Response mechanism of gut microbiome and metabolism of European seabass (Dicentrarchus labrax) to temperature stress

Impacts of polystyrene nanoplastics on zebrafish gut microbiota and mechanistic insights

Aquatic environments are frequently contaminated with nanoplastics (NPs) ranging from 1-100 nm generated by plastic aging, but their bio-enrichment and toxicological impacts remain poorly understood. This study investigates how chronic exposure to carboxylated polystyrene nanoplastics (PNPs) alters gut microbiota composition and function in zebrafish (Danio rerio). Adult zebrafish were exposed to 50 nm PNPs at concentrations of 0.1, 1.0, and 10 mg/L for 14 and 28 days, followed by gut microbiota analysis using 16S rRNA gene sequencing. PNP exposure altered gut microbiota composition, including an increase in Proteobacteria abundance and a decrease in Firmicutes, Bacteroidetes, and the inflammation-related genus Alistipes. Beneficial probiotics such as Faecalibacterium, Streptococcus, Bifidobacterium, and Lachnospira were diminished, while pathogenic bacteria proliferated. TEM imaging revealed the internalization of PNP particles within intestinal tissues resulted in vacuolation, suggesting potential epithelial damage. Co-occurrence network patterns of gut microbiota greatly decreased during treatment with NPs. The neutral community model showed that among PNP treatments, 0.1 mg/L led to a less predictable (stochastic assembly process). PNP exposure led to increased predicted microbial functions (via PICRUSt2) related to xenobiotic metabolism, infection pathways, and lipopolysaccharide (LPS) production, while RNA transport and N-glycan biosynthesis were decreased. However, pathways related to microbial antioxidants exhibited significant variation across different PNP levels. These results provide critical insights into the toxicological impacts of chronic PNP exposure on fish gut health, highlighting the potential risks to aquatic ecosystems and human health.

Integration of histopathology, transcriptomics and non-targeted metabolomics reveals toxic effects of thiamethoxam under acute stress in mirror carp (Cyprinus carpio var. Longke-11 mirror)

In recent years, the increasing application of thiamethoxam (THM), coupled with its high leaching and solubility in water, has led to growing concerns regarding THM residues in aquatic environments, which may pose toxic effects on aquatic organisms, particularly fish. However, the toxicological mechanisms of THM in freshwater fish remain unclear. In this study, using histopathology, transcriptomics, and non-targeted metabolomics, the toxic effects of different concentrations of THM under acute stress (96 h) were investigated in mirror carp (Cyprinus carpio var. Longke-11 mirror). The results showed that under acute THM stress, liver tissues of the mirror carp exhibited vacuolation, cellular degeneration, and enhanced cytoplasmic eosinophilia, while gill tissues displayed epithelial structure loss, epithelial cell detachment, degeneration, and vacuolation, with the severity of lesions increasing with exposure concentration. Transcriptomic analysis revealed that the number of differentially expressed genes (DEGs) increased with the concentration of THM. Genes related to immune response and antioxidant stress were mostly downregulated, while genes related to inflammation and apoptosis were predominantly upregulated. The downregulation of common DEGs (SLC7A11, ITLN, CDH17) further confirmed these results. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed significant enrichment in pathways related to inflammation and oxidative stress, with the NF-kappa B signaling pathway identified as the key pathway affected. Metabolomic analysis showed that differentially expressed metabolites (SCMs) associated with amino acid and lipid metabolism were significantly downregulated. The downregulation of SCM acetylcysteine further affected the antioxidant capacity of mirror carp. Moreover, different concentrations of THM affected phenylalanine metabolism, cysteine and methionine metabolism, and biosynthesis of unsaturated fatty acids in the liver of mirror carp. Integrated analysis of apoptosis-related factors (TP53INP1, PRF1, Sphingosine) upregulation and anti-apoptotic factors (Bcl2l1) downregulation suggested that THM induces apoptosis in mirror carp cells. These results indicate that THM stress affects the immune system, amino acid, and lipid metabolism in mirror carp, leading to inflammation, oxidative stress, and apoptosis. This study provides preliminary insights into the toxic mechanisms of THM in fish and can serve as a scientific basis for THM risk assessment and environmental protection.

Effect of microcystin-LR on intestinal microbiota, metabolism, and health of zebrafish (Danio rerio)

Microcystin-LR (MC-LR) is typically produced along with the occurrence of cyanobacterial blooms, potentially exerting deleterious effects on intestinal microbiota and health in aquatic animals. To date, the underlying mechanism by which MC-LR affects intestinal health remains elusive. In this study, adult male zebrafish were exposed to MC-LR to assess its impact on the microbiome and metabolome. Histopathological and biochemical results indicated that MC-LR damaged intestinal villi and epithelial cells, induced intestinal barrier injury and inflammatory response. Metabolomics results revealed that MC-LR induced amino acid, carbohydrate, lipid, energy metabolisms dysbiosis, and specifically promoted glycine, serine and threonine metabolism. Metagenomics results demonstrated that MC-LR altered the composition of intestinal microbiota, and microbial function prediction suggested that MC-LR promoted the functions associated with amino acid, lipid, carbohydrate and energy metabolisms. Multiomics and Metorigin analyses jointly confirmed that glycine, serine and threonine metabolism was predominantly regulated by dominant Proteobacteria, Firmicutes, Fusobacteriota and Bacteroidota under MC-LR stress. This study offers a comprehensive perspective on the toxicity of microbiota and microbiota-derived metabolism in fish intestines induced by MC-LR and deepens our comprehension of the disruptive influence of MC-LR on intestinal homeostasis in organisms.

Alterations and resilience of intestinal microbiota to increased water temperature are accompanied by the recovery of immune function in Nile tilapia

In the context of ongoing global warming, fish, as aquatic ectotherms, are highly vulnerable to increased water temperature caused by climate change and extreme heatwaves because of their inability to maintain their body temperature. After prolonged coevolution, the intestinal microbiota has become an integral part of fish and plays a pivotal role in immunity and metabolism. To date, however, little is known about the effects of increased water temperature on the intestinal microbiota of fish, particularly the intestinal mucosa-associated microbiota. Here, we investigated the variation patterns of the intestinal microbiota and immune status in Nile tilapia (Oreochromis niloticus; 125.02 ± 4.55 g) under increased water temperature. The results showed that the microbial diversity, structure, dominant microbes, and predicted function of fish intestinal microbiota were resilient to low-level warming (increasing by 2 °C) but not to high-level warming (increasing by 8 °C) and that fish immune parameters (serum lysozyme content and bactericidal activity) recovered simultaneously. Notably, along with compromised immune function, short-term warming (7 days) drove a significant increase in the microbial richness and diversity of fish intestinal mucosae, in which the overgrowth of opportunistic pathogens such as Romboutsia ilealis, Escherichia-Shigella, Fusobacterium, Streptococcus, Acinetobacter, and Enterobacter inhibited the colonization of potential probiotics such as Cetobacterium, ultimately resulting in a significant reduction in metabolic pathways and a significant increase in the potentially pathogenic phenotype. After long-term warming (37 days), the above alterations disappeared in low-level warming but remained in high-level warming. Critically, long-term warming disrupted the network complexity and stability of the intestinal mucosa- and digesta-associated microbiota to different extents. Collectively, this study revealed that the alterations and resilience of intestinal microbiota to increased water temperature coincided with the recovery of immune function in fish. Our findings extend the understanding of how the intestinal microbiota in aquatic ectotherms respond to increased water temperature, providing important implications for harnessing the potential benefits of host-associated microorganisms to enhance their resilience to climate change.

Fish gut-derived probiotic Pediococcus pentosaceus alleviates gossypol-induced intestinal inflammation by inhibiting NLRC3/NF-κB/IL-1β signal pathway in Nile tilapia

Cottonseed meal (CSM) and cottonseed protein concentrate (CPC) serve as protein alternatives to fish meal and soybean meal in the feed industry. However, the presence of gossypol residue in CSM and CPC can potentially trigger severe intestinal inflammation, thereby restricting the widespread utilization of these two protein sources. Probiotics are widely used to prevent or alleviate intestinal inflammation, but their efficacy in protecting fish against gossypol-induced enteritis remains uncertain. Here, the protective effect of Pediococcus pentosaceus, a strain isolated from the gut of Nile tilapia (Oreochromis niloticus), was evaluated. Three diets, control diet (CON), gossypol diet (GOS) and GOS supplemented with P. pentosaceus YC diet (GP), were used to feed Nile tilapia for 10 weeks. After the feeding trial, P. pentosaceus YC reduced the activity of myeloperoxidase (MPO) in the proximal intestine (PI) and distal intestine (DI). Following a 7-day exposure to Aeromonas hydrophila, the addition of P. pentosaceus YC was found to increase the survival rate of the fish. P. pentosaceus YC significantly inhibited the oxidative stress caused by gossypol, which was evidenced by lower reactive oxygen species (ROS) and malondialdehyde (MDA), as well as higher activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) in PI and DI. Addition of P. pentosaceus YC significantly inhibited enteritis, with the lower expression of pro-inflammatory cytokines (il-1β, il-6, il-8) and higher expression of anti-inflammatory cytokines tgf-β. RNA-seq analysis indicated that P. pentosaceus YC supplementation significantly inhibited nlrc3 and promoted nf-κb expression in PI and DI, and the siRNA interference experiment in vivo demonstrated that intestinal inflammation was mediated by NLRC3/NF-κB/IL-1β signaling pathway. Fecal bacteria transplantation experiment demonstrated that gut microbiota mediated the protective effect of P. pentosaceus YC. These findings offer valuable insights into the application of P. pentosaceus YC for alleviating gossypol-induced intestinal inflammation in fish.

Long-term thermal acclimation enhances heat resistance of Hong Kong catfish (Clarias fuscus) by modulating gill tissue structure, antioxidant capacity and immune metabolic pathways

The rapid temperature changes caused by global warming significantly challenge fish survival by affecting various biological processes. Fish generally mitigate stress through physiological plasticity, but when temperature changes exceed their tolerance limits, even adaptable species like Siluriformes can experience internal disruptions. This study investigates the effects of extreme thermal climate on Hong Kong catfish (Clarias fuscus), native to tropical and subtropical regions. C. fuscus were exposed to normal temperature (NT, 26 ℃) or high temperature (HT, 34 ℃) condition for 90 days. Subsequently, histological, biochemical, and transcriptomic changes in gill tissue were observed after exposure to acute high temperatures (34 ℃) and subsequent temperature recovery (26 ℃). Histological analysis revealed that C. fuscus in the HT group exhibited less impact from sudden temperature shifts compared to the NT group, as they adapted by reducing the interlamellar cell mass (ILCM) and lamellae thickness (LT) of gill tissue, thereby mitigating the aftermath of acute heat shock. Biochemical analysis showed that catalase (CAT) activity in the high temperature group continued to increase, while malondialdehyde (MDA) levels decreased, suggesting establishment of a new oxidative balance and enhanced environmental adaptability. Transcriptome analysis identified 520 and 463 differentially expressed genes in the NT and HT groups, respectively, in response to acute temperature changes. Enrichment analysis highlighted that in response to acute temperature changes, the NT group inhibited apoptosis and ferroptosis by regulating the activity of alox12, gclc, and hmox1a, thereby attenuating the adverse effects of heat stress. Conversely, the HT group increased the activity of pfkma and pkma to provide sufficient energy for tissue repair. The higher degree of heat shock protein (Hsp) response in NT group also indicated more severe heat stress injury. These findings demonstrate alterations in gill tissue structure, regulation of oxidative balance, and the response of immune metabolic pathways to acute temperature fluctuations in C. fuscus following thermal exposure, suggesting potential avenues for further exploration into the thermal tolerance plasticity of fish adapting to global warming.

Optimization and Detection of Freshness Biomarkers of Atlantic Salmon Subjected to Different Vacuum Packaging Conditions during Storage at 0 °C by Metabolomics and Molecular Docking

The freshness of Atlantic salmon is influenced mainly by tissue metabolism, which in turn is affected by storage time and conditions. The alterations in taste profiles and nutritional values of salmon when packaged using vacuum methods have not been fully understood, and the factors contributing to these changes require further research. In this work, the extraction method for flavor nutrients from salmon was optimized via the Plackett-Burman (PB) test. A sensitive and rapid targeted metabolomics method for the simultaneous determination of 34 nutrients was successfully established via ultra-performance liquid chromatography-triple quadrupole/linear ion trap composite mass spectrometry (UHPLC-QTRAP/MS), and various nutritional compositions during storage at 0 °C under different vacuum conditions (0 kPa or -90 kPa) for 4 and 8 days were analyzed. Results showed that storage time had a significant effect on salmon metabolism. The total amino acids decreased by 62.95% and 65.89% at 0 kPa and -90 kPa, respectively. Notably, a marked reduction in histidine after 8 days at -90 kPa may have diminished bitterness, while decreased levels of umami-tasting amino acids like glutamine and aspartic acid affected the overall flavor profile. Overall, the packaging conditions at 0 °C and 0 kPa were more suitable for the preservation of most nutrients in salmon. Pathway enrichment analysis revealed that the reduction in substances was mainly related to the alanine, aspartate, and glutamate metabolism pathways. Alanine, inosine, and histidine, whose levels changed significantly, can bind to the typical umami taste receptor TIR1/TIR3 and can be biomarkers to monitor and determine the freshness or spoilage of salmon after 4-8 days of storage. This study revealed the changes in small-molecule nutrients in salmon during storage under different packaging conditions, which provides a reference for the packaging preservation technology of fresh salmon and new ideas for the evaluation of salmon quality and determination of freshness.

Parabacteroides distasonis regulates the infectivity and pathogenicity of SVCV at different water temperatures

BACKGROUND

Spring viremia of carp virus (SVCV) infects a wide range of fish species and causes high mortality rates in aquaculture. This viral infection is characterized by seasonal outbreaks that are temperature-dependent. However, the specific mechanism behind temperature-dependent SVCV infectivity and pathogenicity remains unclear. Given the high sensitivity of the composition of intestinal microbiota to temperature changes, it would be interesting to investigate if the intestinal microbiota of fish could play a role in modulating the infectivity of SVCV at different temperatures.

RESULTS

Our study found that significantly higher infectivity and pathogenicity of SVCV infection in zebrafish occurred at relatively lower temperature. Comparative analysis of the intestinal microbiota in zebrafish exposed to high- and low-temperature conditions revealed that temperature influenced the abundance and diversity of the intestinal microbiota in zebrafish. A significantly higher abundance of Parabacteroides distasonis and its metabolite secondary bile acid (deoxycholic acid, DCA) was detected in the intestine of zebrafish exposed to high temperature. Both colonization of Parabacteroides distasonis and feeding of DCA to zebrafish at low temperature significantly reduced the mortality caused by SVCV. An in vitro assay demonstrated that DCA could inhibit the assembly and release of SVCV. Notably, DCA also showed an inhibitory effect on the infectious hematopoietic necrosis virus, another Rhabdoviridae member known to be more infectious at low temperature.

CONCLUSIONS

This study provides evidence that temperature can be an important factor to influence the composition of intestinal microbiota in zebrafish, consequently impacting the infectivity and pathogenicity of SVCV. The findings highlight the enrichment of Parabacteroides distasonis and its derivative, DCA, in the intestines of zebrafish raised at high temperature, and they possess an important role in preventing the infection of SVCV and other Rhabdoviridae members in host fish. Video Abstract.

Effects of titanium dioxide nanoparticle exposure on the gut microbiota of pearl oyster (Pinctada fucata martensii)

With the advancement of nanotechnology and the growing utilization of nanomaterials, titanium dioxide (TiO2) has been released into aquatic environments, posing potential ecotoxicological risks to aquatic organisms. In this study, the toxicological effects of TiO2 nanoparticles were investigated on the intestinal health of pearl oyster (Pinctada fucata martensii). The pearl oysters were subjected to a 14-day exposure to 5-mg/L TiO2 nanoparticle, followed by a 7-day recovery period. Subsequently, the intestinal tissues were analyzed using 16S rDNA high-throughput sequencing. The results from LEfSe analysis revealed that TiO2 nanoparticle increased the susceptibility of pearl oysters to potential pathogenic bacteria infections. Additionally, the TiO2 nanoparticles led to alterations in the abundance of microbial communities in the gut of pearl oysters. Notable changes included a decrease in the relative abundance of Phaeobacter and Nautella, and an increase in the Actinobacteria, which could potentially impact the immune function of pearl oysters. The abundance of Firmicutes and Bacteroidetes, as well as the expression of genes related to energy metabolism (AMPK, PK, SCS-1, SCS-2, SCS-3), were down-regulated, suggesting that TiO2 nanoparticles exposure may affect the digestive and energy metabolic functions of pearl oysters. Furthermore, the short-term recovery of seven days did not fully restore these levels to normal. These findings provide crucial insights and serve as an important reference for understanding the toxic effects of TiO2 nanoparticles on bivalves.

Integrated microbiome and metabolome analyses reveal the effects of low pH on intestinal health and homeostasis of crayfish (Procambarus clarkii)

Low pH (LpH) poses a significant challenge to the health, immune response, and growth of aquatic animals worldwide. Crayfish (Procambarus clarkii) is a globally farmed freshwater species with a remarkable adaptability to various environmental stressors. However, the effects of LpH stress on the microbiota and host metabolism in crayfish intestines remain poorly understood. In this study, integrated analyses of antioxidant enzyme activity, histopathological damage, 16S rRNA gene sequencing, and liquid chromatography-mass spectrometry (LC-MS) were performed to investigate the physiology, histopathology, microbiota, and metabolite changes in crayfish intestines exposed to LpH treatment. The results showed that LpH stress induced obvious changes in superoxide dismutase and catalase activities and histopathological alterations in crayfish intestines. Furthermore, 16S rRNA gene sequencing analysis revealed that exposure to LpH caused significant alterations in the diversity and composition of the crayfish intestinal microbiota at the phylum and genus levels. At the genus level, 14 genera including Bacilloplasma, Citrobacter, Shewanella, Vibrio, RsaHf231, Erysipelatoclostridium, Anaerorhabdus, Dysgonomonas, Flavobacterium, Tyzzerella, Brachymonas, Muribaculaceae, Propionivibrio, and Comamonas, exhibited significant differences in their relative abundances. The LC-MS analysis revealed 859 differentially expressed metabolites in crayfish intestines in response to LpH, including 363 and 496 upregulated and downregulated metabolites, respectively. These identified metabolites exhibited significant enrichment in 24 Kyoto Encyclopedia of Genes and Genomes pathways (p < 0.05), including seven and 17 upregulated and downregulated pathways, respectively. These pathways are mainly associated with energy and amino acid metabolism. Correlation analysis revealed a strong correlation between the metabolites and intestinal microbiota of crayfish during LpH treatment. These findings suggest that LpH may induce significant oxidative stress, intestinal tissue damage, disruption of intestinal microbiota homeostasis, and alterations in the metabolism in crayfish. These findings provide valuable insights into how the microbial and metabolic processes of crayfish intestines respond to LpH stress.

Copper exposure causes alteration in the intestinal microbiota and metabolites in Takifugu rubripes

Copper is an environmental pollutant, and copper in aquatic environments mainly comes from soil and water. It enters the environment through atmospheric deposition, sewage discharge, and industrial production, and enters aquatic organisms, causing toxicity. Takifugu rubripes (T. rubripes) is a marine fish with high economic value. Due to the toxic effects of heavy metals on aquatic organisms such as fish, it can affect the gut community and metabolites of fish. The gut is an important channel for fish to communicate with the outside world and a necessary pathway for the metabolism of nutrients and toxic substances in the fish body. Studies have shown that due to changes in global water emissions and the high sensitivity of aquatic organisms to the environment, copper may pose greater potential hazards to aquatic organisms. Copper poses a greater risk to aquatic species than other heavy metals and metal/metal like pollutants (such as cadmium, lead, mercury, arsenic, etc.) . In order to elucidate the effects of copper exposure on the gut of T. rubripes. In this study, we exposed T. rubripes to 0, 50, 100, or 500 μg/L of copper for three days, the effects of copper exposure on the gut microbiota structure and metabolites of the T. rubripes were investigated using 16 S rRNA gene and metabolomics techniques. The research results indicate that with the increase copper concentration, the intestinal tissue of T. rubripes undergoes significant damage. 16 S rRNA sequencing results show that copper exposure alters the structure and metabolites of intestinal microbiota. Copper exposure of 100 and 500 μg/L inhibited the colonization of the bacterial gut, disrupted the intestinal barrier, and made the fish susceptible to the pathogens. Liquid chromatography-mass spectrometry analysis showed that copper regulated the production of metabolites such as L-histidine, arachidonic acid, and L-glutamic acid, which are related to energy and immunity. Microbiome-metabolome correlation analysis showed that Subdoligranulum, Family_XIII_AD3011_group, and Clostridium_sensu_stricto_1 were the key bacteria for copper ion intervention, and they might up-regulate the levels of metabolites such as indole-3-acetic acid, 3-indoleacrylic acid, and 5-hydroxyindole in the tryptophan metabolism pathway. In summary, our research has demonstrated that copper exposure can cause pathological changes in the intestinal tissue of the T. rubripes. High concentrations of copper ions can affect the colonization of the T. rubripes microbiota in the intestine, damage the fish's immune system, and alter the structure and metabolites of the intestinal microbiota, this can lead to intestinal metabolic dysfunction. providing a reference for the evaluation of the biological toxicity effects of heavy metal elements in the marine environment. This study provides a reference for evaluating the biological toxicity effects of heavy metal elements in marine environments.

Microbiome composition and function within the Kellet's whelk perivitelline fluid

Microbiomes have gained significant attention in ecological research, owing to their diverse interactions and essential roles within different organismal ecosystems. Microorganisms, such as bacteria, archaea, and viruses, have profound impact on host health, influencing digestion, metabolism, immune function, tissue development, and behavior. This study investigates the microbiome diversity and function of Kellet's whelk (Kelletia kelletii) perivitelline fluid (PVF), which sustains thousands of developing K. kelletii embryos within a polysaccharide and protein matrix. Our core microbiome analysis reveals a diverse range of bacteria, with the Roseobacter genus being the most abundant. Additionally, genes related to host-microbe interactions, symbiosis, and quorum sensing were detected, indicating a potential symbiotic relationship between the microbiome and Kellet's whelk embryos. Furthermore, the microbiome exhibits gene expression related to antibiotic biosynthesis, suggesting a defensive role against pathogenic bacteria and potential discovery of novel antibiotics. Overall, this study sheds light on the microbiome's role in Kellet's whelk development, emphasizing the significance of host-microbe interactions in vulnerable life history stages. To our knowledge, ours is the first study to use 16S sequencing coupled with RNA sequencing (RNA-seq) to profile the microbiome of an invertebrate PVF.IMPORTANCEThis study provides novel insight to an encapsulated system with strong evidence of symbiosis between the microbial inhabitants and developing host embryos. The Kellet's whelk perivitelline fluid (PVF) contains microbial organisms of interest that may be providing symbiotic functions and potential antimicrobial properties during this vulnerable life history stage. This study, the first to utilize a comprehensive approach to investigating Kellet's whelk PVF microbiome, couples 16S rRNA gene long-read sequencing with RNA-seq. This research contributes to and expands our knowledge on the roles of beneficial host-associated microbes.

Gut microbiota dynamics interacting with gastrointestinal evacuation of Apostichopus japonicus: novel insights into promising strategies for environmental improvement

As an important input of environmental micropollutants into aquaculture environment, feed is now considered to be a critical factor in shaping gastrointestinal evacuation characteristics of animals. We analyzed the gastrointestinal evacuation characteristics and gut bacteria of Apostichopus japonicus within 30 h after feeding in recirculating aquaculture system (RAS) and explored the evacuation mechanism interacting by bacteria. The Gauss model was the most precise gastrointestinal evacuation curve, and 80% of gastrointestinal evacuation time was 27.81 h after feeding. Linear discriminant analysis effect size analysis revealed that gut microbial abundance associated significantly with time (P < 0.05), and 42 biomarkers that could predict gastrointestinal evacuation were totally detected, such as Lutibacter and Vibrio. Biomarkers at 25 h after feeding were related to harmful bacteria. A dynamic response between gastrointestinal content ratio and gut microbial abundance was detected. Taken together, we could discharge sewage about 25 h after feeding and carry out the next round of feeding activities.

Physiological Response of Spotted Seabass (Lateolabrax maculatus) to Different Dietary Available Phosphorus Levels and Water Temperature: Changes in Growth, Lipid Metabolism, Antioxidant Status and Intestinal Microbiota

A 10-week growth experiment was conducted to assess the physiological response of spotted seabass (Lateolabrax maculatus) raised at moderate (27 °C) and high temperatures (33 °C) to different dietary available phosphorus (P) levels. Five diets with available P levels of 0.35, 0.55, 0.71, 0.82 and 0.92% were formulated, respectively. A water temperature of 33 °C significantly decreased growth performance and feed utilization, and increased oxidative stress and lipid deposition of spotted seabass compared with 27 °C. A second-order polynomial regression analysis based on weight gain (WG) showed that the available P requirement of spotted seabass raised at 27 °C and 33 °C was 0.72% and 0.78%, respectively. The addition of 0.71-0.82% P to the diet improved the growth performance, feed utilization, and antioxidant capacity of spotted seabass and alleviated the excessive lipid deposition compared with the low-P diet (0.35% P). Moreover, the addition of 0.71-0.92% P to diets increased the diversity of intestinal microbiota and the relative abundance of Lactococcus lactis and decreased the relative abundance of Plesiomonas compared with the low-P diet. Thus, dietary supplementation with 0.71-0.82% P improved the growth performance, antioxidant capacity and microbial composition of spotted seabass, and alleviated the disturbance of lipid metabolism caused by high temperature or low-P diet.

Gut microbiota in parasite-transmitting gastropods

BACKGROUND

Gastropoda, the largest class within the phylum Mollusca, houses diverse gut microbiota, and some gastropods serve as intermediate hosts for parasites. Studies have revealed that gut bacteria in gastropods are associated with various biological aspects, such as growth, immunity and host-parasite interactions. Here, we summarize our current knowledge of gastropod gut microbiomes and highlight future research priorities and perspectives.

METHODS

A literature search was undertaken using PubMed, Web of Science and CNKI for the articles on the gut microbiota of gastropods until December 31, 2022. We retrieved a total of 166 articles and identified 73 eligible articles for inclusion in this review based on the inclusion and exclusion criteria.

RESULTS

Our analysis encompassed freshwater, seawater and land snails, with a specific focus on parasite-transmitting gastropods. We found that most studies on gastropod gut microbiota have primarily utilized 16S rRNA gene sequencing to analyze microbial composition, rather than employing metagenomic, metatranscriptomic, or metabolomic approaches. This comprehensive review provided an overview of the parasites carried by snail species in the context of gut microbiota studies. We presented the gut microbial trends, a comprehensive summary of the diversity and composition, influencing factors, and potential functions of gastropod gut microbiota. Additionally, we discussed the potential applications, research gaps and future perspectives of gut microbiomes in parasite-transmitting gastropods. Furthermore, several strategies for enhancing our comprehension of gut microbiomes in snails were also discussed.

CONCLUSIONS

This review comprehensively summarizes the current knowledge on the composition, potential function, influencing factors, potential applications, limitations, and challenges of gut microbiomes in gastropods, with a specific emphasis on parasite-transmitting gastropods. These findings provide important insights for future studies aiming to understand the potential role of gastropod gut microbiota in controlling snail populations and snail-borne diseases.

Physiological stress responses of European sea bass Dicentrarchus labrax related to changing operations of floating net cages in intensive farming conditions at the Moroccan M'diq Bay

The present study aimed to quantify and compare in situ the primary and secondary physiological stress responses, related to the changing operations of floating net cages, in both subadult (523 days post hatching [dph]) and adult (916 dph) European sea bass Dicentrarchus labrax under intensive farming conditions in the Moroccan M'diq Bay. The blood levels of cortisol, glucose, total cholesterol, total protein, and lactate, as well as the percentage of haematocrit, were measured before and after this operation. The results showed significantly elevated levels of cortisol and blood glucose in both age groups, whereas total cholesterol and protein levels were unaffected. In fact, blood lactate significantly decreased in subadults, whereas in adults this parameter was not affected by the operation. However, the haematocrit percentages measured after the operation were significantly higher than those found before the operation in both groups of fish, which is attributed to the increased rate of oxygen renewal in the new net cages and the lower water temperature inside the cages. With regard to the age-specific response during this essential operation plasma cortisol, blood glucose, and lactate concentrations, as well as plasma total protein levels, were significantly higher in subadults than in adults, in both pre- and post- stress measurement, with the presence of individual-specific response. It is concluded that aquaculture practices such as changing the aquaculture net cage could have repercussions in terms of the classic physiological responses to stress in D. labrax.

Persistent Dysbiosis, Parasite Rise and Growth Impairment in Aquacultured European Seabass after Oxytetracycline Treatment

The use of antibiotics in open-water aquaculture is often unavoidable when faced with pathogens with high mortality rates. In addition, seasonal pathogen surges have become more common and more intense over the years. Apart from the apparent cost of antibiotic treatment, it has been observed that, in aquaculture practice, the surviving fish often display measurable growth impairment. To understand the role of gut microbiota on the observed growth impairment, in this study, we follow the incidence of Photobacterium damselae subsp. piscicida in a seabass commercial open-water aquaculture setting in Galaxidi (Greece). Fish around 10 months of age were fed with feed containing oxytetracycline (120 mg/kg/day) for twelve days, followed by a twelve-day withdrawal period, and another eighteen days of treatment. The fish were sampled 19 days before the start of the first treatment and one month after the end of the second treatment cycle. Sequencing of the 16S rRNA gene was used to measure changes in the gut microbiome. Overall, the gut microbiota community, even a month after treatment, was highly dysbiotic and characterized by very low alpha diversity. High abundances of alkalophilic bacteria in the post-antibiotic-treated fish indicated a rise in pH that was coupled with a significant increase in gut parasites. This study's results indicate that oxytetracycline (OTC) treatment causes persistent dysbiosis even one month after withdrawal and provides a more suitable environment for an increase in parasites. These findings highlight the need for interventions to restore a healthy and protective gut microbiome.

An in-depth characterisation of European seabass intestinal segments for assessing the impact of an algae-based functional diet on intestinal health

Sustainable farming of fish species depends on emerging new feed ingredients, which can alter the features of the digestive tract and influence animals' overall health. Recent research has shown that functional feeds hold great potential for enhancing fish robustness by evoking appropriate responses at the intestine level. However, there is a lack of extensive and accurate descriptions of the morphology of the gastrointestinal tract of most farmed fish. We have characterised the intestine of European seabass thoroughly, by targeting four segments - anterior, mid, posterior and rectum. Results indicated that the anterior segment is mostly associated with absorption-related features; this segment has the largest absorptive area, the longest villi, and the highest number of neutral goblet cells (GC). The posterior segment and rectum have distinct histomorphometric features, but both seem to be important for immunity, displaying the highest count of acid GC and the highest expression of immune-related genes. The strongest proliferating cell nuclear antigen (PCNA) signal was observed in the anterior intestine and rectum, with PCNA⁺ cells appearing at the base of the villi and the corresponding villi branches. We have also evaluated the impact of a novel feed supplemented with a macro- and microalgae blend and found that there were no differences in terms of growth. However, the alterations observed in the mid intestine of fish fed the blend, such as thickening of the submucosa and lamina propria, an increased number of leucocytes, and higher expression of immune- and oxidative stress-related genes, suggest that algae may have an immunomodulatory effect. In the current article, we have described the morphology and expression patterns of the intestine segments of European seabass in detail and have presented a comprehensive report of the indices and methods used for the semi-quantitative and quantitative histomorphometric assessments, thereby providing useful information for future studies that aim to maintain intestinal health through dietary interventions.

Factors Determining the Susceptibility of Fish to Effects of Human Pharmaceuticals

The increasing levels and frequencies at which active pharmaceutical ingredients (APIs) are being detected in the environment are of significant concern, especially considering the potential adverse effects they may have on nontarget species such as fish. With many pharmaceuticals lacking environmental risk assessments, there is a need to better define and understand the potential risks that APIs and their biotransformation products pose to fish, while still minimizing the use of experimental animals. There are both extrinsic (environment- and drug-related) and intrinsic (fish-related) factors that make fish potentially vulnerable to the effects of human drugs, but which are not necessarily captured in nonfish tests. This critical review explores these factors, particularly focusing on the distinctive physiological processes in fish that underlie drug absorption, distribution, metabolism, excretion and toxicity (ADMET). Focal points include the impact of fish life stage and species on drug absorption (A) via multiple routes; the potential implications of fish's unique blood pH and plasma composition on the distribution (D) of drug molecules throughout the body; how fish's endothermic nature and the varied expression and activity of drug-metabolizing enzymes in their tissues may affect drug metabolism (M); and how their distinctive physiologies may impact the relative contribution of different excretory organs to the excretion (E) of APIs and metabolites. These discussions give insight into where existing data on drug properties, pharmacokinetics and pharmacodynamics from mammalian and clinical studies may or may not help to inform on environmental risks of APIs in fish.

Mediterranean Sea heatwaves jeopardize greater amberjack's (Seriola dumerili) aquaculture productivity through impacts on the fish microbiota

Climate change is dramatically increasing the frequency and severity of marine heatwaves (MHWs) in the Mediterranean basin, strongly affecting marine food production systems. However, how it will shape the ecology of aquaculture systems, and the cascading effects on productivity, is still a major knowledge gap. The present work aims to increase our understanding of future impacts, caused by raising water temperatures, on the interaction between water and fish microbiotas, and consequential effects upon fish growth. Thus, the bacterial communities present in the water tanks, and mucosal tissues (skin, gills and gut), of greater amberjack farmed in recirculatory aquaculture systems (RAS), at three different temperatures (24, 29 and 33 °C), were characterized in a longitudinal study. The greater amberjack (Seriola dumerili) is a teleost species with high potential for EU aquaculture diversification due to its fast growth, excellent flesh quality and global market. We show that higher water temperatures disrupt the greater amberjack's microbiota. Our results demonstrate the causal mediation exerted by this bacterial community shifts on the reduction of fish growth. The abundance of members of the Pseudoalteromonas is positively correlated with fish performance, whereas members of the Psychrobacter, Chryseomicrobium, Paracoccus and Enterovibrio are suggested as biomarkers for dysbiosis, at higher water temperatures. Hence, opening new evidence-based avenues for the development of targeted microbiota-based biotechnological tools, designed to increase the resilience and adaptation to climate change of the Mediterranean aquaculture industry.

Gut microbiota of two invasive fishes respond differently to temperature

Temperature variation structures the composition and diversity of gut microbiomes in ectothermic animals, key regulators of host physiology, with potential benefit to host or lead to converse results (i.e., negative). So, the significance of either effect may largely depend on the length of time exposed to extreme temperatures and how rapidly the gut microbiota can be altered by change in temperature. However, the temporal effects of temperature on gut microbiota have rarely been clarified. To understand this issue, we exposed two juvenile fishes (Cyprinus carpio and Micropterus salmoides), which both ranked among the 100 worst invasive alien species in the world, to increased environmental temperature and sampled of the gut microbiota at multiple time points after exposure so as to determine when differences in these communities become detectable. Further, how temperature affects the composition and function of microbiota was examined by comparing predicted metagenomic profiles of gut microbiota between treatment groups at the final time point of the experiment. The gut microbiota of C. carpio was more plastic than those of M. salmoides. Specifically, communities of C. carpio were greatly altered by increased temperature within 1 week, while communities of M. salmoides exhibit no significant changes. Further, we identified 10 predicted bacterial functional pathways in C. carpio that were temperature-dependent, while none functional pathways in M. salmoides was found to be temperature-dependent. Thus, the gut microbiota of C. carpio was more sensitive to temperature changes and their functional pathways were significantly changed after temperature treatment. These results showed the gut microbiota of the two invasive fishes differ in response to temperature change, which may indicate that they differ in colonization modes. Broadly, we have confirmed that the increased short-term fluctuations in temperatures are always expected to alter the gut microbiota of ectothermic vertebrates when facing global climate change.

Gut microbiome composition associates with corticosteroid treatment, morbidity, and senescence in Chinook salmon (Oncorhynchus tshawytscha)

Pacific salmon experience prolonged elevation in corticosteroid hormones during important life history events including migration, reproduction, and senescence. These periods of elevated corticosteroids correspond with changes to immunity and energy metabolism; therefore, fish may be particularly vulnerable to mortality at these times. Recent studies found that stress-induced cortisol release associated with microbial community shifts in salmonids, raising the question of how longer-term corticosteroid dynamics that accompany life history transitions affect salmonid microbiomes. In this work, we experimentally evaluated the relationships between gut microbiome composition, chronically elevated corticosteroids, and mortality in juvenile Chinook salmon (Oncorhynchus tshawytscha). We found that treatment with slow-release implants of the corticosteroids cortisol or dexamethasone resulted in changes to the gut microbiome. Morbidity was also associated with microbiome composition, suggesting that the gut microbiome reflects individual differences in susceptibility to opportunistic pathogens. Additionally, we analyzed a small number of samples from adult fish at various stages of senescence. Results from these samples suggest that microbiome composition associated with gut integrity, and that the microbial communities of corticosteroid treated juveniles shift in composition toward those of senescent adults. Overall, findings from this work indicate that the gut microbiome correlates with mortality risk during periods of chronic corticosteroid elevation.

Transcriptome analysis reveals the high temperature induced damage is a significant factor affecting the osmotic function of gill tissue in Siberian sturgeon (Acipenser baerii)

BACKGROUND

Maintaining osmotic equilibrium plays an important role in the survival of cold-water fishes. Heat stress has been proven to reduce the activity of Na⁺/K⁺-ATPase in the gill tissue, leading to destruction of the osmotic equilibrium. However, the mechanism of megatemperature affecting gill osmoregulation has not been fully elucidated.

RESULTS

In this study, Siberian sturgeon (Acipenser baerii) was used to analyze histopathological change, plasma ion level, and transcriptome of gill tissue subjected to 20℃, 24℃and 28℃. The results showed that ROS level and damage were increased in gill tissue with the increasing of heat stress temperature. Plasma Cl^- level at 28℃ was distinctly lower than that at 20℃ and 24℃, while no significant difference was found in Na⁺ and K⁺ ion levels among different groups. Transcriptome analysis displayed that osmoregulation-, DNA-repair- and apoptosis-related terms or pathways were enriched in GO and KEGG analysis. Moreover, 194 osmoregulation-related genes were identified. Amongst, the expression of genes limiting ion outflow, occluding (OCLN), and ion absorption, solute carrier family 4, member 2 (AE2) solute carrier family 9, member 3 (NHE3) chloride channel 2 (CLC-2) were increased, while Na⁺/K⁺-ATPase alpha (NKA-a) expression was decreased after heat stress.

CONCLUSIONS

This study reveals for the first time that the effect of heat stress on damage and osmotic regulation in gill tissue of cold-water fishes. Heat stress increases the permeability of fish's gill tissue, and induces the gill tissue to keep ion balance through active ion absorption and passive ion outflow. Our study will contribute to research of global-warming-caused effects on cold-water fishes.

Exploring the interactions between the gut microbiome and the shifting surrounding aquatic environment in fisheries and aquaculture: A review

The rise of "new" sequencing technologies and the development of sophisticated bioinformatics tools have dramatically increased the study of the aquaculture microbiome. Microbial communities exist in complex and dynamic communities that play a vital role in the stability of healthy ecosystems. The gut microbiome contributes to multiple aspects of the host's physiological health status, ranging from nutritional regulation to immune modulation. Although studies of the gut microbiome in aquaculture are growing rapidly, the interrelationships between the aquaculture microbiome and its aquatic environment have not been discussed and summarized. In particular, few reviews have focused on the potential mechanisms driving the alteration of the gut microbiome by surrounding aquatic environmental factors. Here, we review current knowledge on the host gut microbiome and its interrelationship with the microbiome of the surrounding environment, mainly including the main methods for characterizing the gut microbiome, the composition and function of microbial communities, the dynamics of microbial interactions, and the relationship between the gut microbiome and the surrounding water/sediment microbiome. Our review highlights two potential mechanisms for how surrounding aquatic environmental factors drive the gut microbiome. This may deepen the understanding of the interactions between the microbiome and environmental factors. Lastly, we also briefly describe the research gaps in current knowledge and prospects for the future orientation of research. This review provides a framework for studying the complex relationship between the host gut microbiome and environmental stresses to better facilitate the widespread application of microbiome technologies in fisheries and aquaculture.

Characterization of Gut Microbiome in the Mud Snail Cipangopaludina cathayensis in Response to High-Temperature Stress

Simple Summary

This study investigated the effects of high-temperature stress on the intestinal microbiome of Cipangopaludina cathayensis. High-temperature exposure significantly changed the intestinal microbiota structure of C. cathayensis. The relative abundance of putatively beneficial bacteria decreased, whereas the relative abundance of putatively pathogenic bacteria increased after thermal stress. Consistent with the trends of change in the intestinal microbiota, the high-temperature treatment inhibited some carbohydrate metabolism pathways and induced certain disease-related pathways. Thermal stress disrupts the homeostasis of gut microbiota, which may lead to disease outbreak in C. cathayensis.

Abstract

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

Effects of cadmium exposure on intestinal microflora of Cipangopaludina cathayensis

As one of the most environmentally toxic heavy metals, cadmium (Cd) has attracted the attention of researchers globally. In particular, Guangxi, a province in southwestern China, has been subjected to severe Cd pollution due to geogenic processes and anthropogenic activities. Cd can be accumulated in aquatic animals and transferred to the human body through the food chain, with potential health risks. The aim of the present study was to explore the effects of waterborne Cd exposure (0.5 mg/L and 1.5 mg/L) on the intestinal microbiota of mudsnail, Cipangopaludina cathayensis, which is favored by farmers and consumers in Guangxi. Gut bacterial community composition was investigated using high-throughput sequencing of the V3–V4 segment of the bacterial 16S rRNA gene. Our results indicated that C. cathayensis could tolerate low Cd (0.5 mg/L) stress, while Cd exposure at high doses (1.5 mg/L) exerted considerable effects on microbiota composition. At the phylum level, Proteobacteria, Bacteroidetes, and Firmicutes were the dominant phyla in the mudsnail gut microbiota. The relative abundances of Bacteroidetes increased significantly under high Cd exposure (H14) (p < 0.01), with no significant change in the low Cd exposure (L14) treatment. The dominant genera with significant differences in relative abundance were Pseudomonas, Cloacibacterium, Acinetobacter, Dechloromonas, and Rhodobacter. In addition, Cd exposure could significantly alter the pathways associated with metabolism, cellular processes, environmental information processing, genetic information processing, human diseases, and organismal systems. Notably, compared to the L14 treatment, some disease-related pathways were enriched, while some xenobiotic and organic compound biodegradation and metabolism pathways were significantly inhibited in the H14 group. Overall, Cd exposure profoundly influenced community structure and function of gut microbiota, which may in turn influence C. cathayensis gut homeostasis and health.

Seasonal variation in structure and function of gut microbiota in Pomacea canaliculata

Gut microbiota is associated with host health and its environmental adaption, influenced by seasonal variation. Pomacea canaliculata is one of the world's 100 worst invasive alien species. Here, we used high-throughput sequencing of the 16S rRNA gene to analyze the seasonal variation of gut microbiota of P. canaliculata. The results suggested that the predominant gut microbial phyla of P. canaliculata included Firmicutes and Proteobacteria, which helped digest plant food and accumulate energy. The gut microbiota of P. canaliculata in summer group showed the highest diversity, whereas the winter group possessed the lowest, probably due to the shortage of food resources of P. canaliculata in winter. Principal coordinate analysis analysis based on unweighted unifrac and weighted unifrac indicated that the composition of gut microbiota of P. canaliculata significantly varied across seasons. Bacteroidetes tended to be enriched in summer by linear discriminant analysis effect size analysis. Actinobacteria and Cyanobacteria were extremely abundant in autumn, while Fusobacteria and Cetobacterium enriched in winter. In conclusion, the structure of the gut microbiota of P. canaliculata was significantly different among seasons, which was beneficial to the environment adaptation and the digestion and metabolism of food during different periods.