, including its deduced protein and its signal transduction function.

Astaxanthin mitigates oxidative stress caused by microplastics at the expense of reduced skin pigmentation in discus fish.

Microplastics (MPs) exposure generally triggers oxidative stress in fish species and vertebrate pigmentation is commonly influenced by oxidative stress, but MPs-induced oxidative stress on fish pigmentation and body color phenotype has not been reported. The aim of this study is to determine whether astaxanthin could mitigate the oxidative stress caused by MPs but at the expense of reduced skin pigmentation in fish. Here, we induced oxidative stress in discus fish (red skin color) by 40 or 400 items/L MPs under both astaxanthin (ASX) deprivation and supplementation. We found that lightness (L*) and redness (a*) values of fish skin were significantly inhibited by MPs under ASX deprivation. Moreover, MPs exposure significantly reduced ASX deposition in fish skin. The total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activity in fish liver and skin were both significantly increased with the increase of MPs concentration, but content of glutathione (GSH) in fish skin showed a significant decrease. For ASX supplementation, the L*, a* values and ASX deposition were significantly improved by ASX, including the skin of MPs-exposed fish. The T-AOC and SOD levels changed non-significantly in fish liver and skin under the interaction of MPs and ASX, but ASX significantly reduced GSH content in fish liver. Biomarker response index indicated that ASX could improve the moderately altered antioxidant defense status of MPs-exposed fish. This study suggests that the oxidative stress caused by MPs was mitigated by ASX but at expense of reduced fish skin pigmentation.

Microplastics inhibit biofloc formation and alter microbial community composition and nitrogen transformation function in aquaculture.

Biofloc technology, extensively used in intensive aquaculture systems, can prompt the formation of microbial aggregates. Microplastics (MPs) are detected abundantly in aquaculture waters. This study explored the effects of MPs on biofloc formation, microbial community composition and nitrogen transformation function in simulated biofloc aquaculture production systems. The formation process and settling performance of bioflocs were examined. High-throughput sequencing of 16S and 18S rRNA genes was used to investigate the microbial community compositions of bioflocs. Nitrogen dynamics were monitored and further explained from functional genes and microorganisms related to nitrogen transformation by metagenome sequencing. We found that the aggregates consisting of bioflocs and MPs were formed and the systems with MPs had relatively weak settling performance. No significant differences in bacterial diversity (p > 0.05) but significant differences in eukaryotic diversity (p < 0.05) were found between systems without and with MPs. Significant separations in the microbial communities of prokaryotes (p = 0.01) and eukaryotes (p = 0.01) between systems without and with MPs were observed. The peak concentration of nitrite nitrogen (NO2--N) in systems with MPs was lower than that in systems without MPs (pControl/MPs Low = 0.02 and pControl/MPs High = 0.03), probably due to the low abundance of hao and affiliated Alphaproteobacteria_bacterium_HGW-Alphaproteobacteria-1 and Alphaproteobacteria_bacterium, but the high abundance of nxrA and affiliated Alphaproteobacteria_bacterium_SYSU_XM001 and Hydrogenophaga_pseudoflava that related to nitrification. The low concentration of NO2--N in systems with MPs suggested that the presence of MPs might inhibit ammonia oxidation but promote nitrite oxidation by altering the microbial community structure and function. These results indicated that aggregates consisting of bioflocs and MPs could be formed in aquaculture water, and thus, inhibiting their settlement and altering nitrogen transformation function by affecting the microbial community composition.

Genome-wide identification and skin expression of immunoglobulin superfamily in discus fish (Symphysodon aequifasciatus) reveal common genes associated with vertebrate lactation.

Discus Symphysodon spp. employs an unusual parental care behavior where fry feed on parental skin mucus after hatching. Studies on discus immunoglobulin superfamily (IgSF) especially during parental care are scarce. Here, a total of 518 IgSF members were identified based on discus genome and clustered into 12 groups, unevenly distributing on 30 linkage groups. A total of 92 pairs of tandem duplication and 40 pairs of segmental duplication that underwent purifying selection were identified. IgSF genes expressed differentially in discus skin during different care stages and between male and female parents. Specifically, the transcription of btn1a1, similar with mammalian lactation, increased after spawning, reached a peak when fry started biting on parents' skin mucus, and then decreased. The expression of btn2a1 and other immune members, e.g., nect4, fcl5 and cd22, were up-regulated when fry stopped biting on mucus. These results suggest the expression differentiation of IgSF genes in skin of discus fish during parental care.

Distinct skin morphological and transcriptomic profiles between wild and albino Oscar Astronotus ocellatus.

Oscar Astronotus ocellatus is an important ornamental fish, including albino and wild varieties. Albino individuals attract aquarium hobbyists due to their unique body color, but studies on the species' albinism mechanism are currently scarce. Here, we investigated the morphological and transcriptomic profiles of the skin of albino and wild Oscar. The results showed that the albino type had fewer oval-shaped melanophores and immature melanosomes but that the wild type contained more stellate-shaped melanophores and mature melanosomes. Albino Oscar had a degenerative pigment layer without obvious melanin deposition and content, while the wild type contained more concentrated melanin within the pigment layer. A total of 272,392 unigenes were detected, 109 of which were identified as differentially expressed genes (DEGs) between albino and wild Oscar. Pathways of DEGs, including those involved in complement and coagulation cascades, novobiocin biosynthesis, Th1 and Th2 cell differentiation, and tropane, piperidine and pyridine alkaloid biosynthesis, were significantly enriched. DEGs, including upregulated Sfrp5 and Tat, and downregulated Wnt-10a, Ppp3c, Notch1 and Trim27 involved in the Wnt signaling pathway, Notch signaling pathway, tyrosine metabolism, MAPK signaling pathway and melanogenesis, might be associated with the albinism of Oscar. This study characterized the difference in melanophore morphology between wild and albino Oscar and identified some albinism-related candidate genes and signaling pathways, helping to understand the genetic mechanism of fish albinism.

Microplastics drive nitrification by enriching functional microorganisms in aquaculture pond waters.

The plastisphere refers to biofilm formation on the microplastic (MP) surface, but its subsequent functions, especially driving the nitrogen biogeochemical cycle, are rarely studied. Here, MPs were incubated in the pelagic water and benthic water-sediment interface of an aquaculture pond, and the two corresponding microcosms amended with incubated plastisphere were simulated. The results showed decreased ammonia concentrations and increased nitrification rates in microcosms with either pelagic or benthic plastispheres. To uncover the possible mechanisms, the community structure and function of the plastisphere were investigated. As clarified by 16S rRNA, the community diversity of the pelagic plastisphere was significantly higher than that of the corresponding hydrosphere. Plastisphere communities, especially those incubated in pelagic water, were separated from the hydrosphere. Moreover, the abundance of Proteobacteria increased while the abundance of Cyanobacteria decreased in both plastispheres. Metagenome further revealed that the abundance of amoA and annotated Nitrososphaeraceae_archaeon and hao and affiliated Nitrosomonas_europaea, which contributed to ammonia oxidation to nitrite, was higher in the benthic plastisphere. Comparing the pelagic plastisphere with the corresponding hydrosphere, however, the abundance of nxrA and annotated Nitrobacter hamburgensis and nxrB and the affiliated Nitrospira moscoviensis, which are involved in nitrite oxidation, was more abundant in the plastisphere. These findings suggest that the plastisphere might selectively enrich functional microorganisms and genes in a habitat-dependent manner to promote nitrification in aquaculture ponds.

Micro/nano-plastics cause neurobehavioral toxicity in discus fish (Symphysodon aequifasciatus): Insight from brain-gut-microbiota axis.

Numerous studies have investigated neurobehavioral toxicity of microplastics, but no studies have illustrated mechanism via brain-gut axis. Here, juvenile discus fish (Symphysodon aequifasciatus) were exposed for 96 h to microfibers (900 µm, fiber, MFs) or nanoplastics (~88 nm, bead, NPs) with three concentrations (0, 20 and 200 µg/L). Accumulation in fish gut was independent of plastics type and concentration. MFs reduced growth performance while NPs weakened swimming and predatory performance of post-exposed discus. For brain cholinesterase activity, acetylcholinesterase was activated by NPs while NPs/MFs exposure inhibited butyrylcholinesterase. Concentrations of neurotransmitters (acetylcholine, dopamine and γ-aminobutyric acid) increased in brain but decreased in gut after NPs or MFs exposure. For gut microbiota, increased richness under MFs exposure was observed. At phylum level, Proteobacteria proportion was lower in NPs but higher in MFs. Abundance of Clostridia and Fusobacteriia (Bacillus), potentially secreting neurotransmitters, increased in NPs but decreased in MFs. Brain transcriptomics revealed seven upregulated and four downregulated genes concerning neural-activities. Pathways of neuroactive ligand-receptor interaction and serotonergic synapse were enriched in both MFs and NPs, but dopaminergic synapse pathway was enriched only in MFs. These results established a novel mechanism by which microplastics might cause behavioral toxicities via brain-gut-microbiota axis.

Microplastics: A tissue-specific threat to microbial community and biomarkers of discus fish (Symphysodon aequifasciatus).

As detriments in aquatic environments, microplastics (MPs) have been commonly studied on organisms, but tissue-scale effects of MPs were poorly understood. Discus fish (Symphysodon aequifasciatus), herewith, were exposed to polystyrene MPs (0/20/200 µg/L) for 28 d. We found that MPs significantly inhibited growth performance. MPs were observed in skin, gill and intestine after 14/28-d exposure. MPs bioaccumulation was independent of exposure time, but increased with MPs concentrations. Microbial community diversity of fish gill, but not skin and intestine, in MPs treatments was significantly increased. Bacterial community of MP-treated skin and gill were obviously separated from control. Skin dominant phyla changed from Actinobacteriota to Proteobacteria and Firmicutes. Proteobacteria gradually occupied dominance in gill after exposure. Furthermore, MPs-induced skin oxidative stress was demonstrated by the activation of superoxide dismutase and catalase. Skin malondialdehyde also increased and showed significant correlations with four bacterial phyla, e.g., Proteobacteria. Gill Na+/K+-ATPase activity decreased, strongly correlating to microbial community changes caused by MPs. Intestinal digestive enzymes activity (pepsin, lipase and α-amylase) reduced, revealing correlation with bacterial community especially Fibrobacterota. These results suggest a tissue-specific effect of MPs to microbial community and biomarkers in aquatic organism.

Ecological stoichiometric and stable isotopic responses to microplastics are modified by food conditions in koi carp.

Microplastics (MPs) can be easily taken up by a wide range of aquatic animals and cause blockage of the digestive tract leading to starvation. Meanwhile, aquatic organisms are facing threats posed by food restriction in both wild and cultured environment. Little knowledge, however, exists on how MPs interact with food conditions to affect aquatic animals. Here, koi carp were exposed to polystyrene MPs (0, 100 or 1000 µg/L) under controlled feeding (satiated or starved) for 30 or 60 days. MPs reduced and interacted synergistically with food conditions on growth after 30 days but antagonistically after 60 days. MPs reduced crude lipid and carbohydrate but increased and antagonistically interacted with feeding conditions on crude protein. Food conditions interacted with MPs on C, N and P but stoichiometric responses were decoupled with macromolecules changes. Food conditions antagonistically interacted with MPs on δ13C after 60 days. Linear discriminant analysis revealed that C:P and N:P were the two most important measured parameters accounting for the response of koi towards MPs and food restriction, presenting an antagonistic interaction of MPs and food status with the prolonged exposure duration.

Comparative metabolomics analysis of pigmentary and structural coloration in discus fish (Symphysodon haraldi).

Discus fish have a variety of body colors including pigmentary and structural colors, studies on specific substances and related metabolic pathways associated with body coloration, however, are scarce to the present. Here, we used single-color (blue, yellow and white) of discus for comparative metabolomics analysis of pigmentary and structural coloration. Statistical model showed significant separations between three colors of discus, suggesting the distinct metabolite profiles of discus pigmentary and structural colors. More astaxanthin was found in yellow discus, which might be the cause of yellow pigmentary color. Moreover, docosahexaenoic acid, arachidonic acid, linoleic acid, eicosapentaenoic acid, 1-stearoyl-2-oleoyl-sn-glycerol 3-phosphocholine, dodecanoic acid and myristic acid related to lipid metabolism and pathways of ABC transporters and biosynthesis of unsaturated fatty acids were more enriched in yellow discus. More adenine, xanthine and hypoxanthine were enriched in blue discus, which might account for the blue structural color. Moreover, amino acids associated with purine biosynthesis, e.g., L-alanine and L-isoleucine, were reduced but pathways of protein digestion and absorption, aminoacyl-tRNA biosynthesis, purine metabolism and glycine, serine and threonine metabolism were enriched in blue discus. Overall, these results reveal specific chromophores and related metabolic pathways involved in pigmentary and structural coloration of discus fish. SIGNIFICANCE: We detected specific chromophores present in skin of pigmentary and structural colors of discus and revealed potential metabolic pathways associated with body coloration. These results contribute to our understanding of the mechanism of body color formation in discus fish.