Sodium salt medium-chain fatty acids and Bacillus-based probiotic strategies to improve growth and intestinal health of gilthead sea bream (Sparus aurata)

The Expansion of Sirtuin Gene Family in Gilthead Sea Bream (Sparus aurata)-Phylogenetic, Syntenic, and Functional Insights across the Vertebrate/Fish Lineage

The Sirtuin (SIRT1-7) family comprises seven evolutionary-conserved enzymes that couple cellular NAD availability with health, nutrition and welfare status in vertebrates. This study re-annotated the sirt3/5 branch in the gilthead sea bream, revealing three paralogues of sirt3 (sirt3.1a/sirt3.1b/sirt3.2) and two of sirt5 (sirt5a/sirt5b) in this Perciform fish. The phylogeny and synteny analyses unveiled that the Sirt3.1/Sirt3.2 dichotomy was retained in teleosts and aquatic-living Sarcopterygian after early vertebrate 2R whole genome duplication (WGD). Additionally, only certain percomorphaceae and gilthead sea bream showed a conserved tandem-duplicated synteny block involving the mammalian-clustered sirt3.1 gene (psmd13-sirt3.1a/b-drd4-cdhr5-ctsd). Conversely, the expansion of the Sirt5 branch was shaped by the teleost-specific 3R WGD. As extensively reviewed in the literature, human-orthologues (sirt3.1/sirt5a) showed a high, conserved expression in skeletal muscle that increased as development advanced. However, recent sirt3.2 and sirt5b suffered an overall muscle transcriptional silencing across life, as well as an enhanced expression on immune-relevant tissues and gills. These findings fill gaps in the ontogeny and differentiation of Sirt genes in the environmentally adaptable gilthead sea bream, becoming a good starting point to advance towards a full understanding of its neo-functionalization. The mechanisms originating from these new paralogs also open new perspectives in the study of cellular energy sensing processes in vertebrates.

Nutritional impact of nano zeolite, probiotic, and fatty acids as feed additives on health status of Nile tilapia (Oreochromis niloticus)

For human consumption, fish is a good and affordable source of several crucial elements. Growing aquaculture management and output is always necessary. Therefore, this study was designed to evaluate the effect of probiotics, nano zeolite, and/or medium chain fatty acids (MCFA) on fish health and the chemical composition of the fish body. The experimental fish were distributed into eight groups. T1: Control group fed the basal diet without feed additives, T2: Nano zeolite at a rate of 2 mg/kg diet, T3: Pedococcus at a rate of 2 gm kg diet, T4: Medium chain fatty acids used according to produced company recommendation at a rate of 3.5 gm/kg diet, T5: Nano zeolite (2 mg/kg diet) + Pedococcus (2 mg/kg diet), T6: Nano zeolite (2 mg/kg diet) + Medium chain fatty acids (3.5 gm/kg diet), T7: Pedococcus (2 mg/kg diet) + Medium chain fatty acids (3.5 gm/kg diet), and T8: Nano zeolite (2 mg/kg diet) + Pedococcus (2 mg/kg diet) + Medium chain fatty acids (3.5 gm/kg diet). The obtained results showed an insignificant difference in the body composition of Nile tilapia fish fed feed additives alone or in combination. Moreover, the feed additives did not affect the health status of fish, as indicated by normal liver and kidney functions.

Current Development and Future Application Prospects of Plants-Derived Polyphenol Bioactive Substance Curcumin as a Novel Feed Additive in Livestock and Poultry

Curcumin (CUR) is a kind of natural orange-yellow phenolic compound mainly extracted from the stems and roots of turmeric plants and other species in the genus Curcuma, furthermore, it is also the most important active ingredient exerting pharmacological functions in turmeric. In recent years, CUR has been frequently reported and has attracted widespread attention from scholars all over the world due to its numerous biological functions and good application prospects, such as anti-inflammatory, anticancer, antioxidant and providing lipid-lowering effects, etc. In addition, adding a certain dose of CUR to livestock and poultry feed is important for animal growth and development, which plays a key role in animal metabolism, reproduction, immunity and clinical health care. This review aims to summarize, based on the published papers and our own observations, the physical and chemical properties and the biological functions of the plant-derived bioactive ingredient CUR, especially regarding the latest research progress in regulating intestinal health as well as its current development and future application prospects in livestock and poultry as a novel feed additive, so as to provide theoretical and practical references for the further study of the application of CUR as a novel feed additive and a potential new antibiotic substitute, thereby improving the research field of plant-derived bioactive ingredients and promoting the healthy development of livestock and poultry.

Effects of the Replacement of Dietary Fish Meal with Defatted Yellow Mealworm (Tenebrio molitor) on Juvenile Large Yellow Croakers (Larimichthys crocea) Growth and Gut Health

Simple Summary

Fish meal is the most common protein source in aquatic feeds. The decline of fishery resources and the increased demand have led to a shortage of fish meal resources in recent years. To ensure the sustainable development of the aquaculture industry, it is crucial to find a low-price, high-quality protein source to replace fish meal. In this study, substituting fish meal of large yellow croakers (Larimichthys crocea) diets with defatted yellow mealworm (Tenebrio molitor) test was carried out. The results showed that the dietary fish meal could be replaced by 15% defatted yellow mealworm in feeds containing 40% fish meal without adversely affecting the growth of large yellow croakers, and to some extent improving the immunity of the organism. Substitution levels of 15% or more are beneficial for digestive enzymes. In addition, the moderate addition of defatted yellow mealworm improves intestinal health by improving the structure and microbial composition of the gut.

Abstract

This study was conducted to investigate the effects of Tenebrio molitor meal (TM) replacement for fish meal (FM) on growth performance, humoral immunity, and intestinal health of juvenile large yellow croakers (Larimichthys crocea). Four experimental diets were formulated by replacing FM with TM at different levels—0% (TM0), 15% (TM15), 30% (TM30), and 45% (TM45). Triplicate groups of juveniles (initial weight = 11.80 ± 0.02 g) were fed the test diets to apparent satiation two times daily for eight weeks. There was no significant difference in final body weight (FBW) and weight gain rate (WG) among TM0, TM15, and TM30, while TM45 feeding significantly reduced the FBW and WG. Compared with TM0, AKP activity in serum was significantly decreased in TM45, while the TM15 group remarkably increased LZM activity. TM30 showed significantly higher serum C3 levels compared to the TM0 group, while the TM addition groups decreased the C4 levels significantly in the serum. In terms of intestinal histology, the addition of TM increased the height and thickness of the intestinal villus and also increased the thickness of the intestinal muscles significantly. The addition of TM significantly reduced the serum DAO and D-lactate concentrations. The results of 16S rRNA gene sequencing showed that the addition of TM significantly enhanced the relative abundance of Bacilli and Lactobacillus and contributed to the decrease in the relative abundance of Plesiomonas. In addition, the TM30 and TM45 groups significantly reduced the abundance of Peptostreptococcaceae. Overall, our results indicated that TM could be a viable alternative protein source, 6.7% TM supplantation (replacing 15% FM) in large yellow croaker feed improved humoral immunity and intestinal health with no adverse effects on growth. Furthermore, the replacement of FM with 30% and 45% TM adversely affects growth and humoral immunity.

Possible role of transcription factors (BSX, NKX2.1, IRX3 and SIRT1) in the regulation of appetite in goldfish (Carassius auratus)

The homeobox genes play important roles in the embryonic development of animals. Recent evidence suggests they might also regulate feeding and act as transcription factors of appetite regulators. Examples of these genes are a brain-specific homeobox transcription factor (BSX), NK2 homeobox 1 (NKX2.1) and the Iroquois homeobox 3 (IRX3). Sirtuin1 (SIRT1) acts as a transcription factor for nutrient (e.g. lipid, glucose) homeostasis and responds to stress and nutrient availability, and has been shown to interact with appetite regulators. Very little is known about the role of these genes in the regulation of feeding and nutrient homeostasis in fish. In this study, we assessed the roles of BSX, NKX2.1, IRX3 and SIRT1 in the central regulation of feeding in goldfish by examining their mRNA brain distribution, assessing the effects of fasting on their brain expression and assessing the effects of peripheral injections of cholecystokinin (CCK, a brain-gut peptide), on their brain expression. All genes showed a widespread distribution in the brain, with high levels in the hypothalamus. In both hypothalamus and telencephalon, fasting induced increases in BSX, IRX3 and NKX2.1 expressions but had no effect on SIRT1 expression levels. CCK injections increased hypothalamic expression levels of IRX3 and SIRT1, and telencephalic expression levels of NKX2.1 and SIRT1, with no effect on either hypothalamic BSX or NKX2.1 expression levels or telencephalon BSX or IRX3 expression levels. Our results suggest that, in goldfish as in mammals, central BSX, NKX2.1, IRX3 and SIRT1 are present in regions of the brain regulating feeding, are sensitive to nutrient status and interact with appetite-regulating peptides.

Effect of dietary supplementation of lauric acid on growth performance, antioxidative capacity, intestinal development and gut microbiota on black sea bream (Acanthopagrus schlegelii)

A feeding trial of eight weeks was conducted to examine the influence of food supplementation with lauric acid (LA) on Acanthopagrus schlegelii (juvenile black sea bream). A 24 percent fish meal baseline diet was created, while the other two diets were generated with dietary supplementation of graded points of LA at 0.1 percent and 0.8 percent, respectively. Each diet was given a triplicate tank with 20 fish weighing 6.22 ± 0.19 g. In comparison with the control group, the weight gain rate, growth rate, as well as feed efficiency of fish fed of 0.1 percent diet of LA were considerably (P < 0.05) greater. The total body and dorsal muscle proximate compositions did not change significantly between groups (P > 0.05). Triglyceride (TG) content was considerably (P < 0.05) greater in the LA-supplemented meals eating group in comparison with the control group. In the group eating LA-supplemented meals, the height of villus and the number of goblet cells/villus were considerably (P < 0.05) larger. The microbial makeup of the gut was also studied. The differences in phyla, class, and family level were not statistically significant (P > 0.05). Firmicutes in the phylum, Betaproteobacteri, Gammaproteobacteria, and Clostridia in the class, and Clostridiaceae in the family were all substantially increased with higher levels of LA supplementation (P < 0.05). According to the findings of this study, an LA-supplemented diet improves fish development, antioxidative capability, gut microbiota and intestinal health.

Autochthonous Probiotics Alleviate the Adverse Effects of Dietary Histamine in Juvenile Grouper (Epinephelus coioides)

High dose (0.3%) of dietary histamine can cause adverse effects on growth performance, innate immunity, and gut health in juvenile grouper (Epinephelus coioides). In the present study, three autochthonous probiotics (Bacillus pumilus SE5, Psychrobacter sp. SE6, and Bacillus clausii DE5) were supplemented separately to diets containing 0.3% of histamine and their effects on growth performance, innate immunity, and gut health of grouper (E. coioides) were evaluated in a 56-day feeding trial. The results showed considerable increase in weight gain, specific growth rate, hepatosomatic index, and decreased feed conversion rate in groupers fed with probiotic-supplemented diets. Supplementation of autochthonous probiotics has improved antioxidant capacity and innate immunity of E. coioides by measuring correlative parameters, such as total antioxidant capacity, superoxide dismutase activity, malondialdehyde content, and so on. Additionally, dietary probiotics have significantly reduced the levels of serum interleukin-1β (at days 28 and 56), fatty acid-binding protein 2, and intestinal trefoil factor (at day 28), and promoted intestinal integrity following remarkably increased muscle thickness and mucosal fold height at day 56, especially in grouper fed with B. pumilus SE5 containing diet (P < 0.05). On day 56, the gut microbial composition of E. coioides was positively shaped by autochthonous probiotics, the relative abundance of potentially pathogenic Photobacterium decreased while beneficial Lactobacillus increased in fish fed with probiotic strains, especially with B. pumilus SE5 and B. clausii DE5. These results suggest that among the three autochthonous probiotic strains tested, B. pumilus SE5 is showing better efficiency in alleviating the adverse effects of (high levels) dietary histamine by decreasing the expression of inflammatory markers and by improving the growth, innate immunity, and gut health of juvenile grouper E. coioides.

Cross-Talk Between Intestinal Microbiota and Host Gene Expression in Gilthead Sea Bream (Sparus aurata) Juveniles: Insights in Fish Feeds for Increased Circularity and Resource Utilization

New types of fish feed based on processed animal proteins (PAPs), insect meal, yeast, and microbial biomasses have been used with success in gilthead sea bream. However, some drawback effects on feed conversion and inflammatory systemic markers were reported in different degrees with PAP- and non-PAP-based feed formulations. Here, we focused on the effects of control and two experimental diets on gut mucosal-adherent microbiota, and how it correlated with host transcriptomics at the local (intestine) and systemic (liver and head kidney) levels. The use of tissue-specific PCR-arrays of 93 genes in total rendered 13, 12, and 9 differentially expressed (DE) genes in the intestine, liver, and head kidney, respectively. Illumina sequencing of gut microbiota yielded a mean of 125,350 reads per sample, assigned to 1,281 operational taxonomic unit (OTUs). Bacterial richness and alpha diversity were lower in fish fed with the PAP diet, and discriminant analysis displayed 135 OTUs driving the separation between groups with 43 taxa correlating with 27 DE genes. The highest expression of intestinal pcna and alpi was achieved in PAP fish with intermediate values in non-PAP, being the pro-inflammatory action of alpi associated with the presence of Psychrobacter piscatorii. The intestinal muc13 gene was down-regulated in non-PAP fish, with this gene being negatively correlated with anaerobic (Chloroflexi and Anoxybacillus) and metal-reducing (Pelosinus and Psychrosinus) bacteria. Other inflammatory markers (igm, il8, tnfα) were up-regulated in PAP fish, positively correlating the intestinal igm gene with the inflammasome activator Escherichia/Shigella, whereas the systemic expression of il8 and tnfα was negatively correlated with the Bacilli class in PAP fish and positively correlated with Paracoccus yeei in non-PAP fish. Overall changes in the expression pattern of il10, galectins (lgals1, lgals8), and toll-like receptors (tlr2, tlr5, tlr9) reinforced the anti-inflammatory profile of fish fed with the non-PAP diet, with these gene markers being associated with a wide range of OTUs. A gut microbiota-liver axis was also established, linking the microbial generation of short chain fatty acids with the fueling of scd1- and elovl6-mediated lipogenesis. In summary, by correlating the microbiome with host gene expression, we offer new insights in the evaluation of fish diets promoting gut and metabolism homeostasis, and ultimately, the health of farmed fish.

Serum metabolome and gut microbiome alterations in broiler chickens supplemented with lauric acid

Antibiotic overuse in poultry husbandry poses a potential threat to meat safety and human health. Lauric acid (LA) is a primary medium-chain fatty acid (MCFA) with a strong antibacterial capacity. The goal of this study was to evaluate the beneficial effects of LA on the growth performance, immune responses, serum metabolism, and cecal microbiota of broiler chickens. One-day-old male Ross 308 broilers were randomly divided into 4 groups: CON, fed a basal diet; ANT, a basal diet supplemented with 75 mg/kg antibiotic; LA500, a basal diet supplemented with 500 mg/kg LA; LA1000, a basal diet supplemented with 1000 mg/kg LA. The feeding period was 42 d. The results showed that LA significantly improved broiler growth and immune functions, as evidenced by increased body weight (BW) and average daily gain (ADG), enhanced intestinal mucosal barrier, upregulated immunoglobulins (IgA, IgM, and IgY), and downregulated inflammatory cytokines (IL-1β, IL-6, TNF-α, IL-4, and IL-10) (P < 0.05). HPLC/MS-based metabolome analysis revealed that the serum metabolites in the LA group differed from those of CON and ANT groups. LA markedly decreased the abundance of phosphatidylcholines (PCs), increased lysophosphatidylcholines (LysoPCs), and inhibited the sphingolipid metabolism pathway, indicating its capacity to modulate lipid metabolism. 16S rRNA sequencing indicated that LA significantly altered cecal microbiota composition by reducing Phascolarctobacterium, Christensenellaceae_R-7_group, and Bacteroides, and increasing Faecalibacterium and Ruminococcaceae_UCG-014 (P < 0.05). Furthermore, Spearman correlation analysis revealed that changes in metabolism and microbiota were highly correlated with the growth and immune indices; strong links were also found between lipid metabolism and microbial composition. Taken together, LA promotes broiler growth and immune functions by regulating lipid metabolism and gut microbiota. The above findings highlight the substantial potential of LA as a supplement in poultry diets and provide a new strategy to reduce antibiotic usage and improve food safety.

Low dietary inclusion of nutraceuticals from microalgae improves feed efficiency and modifies intermediary metabolisms in gilthead sea bream (Sparus aurata)

The aim of this work was to evaluate two functional feeds for the gilthead seabream, Sparus aurata, containing low inclusion of two microalgae-based products (LB-GREENboost, LB_Gb; and LB-GUThealth, LB_Gh). Fish (12–13 g) were fed for 13 weeks a control diet or one of the four diets supplemented with both products at 0.5% or 1%. LB_Gb and LB_Gh did not affect specific growth rate or survival, but increased feed efficiency by decreasing feed intake and enlarging the intestines. LB_Gb increased hepatosomatic index and reduced cortisol levels in plasma, while both products lowered plasma lactate. Extensive metabolite and metabolic enzyme profiling revealed that microalgae supplementations, especially 1% LB_Gh: (i) decrease plasma lactate and increase hepatic glycogen, (ii) reduce hepatic gluconeogenesis, (iii) enhance hepatic lipogenic activity and lipid secretion, (iv) led fish to double triglyceride content in muscle and to stimulate its lipid oxidative capacity, and (v) increase the content of monounsaturated fatty acids and the omega-3 alpha-linolenic acid in muscle. This study demonstrates that both microalgae-based products are suited to improve feed efficiency and orchestrate significant changes in the intermediary metabolism in gilthead seabream juveniles.

Regulation of growth, intestinal microflora composition and expression of immune-related genes by dietary supplementation of Streptococcus faecalis in blunt snout bream (Megalobrama amblycephala)

A 10-week feeding trial was performed to investigate the effects of Streptococcus faecalis on the growth, intestinal microflora composition and expression of immune-related genes of blunt snout bream (Megalobrama amblycephala). Fish (46.32 ± 0.09 g) were fed four experimental diets containing 0 cfu/g (SF0, control), 1 × 10⁵ cfu/g (SF1), 1 × 10⁶ cfu/g (SF2) and 1 × 10⁷ cfu/g (SF3) of S. faecalis, respectively. Results showed that daily growth index (DGI), feed efficiency ratio (FER), plasma glucose level, plasma contents of total protein and albumin as well as intestinal serous layer (SL), muscular layer (ML), submucous layer (SML), villi thickness (VT) and lamina propria (LP) were all no significant difference among all the treatments, whereas their (except plasma albumin content and intestinal ML) relatively high values were found in the SF2 group. Meanwhile, the intake of the SF2 diets significantly increased plasma globulin content and intestinal digestive enzymes activities, the opposite was true for the activities of plasma aspartate aminotransferase (AST) and alanine transaminase (ALT). In addition, the analysis of the intestinal microbiota showed that fish fed the SF2 diet have the highest values of intestinal alpha diversity and intestinal abundances of Actinobacteria, Chlamydiae, Firmicutes, Planctomycetes, Verrucomicrobia, Clostridium and Synechococcus, while the opposite was true for intestinal abundances of Acinetobacter, Anoxybacillus, Flavobacterium, Planctomyces, Plesiomonas, Pseudomonas, Staphylococcus and Clostridium perfringens. At the molecular level, the expression levels of tumour necrosis factor α (TNF α), interleukin 1β (IL 1β) and heat shock proteins 7 (HSP 70) in head kidney and spleen were all decreased significantly with the increasing S. faecalis levels up to 1 × 10⁶ cfu/g, and then they were increased with further increasing S. faecalis levels. Overall, dietary supplementation of S. faecalis at 1 × 10⁶ cfu/g could improve the intestinal health and innate immunity of blunt snout bream.

Co-fermentation of lentils using lactic acid bacteria and Bacillus subtilis natto increases functional and antioxidant components

We identified lentil products with both nutritional value and antioxidant capacity by studying the changes of probiotics and functional substances during single fermentation with lactic acid bacteria (LAB) or co-fermentation using LAB and Bacillus subtilis natto. After fermentation, the best growth of LAB was observed in anaerobic solid-state co-fermentation, whereby the viable counts of Lactobacillus plantarum TK9 and Lactobacillus paracasei TK1501 reached 2.77 × 109 and 2.78 × 109 CFU/g, respectively. Furthermore, the total phenol and genistin content produced by the two mixed groups, respectively, increased by 0.52- and 0.66-fold, as well as 0.63- and 0.64-fold, compared with unfermented samples. Similarly, the free amino acid content increased by 0.53- and 0.49-fold, respectively. The 50% inhibitory concentrations for the radical-scavenging against 1,1-diphenyl-2-picrylhydrazyl and α-glucosidase inhibitory activity were lower following anaerobic co-fermentation. Consistently, products of anaerobic mixed solid-state fermentation had higher oxygen radical absorbance capacity. Therefore, anaerobic solid-state co-fermentation of lentils using B. subtilis natto may promote the multiplication of LAB and enhance the antioxidant activity of fermented lentil products. PRACTICAL APPLICATION: Simple and efficient food handling is more suitable for industrial production. Co-fermentation is a good method to optimize the fermentation process. Co-culture technology has high potential in terms of functionality and antioxidant capacity.

Local DNA methylation helps to regulate muscle sirtuin 1 gene expression across seasons and advancing age in gilthead sea bream (Sparus aurata)

Background

Sirtuins (SIRTs) are master regulators of metabolism, and their expression patterns in gilthead sea bream (GSB) reveal different tissue metabolic capabilities and changes in energy status. Since little is known about their transcriptional regulation, the aim of this work was to study for the first time in fish the effect of age and season on sirt gene expression, correlating expression patterns with local changes in DNA methylation in liver and white skeletal muscle (WSM).

Methods

Gene organization of the seven sirts was analyzed by BLAT searches in the IATS-CSIC genomic database (www.nutrigroup-iats.org/seabreamdb/). The presence of CpG islands (CGIs) was mapped by means of MethPrimer software. DNA methylation analyses were performed by bisulfite pyrosequencing. A PCR array was designed for the simultaneous gene expression profiling of sirts and related markers (cs, cpt1a, pgc1α, ucp1, and ucp3) in the liver and WSM of one- and three-year-old fish during winter and summer.

Results

The occurrence of CGIs was evidenced in the sirt1 and sirt3 promoters. This latter CGI remained hypomethylated regardless of tissue, age and season. Conversely, DNA methylation of sirt1 at certain CpG positions within the promoter varied with age and season in the WSM. Among them, changes at several SP1 binding sites were negatively correlated with the decrease in sirt1 expression in summer and in younger fish. Changes in sirt1 regulation match well with variations in feed intake and energy metabolism, as judged by the concurrent changes in the analyzed markers. This was supported by discriminant analyses, which identified sirt1 as a highly responsive element to age- and season-mediated changes in energy metabolism in WSM.

Conclusions

The gene organization of SIRTs is highly conserved in vertebrates. GSB sirt family members have CGI- and non-CGI promoters, and the presence of CGIs at the sirt1 promoter agrees with its ubiquitous expression. Gene expression analyses support that sirts, especially sirt1, are reliable markers of age- and season-dependent changes in energy metabolism. Correlation analyses suggest the involvement of DNA methylation in the regulation of sirt1 expression, but the low methylation levels suggest the contribution of other putative mechanisms in the transcriptional regulation of sirt1.

Effects of Enteromyxum spp. (Myxozoa) infection in the regulation of intestinal E-cadherin: Turbot against gilthead sea bream

Enteromyxoses are relevant diseases for turbot and gilthead sea bream aquaculture. The myxozoan parasites invade the intestinal mucosa, causing a cachectic syndrome associated with intestinal barrier alteration; nonetheless, their pathological impact is different. Turbot infected by Enteromyxum scophthalmi develop more severe intestinal lesions, reaching mortality rates of 100%, whereas in E. leei-infected gilthead sea bream, the disease progresses slowly, and mortality rates are lower. The mechanisms underlying the different pathogenesis are still unclear. We studied the distribution and expression changes of E-cadherin, a highly conserved protein of the adherens junctions, in the intestine of both species by immunohistochemistry and quantitative PCR, using the same immunohistochemical protocol and common primers. The regular immunostaining pattern observed in control fish turned into markedly irregular in parasitized turbot, showing an intense immunoreaction at the host-parasite interface. Nevertheless, E-cadherin gene expression was not significantly modulated in this species. On the contrary, no evident changes in the protein distribution were noticed in gilthead sea bream, whereas a significant gene downregulation occurred in advanced infection. The results contribute to the understanding of the different host-parasite interactions in enteromyxoses. Host and parasite cells appear to establish diverse relationships in these species, which could underlie the different pathological picture.

Disruption of gut integrity and permeability contributes to enteritis in a fish-parasite model: a story told from serum metabolomics

Background

In the animal production sector, enteritis is responsible for serious economic losses, and intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and animal production efficiency. The effect of enteric parasites on the gut function of teleost fish, which represent the most ancient bony vertebrates, is far from being understood. The intestinal myxozoan parasite Enteromyxum leei dwells between gut epithelial cells and causes severe enteritis in gilthead sea bream (Sparus aurata), anorexia, cachexia, growth impairment, reduced marketability and increased mortality.

Methods

This study aimed to outline the gut failure in this fish-parasite model using a multifaceted approach and to find and validate non-lethal serum markers of gut barrier dysfunction. Intestinal integrity was studied in parasitized and non-parasitized fish by immunohistochemistry with specific markers for cellular adhesion (E-cadherin) and tight junctions (Tjp1 and Cldn3) and by functional studies of permeability (oral administration of FITC-dextran) and electrophysiology (Ussing chambers). Serum samples from parasitized and non-parasitized fish were analyzed using non-targeted metabolomics and some significantly altered metabolites were selected to be validated using commercial kits.

Results

The immunodetection of Tjp1 and Cldn3 was significantly lower in the intestine of parasitized fish, while no strong differences were found in E-cadherin. Parasitized fish showed a significant increase in paracellular uptake measured by FITC-dextran detection in serum. Electrophysiology showed a decrease in transepithelial resistance in infected animals, which showed a diarrheic profile. Serum metabolomics revealed 3702 ions, from which the differential expression of 20 identified compounds significantly separated control from infected groups in multivariate analyses. Of these compounds, serum inosine (decreased) and creatine (increased) were identified as relevant and validated with commercial kits.

Conclusions

The results demonstrate the disruption of tight junctions and the loss of gut barrier function, a metabolomic profile of absorption dysfunction and anorexia, which further outline the pathophysiological effects of E. leei.

Tissue-Specific Orchestration of Gilthead Sea Bream Resilience to Hypoxia and High Stocking Density

Two different O₂ levels (normoxia: 75–85% O₂ saturation; moderate hypoxia: 42–43% O₂ saturation) and stocking densities (LD: 9.5, and HD: 19 kg/m³) were assessed on gilthead sea bream (Sparus aurata) in a 3-week feeding trial. Reduced O₂ availability had a negative impact on feed intake and growth rates, which was exacerbated by HD despite of the improvement in feed efficiency. Blood physiological hallmarks disclosed the enhancement in O₂-carrying capacity in fish maintained under moderate hypoxia. This feature was related to a hypo-metabolic state to cope with a chronic and widespread environmental O₂ reduction, which was accompanied by a differential regulation of circulating cortisol and growth hormone levels. Customized PCR-arrays were used for the simultaneous gene expression profiling of 34–44 selected stress and metabolic markers in liver, white skeletal muscle, heart, and blood cells. The number of differentially expressed genes ranged between 22 and 19 in liver, heart, and white skeletal muscle to 5 in total blood cells. Partial Least-Squares Discriminant Analysis (PLS-DA) explained [R2Y(cum)] and predicted [Q2Y(cum)] up to 95 and 65% of total variance, respectively. The first component (R2Y = 0.2889) gathered fish on the basis of O₂ availability, and liver and cardiac genes on the category of energy sensing and oxidative metabolism (cs, hif-1α, pgc1α, pgc1β, sirts 1-2-4-5-6-7), antioxidant defense and tissue repair (prdx5, sod2, mortalin, gpx4, gr, grp-170, and prdx3) and oxidative phosphorylation (nd2, nd5, and coxi) highly contributed to this separation. The second component (R2Y = 0.2927) differentiated normoxic fish at different stocking densities, and the white muscle clearly promoted this separation by a high over-representation of genes related to GH/IGF system (ghr-i, igfbp6b, igfbp5b, insr, igfbp3, and igf-i). The third component (R2Y = 0.2542) discriminated the effect of stocking density in fish exposed to moderate hypoxia by means of hepatic fatty acid desaturases (fads2, scd1a, and scd1b) and muscle markers of fatty acid oxidation (cpt1a). All these findings disclose the different contribution of analyzed tissues (liver ≥ heart > muscle > blood) and specific genes to the hypoxic- and crowding stress-mediated responses. This study will contribute to better explain and understand the different stress resilience of farmed fish across individuals and species.

Aroclor 1254 inhibits vasotocinergic pathways related to osmoregulatory and stress functions in the gilthead sea bream (Sparus aurata, Linnaeus 1758)

The present study assesses the response of vasotocinergic system in the gilthead sea bream (Sparus aurata) after administering two doses of the polychlorinated biphenyl Aroclor 1254 (15 or 50 μg g^-1 fresh body mass). Seven days post-administration, eight fish of each experimental group were sampled, and the remaining animals were challenged with a hyperosmotic stress by being transferred from seawater (36 ppt) to high salinity water (55 ppt) and being sampled 3 days post-transfer. Aroclor 1254 affected gene expression of avt, together with Avt concentrations in pituitary and plasma, inhibiting the stimulation observed in vasotocinergic system after hyperosmotic challenge. This was noted by the accumulation of Avt at hypophyseal level as well as by its undetectable values in plasma. Hyperosmotic transfer significantly changed branchial avtrv1a, avtrv2, atp1a and cftr mRNA expression levels in control fish, while in Aroclor 1254-treated fish they remained mostly unchanged. This desensitization also occurred for avtrs in hypothalamus, caudal kidney and liver. In addition, an enhancement in plasma cortisol concentration, together with the orchestration of several players of the Hypothalamic-Pituitary-Interrenal axis (crh, crhbp, trh, star), was also observed mostly at the highest dose used (50 μg g^-1 body mass), affecting plasma and hepatic metabolites. Our results demonstrated that Aroclor 1254 compromises the hypoosmoregulatory function of vasotocinergic system in S. aurata, also inducing a concomitant stress response. In summary, this study demonstrates that Aroclor 1254 can be considered an important endocrine disruptor in relation with the correct arrangement of vasotocinergic, metabolic and stress pathways after their stimulation by transfer to hyperosmotic environments.

Effect of a specific composition of short- and medium-chain fatty acid 1-Monoglycerides on growth performances and gut microbiota of gilthead sea bream (Sparus aurata)

In aquaculture research, one important aim of gut microbiota studies is to provide the scientific basis for developing effective strategies to manipulate gut microbial communities through the diet, promoting fish health and improving productivity. Currently, there is an increasing commercial and research interest towards the use of organic acids in aquafeeds, due to several beneficial effects they have on growth performance and intestinal tract's health of farmed fish. Among organic acids, monoglycerides of short-chain fatty acids (SCFAs) and medium-chain fatty acids (MCFAs) have attracted particular research attention also for their bacteriostatic and bactericidal properties. Accordingly, the present study aimed to evaluate the potential beneficial effects of SCFA and MCFA monoglycerides, used as a feed additive, on fish growth performance, and intestinal microbiota composition. For this purpose, a specific combination of short- and medium-chain 1-monoglycerides (SILOhealth 108Z) was tested in 600 juvenile gilthead sea bream (Sparus aurata) of about 60 g mean initial weight that were fed for 90 days with plant-based diets. Two isoproteic and isolipidic diets were formulated. The control fish group received a plant-based diet, whereas the other group received the same control feed, but supplemented with 0.5% of SILOhealth 108Z. The Illumina MiSeq platform for high-throughput amplicon sequencing of 16S rRNA gene and QIIME pipeline were used to analyse and characterize the whole microbiome associated both to feeds and S. aurata intestine. The number of reads taxonomically classified according to the Greengenes database was 394,611. We identified 259 OTUs at 97% identity in sea bream fecal samples; 90 OTUs constituted the core gut microbiota. Firmicutes, Proteobacteria and Actinobacteria represented the dominant phyla in both experimental groups. Among them, relative abundance of Firmicutes and Proteobacteria were positively and negatively affected by dietary SCFA monoglycerides supplementation, respectively. In summary, our findings clearly indicated that SILOhealth 108Z positively modulated the fish intestinal microbiota by increasing the number of beneficial lactic acid bacteria, namely, Lactobacillus, and reducing Gammaproteobacteria, which include several potential pathogenic bacteria. The specific composition of 1-monoglycerides of short- and medium-chain fatty acids contained in SILOhealth 108Z could thus have a great potential as a feed additive in aquaculture.

Co-expression Analysis of Sirtuins and Related Metabolic Biomarkers in Juveniles of Gilthead Sea Bream (Sparus aurata) With Differences in Growth Performance

Sirtuins (SIRTs) represent a conserved protein family of deacetylases that act as master regulators of metabolism, but little is known about their roles in fish and livestock animals in general. The present study aimed to assess the value of SIRTs for the metabolic phenotyping of fish by assessing their co-expression with a wide-representation of markers of energy and lipid metabolism and intestinal function and health in two genetically different gilthead sea bream strains with differences in growth performance. Fish from the fast-growing strain exhibited higher feed intake, feed efficiency and plasma IGF-I levels, along with higher hepatosomatic index and lower mesenteric fat (lean phenotype). These observations suggest differences in tissue energy partitioning with an increased flux of fatty acids from adipose tissue toward the liver. The resulting increased risk of hepatic steatosis may be counteracted in the liver by reduced lipogenesis and enhanced triglyceride catabolism, in combination with a higher and more efficient oxidative metabolism in white skeletal muscle. These effects were supported by co-regulated changes in the expression profile of SIRTs (liver, sirt1; skeletal muscle, sirt2; adipose tissue, sirt5-6) and markers of oxidative metabolism (pgc1α, cpt1a, cs, nd2, cox1), mitochondrial respiration uncoupling (ucp3) and fatty acid and triglyceride metabolism (pparα, pparγ, elovl5, scd1a, lpl, atgl) that were specific to each strain and tissue. The anterior intestine of the fast-growing strain was better suited to cope with improved growth by increased expression of markers of nutrient absorption (fabp2), epithelial barrier integrity (cdh1, cdh17) and immunity (il1β, cd8b, lgals1, lgals8, sIgT, mIgT), which were correlated with low expression levels of sirt4 and markers of fatty acid oxidation (cpt1a). In the posterior intestine, the fast-growing strain showed a consistent up-regulation of sirt2, sirt3, sirt5 and sirt7 concurrently with increased expression levels of markers of cell proliferation (pcna), oxidative metabolism (nd2) and immunity (sIgT, mIgT). Together, these findings indicate that SIRTs may play different roles in the regulation of metabolism, inflammatory tone and growth in farmed fish, arising as powerful biomarkers for a reliable metabolic phenotyping of fish at the tissue-specific level.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.