Dietary Mannan Oligosaccharides: Counteracting the Side Effects of Soybean Meal Oil Inclusion on European Sea Bass (Dicentrarchus labrax) Gut Health and Skin Mucosa Mucus Production?

Prebiotics, Probiotics and Postbiotics: The Changing Paradigm of Functional Foods

The rampant use of antibiotics has led to the emergence of multidrug resistance and is often coupled with gut dysbiosis. To circumvent the harmful impact of antibiotics, probiotics have emerged as an effective intervention. However, while the new probiotics are being added to the list, more recently, the nature and role of their counterparts, viz. prebiotics, postbiotics and parabiotics have also drawn considerable attention. As such, intricate relationships among these gut-biotics vis-à-vis their role in imparting health benefits is to be delineated in a holistic manner. Prebiotic dietary fibers are selectively fermented by probiotics and promote their colonization in the gut. The proliferation of probiotics leads to production of fermentation by-products (postbiotics) which affect the growth of enteropathogens by lowering the pH and producing inhibitory bacteriocins. After completing life-cycle, their dead remnants (parabiotics e.g. exopolysaccharides and cell wall glycoproteins) also inhibit adhesion and biofilm formation of pathogens on the gut epithelium. These beneficial effects are not just endemic to gut but a systemic response is witnessed at different gut-organ axes. Thus, to decipher the role of probiotics, it is imperative to unravel the interdependence between these components. This review elaborates on the recent advancements on various aspects of these gut-biotics and the mechanism of potential attributes like anti-oxidant, anti-inflammatory, anti-neoplastic, anti-lipidemic and anti-hyperglycemic benefits.

Dietary kelp meal improves serum antioxidants, intestinal immunity, and lipid metabolism in hybrid snakehead (Channa maculata ♀ × Channa argus ♂)

BACKGROUND

Dietary kelp possesses a variety of useful biological qualities but does not have a toxic effect on the host. In this study, we examine how kelp dietary supplementation enhances the serum biochemistry, intestinal immunity, and metabolism of hybrid snakehead. A total of 810 juvenile hybrid snakeheads (Channa maculata ♀ × Channa argus ♂), with an initial average weight of 11.4 ± 0.15 g, were allocated randomly to three treatment groups (three replicates per group). The fish were fed for 60 days with isonitrogenous and isolipidic diets. The groups were the control group (C) (20% high-gluten flour), the medium replacement group (MR) (10% high-gluten flour and 10% kelp meal), and the full replacement group (FR) (0% high-gluten flour and 15% kelp meal).

RESULTS

The results showed that dietary kelp increased the activity of serum antioxidant enzymes significantly and decreased the content of serum malondialdehyde (MDA) in hybrid snakeheads, with significant changes in the FR group (P < 0.05). The intestinal morphology results showed that dietary kelp helped to increase the specific surface area of intestinal villi, which was beneficial for intestinal digestion and absorption. According to transcriptome and quantitative real-time polymerase chain reaction (qRT-PCR) analysis, dietary kelp can improve the expression of intestinal immunity and metabolism-related pathways. Among them, immune-related genes MHC1 and HSPA1 were significantly up-regulated, and IGH, MHC2, and IL-8 were significantly down-regulated (P < 0.05). Lipid metabolism-related genes DGAT2, FABP2, RXRα, and PLPP1 were all significantly up-regulated (P < 0.05).

CONCLUSION

Dietary kelp can effectively improve the antioxidant function of hybrid snakeheads, improve intestinal morphology, reduce intestinal inflammation, and promote intestinal lipid synthesis and transportation, thereby improving intestinal immunity and metabolic functions. © 2024 Society of Chemical Industry.

Cloning, expression and functional characterization of recombinant tumor necrosis factor α1 (TNFα1) from white crucian carp in gut immune regulation

TNFα is one of important cytokines belonging to TNF superfamily, which can exhibit a pleiotropic effect in immune modulation, homeostasis as well as pathogenesis. However, its immunoregulatory function on mucosal immunity in fish gut are still unclear. In this study, we aimed to investigated the immunoregulatory role of TNFα1 in midgut of white crucian carp (WCC). WCC-TNFα1 sequence and its deduced structure were firstly identified in WCC. Then, tissue-specific analysis revealed that high-level WCC-TNFα1 expression was detected in gill. After Aeromonas hydrophila and lipopolysaccharide (LPS) stimulated, increased trends of WCC-TNFα1 expressions were detected in immune-related tissues and cultured fish cells, respectively. WCC anal-intubated with WCC-TNFα1 fusion protein showed the increased levels of edema and fuzzy appearance in impaired villi, along with atrophy and reduction of goblet cells (GC). Moreover, the expression levels of tight junction (TJ) genes and mucin genes were consistently lower than those of the control (P < 0.05). WCC-TNFα1 treatment could sharply decrease antioxidant status in midgut, while the expression levels of caspase (CASP) genes, unfolded protein response (UPR) genes and redox response genes increased dramatically. Our results suggested that WCC-TNFα1 could exhibit a detrimental effect on antioxidant and mucosal immune regulation in midgut of WCC.

Effects of fermented soybean meal substitution for fish meal on intestinal flora and intestinal health in pearl gentian grouper

This study explored the role of replacing fish meal protein with fermented soybean meal (FSBM) protein on the growth performance and intestinal morphology, immunity, and microbiota of the pearl gentian grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂). Three isonitrogenous and isolipidic diets with increasing levels of FSBM (0%, 20% and 40%; referred to as FM, FSBM20 and FSBM40 diets, respectively) as a replacement for fish meal were selected for this study. The pearl gentian grouper were fed these diets for 10 weeks. The findings revealed that the growth of fish fed the FSBM diets (FSBM20 and FSBM40) were remarkably lower than the fish fed the FM diet. Pathological manifestations of intestinal inflammation, such as shortened intestinal mucosal folds and thickened lamina propria, were observed in the fish fed the FSBM diets. Moreover, the gene expression levels of IL1β, IL12, IL17, and TNFα were remarkably upregulated in fish fed the FSBM40 diet, in contrast to the gene expression levels of IL4, IL5, IL10, and TGFβ1, which were remarkably downregulated (p < 0.05). The FSBM diets significantly affected the stability of the fish gut microbiota. Photobacterium was the dominant phylum in all experimental groups, and the proportion of these bacteria gradually decreased with increasing FSBM substitution. The composition of intestinal flora at the genus level was not the same in the three experimental groups, with a richer composition of intestinal bacteria detected in the FSBM20 and FSBM40 groups (p < 0.05). The correlation between intestinal flora balance and immune gene expression revealed that only Photobacterium was negatively correlated with the above upregulated genes, while other bacteria were positively correlated with these pro-inflammatory factors (p < 0.05). Photobacterium was positively correlated with the above downregulated genes, while other bacteria were negatively correlated with these anti-inflammatory factors (p < 0.05). In conclusion, high levels of substitution of FSBM for fish meal causes intestinal inflammation in pearl gentian grouper. This is likely associated with changes to the intestinal flora. More attention should be paid to the negative role of dietary FSBM on intestinal flora.

Gut-liver immune and redox response in hybrid fish (Carassius cuvieri ♀ × Carassius auratus red var. ♂) after gut infection with Aeromonas hydrophila

Aeromonas hydrophila can pose a great threat to fish survival. In this study, we investigated the differential immune and redox response in gut-liver axis of hybrid fish (WR) undergoing gut infection. WR anally intubated with A. hydrophila showed severe midgut injury with decreased length-to-width ratios of villi along with GC hyperplasia and enhanced antioxidant activities, but expression profiles of cytokines, chemokines, antibacterial molecules, redox sensors and tight junction proteins decreased dramatically. In contrast, immune-related gene expressions and antioxidant activities increased significantly in liver of WR following gut infection with A. hydrophila. These results highlighted the differential immune regulation and redox balance in gut-liver axis response to bacterial infection.

Dietary mannan oligosaccharides strengthens intestinal immune barrier function via multipath cooperation during Aeromonas Hydrophila infection in grass carp (Ctenopharyngodon Idella)

In recent years, mannose oligosaccharide (MOS) as a functional additive is widely used in aquaculture, to enhance fish immunity. An evaluation of the effect of dietary MOS supplementation on the immune barrier function and related signaling molecules mechanism of grass carp (Ctenopharyngodon idella) was undertaken in the present study. Six diets with graded amounts of MOS supplementation (0, 200, 400, 600, 800, and 1000 mg/kg) were fed to 540 grass carp over 60 days. To examine the immune response and potential mechanisms of MOS supplementation on the intestine, a challenge test was conducted using injections of Aeromonas hydrophila for 14 days. Results of the study on the optimal supplementation with MOS were found as follows (1) MOS enhances immunity partly related to increasing antibacterial substances content and antimicrobial peptides expression; (2) MOS attenuates inflammatory response partly related to regulating the dynamic balance of intestinal inflammatory cytokines; (3) MOS regulates immune barrier function may partly be related to modulating TLRs/MyD88/NFκB and TOR/S6K1/4EBP signalling pathways. Finally, the current study concluded that MOS supplementation could improve fish intestinal immune barrier function under Aeromonas hydrophila infected conditions.

The supplementation of a prebiotic improves the microbial community in the gut and the skin of Atlantic salmon (Salmo salar)

Aquaculture growth is hindered by an increasing number of challenges, primarily infectious diseases and inappropriate or unsustainable fish nutrition. Hence it is critical to develop novel prevention strategies to minimise infectious diseases and pharmaceutical interventions. Nutritional challenges and the health of the fish could be improved by managing their microbial communities. Microbiomes can play a crucial role in fish physiology, particularly in digestion, by metabolizing largely indigestible feed components for the host or synthesis essential micronutrients. Beyond their nutritional role, microbiomes are considered the first line of defence against pathogens. In this study, a novel prebiotic mix (Selectovit), composed of 1,3/1,6-beta glucans, mannan-oligosaccharides, nucleic acids, nucleotides, medium chain fatty acids and single chain fatty acids, was tested at different inclusion levels (0.0; 0.5; 1.0; 2.0 g/kg) in the diet of Atlantic salmon (Salmo salar). Using experimental feed trials and 16 S rRNA microbiome profiling, the impact of the prebiotic blend on fish growth and microbial community within both the gastrointestinal tract and the skin was assessed. Overall, the supplement showed no significant impact on growth. However, we clearly demonstrate that the prebiotic can significantly manipulate the microbial community of the distal intestine and the skin. Several potential beneficial bacteria such as Bacillus and Mycoplasma spp. were significantly more abundant in the prebiotic-fed groups compared to the control. In contrast, putative pathogenic bacteria were less abundant in the salmon fed the prebiotic blend. Interestingly, the supplement induced more changes in the skin than in the gut. There is growing evidence in fish for highly complex interactions between the microbial communities of the digestive system and external mucosa, and with the host immune system. Further research in this field could lead to the creation of novel bacterial biomarkers and new non-invasive strategies for fish digestive health monitoring.

Deploying an In Vitro Gut Model to Assay the Impact of the Mannan-Oligosaccharide Prebiotic Bio-Mos on the Atlantic Salmon (Salmo salar) Gut Microbiome

Alpha mannose-oligosaccharide (MOS) prebiotics are widely deployed in animal agriculture as immunomodulators as well as to enhance growth and gut health. Their mode of action is thought to be mediated through their impact on host microbial communities and their associated metabolism. Bio-Mos is a commercially available prebiotic currently used in the agri-feed industry, but studies show contrasting results of its effect on fish performance and feed efficiency. Thus, detailed studies are needed to investigate the effect of MOS supplements on the fish microbiome to enhance our understanding of the link between MOS and gut health. To assess Bio-Mos for potential use as a prebiotic growth promoter in salmonid aquaculture, we have modified an established Atlantic salmon in vitro gut model, SalmoSim, to evaluate its impact on the host microbial communities. The microbial communities obtained from ceca compartments from four adult farmed salmon were inoculated in biological triplicate reactors in SalmoSim. Prebiotic treatment was supplemented for 20 days, followed by a 6-day washout period. Inclusion of Bio-Mos in the media resulted in a significant increase in formate (P = 0.001), propionate (P = 0.037) and 3-methyl butanoic acid (P = 0.024) levels, correlated with increased abundances of several, principally, anaerobic microbial genera (Fusobacterium, Agarivorans, Pseudoalteromonas). DNA metabarcoding with the 16S rDNA marker confirmed a significant shift in microbial community composition in response to Bio-Mos supplementation with observed increase in lactic acid producing Carnobacterium. In conjunction with previous in vivo studies linking enhanced volatile fatty acid production alongside MOS supplementation to host growth and performance, our data suggest that Bio-Mos may be of value in salmonid production. Furthermore, our data highlights the potential role of in vitro gut models to complementin vivo trials of microbiome modulators. IMPORTANCE In this paper we report the results of the impact of a prebiotic (alpha-MOS supplementation) on microbial communities, using an in vitro simulator of the gut microbial environment of the Atlantic salmon. Our data suggest that Bio-Mos may be of value in salmonid production as it enhances volatile fatty acid production by the microbiota from salmon pyloric ceca and correlates with a significant shift in microbial community composition with observed increase in lactic acid producing Carnobacterium. In conjunction with previous in vivo studies linking enhanced volatile fatty acid production alongside MOS supplementation to host growth and performance, our data suggest that Bio-Mos may be of value in salmonid production. Furthermore, our data highlights the potential role of in vitro gut models to augment in vivo trials of microbiome modulators.

Dietary Mannan Oligosaccharides Enhance the Non-Specific Immunity, Intestinal Health, and Resistance Capacity of Juvenile Blunt Snout Bream (Megalobrama amblycephala) Against Aeromonas hydrophila

Mannan oligosaccharides (MOS) have been studied and applied as a feed additive, whereas their regulation on the growth performance and immunity of aquatic animals lacks consensus. Furthermore, their immunoprotective effects on the freshwater fish Megalobrama amblycephala have not been sufficiently studied. Thus, we investigated the effects of dietary MOS of 0, 200, and 400 mg/kg on the growth performance, non-specific immunity, intestinal health, and resistance to Aeromonas hydrophila infection in juvenile M. amblycephala. The results showed that the weight gain rate of juvenile M. amblycephala was not significantly different after 8 weeks of feeding, whereas the feed conversion ratio decreased in the MOS group of 400 mg/kg. Moreover, dietary MOS increased the survival rate of juvenile M. amblycephala upon infection, which may be attributed to enhanced host immunity. For instance, dietary MOS increase host bactericidal and antioxidative abilities by regulating the activities of hepatic antimicrobial and antioxidant enzymes. In addition, MOS supplementation increased the number of intestinal goblet cells, and the intestine was protected from necrosis of the intestinal folds and disruption of the microvilli and junctional complexes, thus maintaining the stability of the intestinal epithelial barrier. The expression levels of M. amblycephala immune and tight junction-related genes increased after feeding dietary MOS for 8 weeks. However, the upregulated expression of immune and tight junction-related genes in the MOS supplemental groups was not as notable as that in the control group postinfection. Therefore, MOS supplementation might suppress the damage caused by excessive intestinal inflammation. Furthermore, dietary MOS affected the richness and composition of the gut microbiota, which improved the gut health of juvenile M. amblycephala by increasing the relative abundance of beneficial gut microbiota. Briefly, dietary MOS exhibited significant immune protective effects to juvenile M. amblycephala, which is a functional feed additive and immunostimulant.

Functional feeds marginally alter immune expression and microbiota of Atlantic salmon (Salmo salar) gut, gill, and skin mucosa though evidence of tissue-specific signatures and host-microbe coadaptation remain

Background

Mucosal surfaces of fish provide cardinal defense against environmental pathogens and toxins, yet these external mucosae are also responsible for maintaining and regulating beneficial microbiota. To better our understanding of interactions between host, diet, and microbiota in finfish and how those interactions may vary across mucosal tissue, we used an integrative approach to characterize and compare immune biomarkers and microbiota across three mucosal tissues (skin, gill, and gut) in Atlantic salmon receiving a control diet or diets supplemented with mannan-oligosaccharides, coconut oil, or both. Dietary impacts on mucosal immunity were further evaluated by experimental ectoparasitic sea lice (Lepeophtheirus salmonis) challenge.

Results

Fish grew to a final size of 646.5 g ± 35.8 during the 12-week trial, with no dietary effects on growth or sea lice resistance. Bacterial richness differed among the three tissues with the highest richness detected in the gill, followed by skin, then gut, although dietary effects on richness were only detected within skin and gill. Shannon diversity was reduced in the gut compared to skin and gill but was not influenced by diet. Microbiota communities clustered separately by tissue, with dietary impacts on phylogenetic composition only detected in the skin, although skin and gill communities showed greater overlap compared to the gut according to overall composition, differential abundance, and covariance networks. Inferred metagenomic functions revealed preliminary evidence for tissue-specific host–microbiota coadaptation, as putative microbiota functions showed ties to the physiology of each tissue. Immune gene expression profiles displayed tissue-specific signatures, yet dietary effects were also detected within each tissue and peripheral blood leukocytes. Procrustes analysis comparing sample-matched multivariate variation in microbiota composition to that of immune expression profiles indicated a highly significant correlation between datasets.

Conclusions

Diets supplemented with functional ingredients, namely mannan-oligosaccharide, coconut oil, or a both, resulted in no difference in Atlantic salmon growth or resistance to sea lice infection. However, at the molecular level, functional ingredients caused physiologically relevant changes to mucosal microbiota and host immune expression. Putative tissue-specific metagenomic functions and the high correlation between expression profiles and microbiota composition suggest host and microbiota are interdependent and coadapted in a tissue-specific manner.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-022-00173-0.

Mannan Oligosaccharides Application: Multipath Restriction From Aeromonas hydrophila Infection in the Skin Barrier of Grass Carp (Ctenopharyngodon idella)

The objective of this study was to evaluate the efficacy of dietary Mannan oligosaccharides (MOS) supplementation on skin barrier function and the mechanism of on-growing grass carp (Ctenopharyngodon idella). Five hundred forty grass carp were fed for 60 days from the growing stage with six different levels of MOS diets (0, 200, 400, 600, 800, and 1,000 mg kg^-1). At the end of the growth trial, the 14-day Aeromonas hydrophila challenge experiment has proceeded. The obtained data indicate that MOS could (1) decline skin lesion morbidity after being challenged by the pathogenic bacteria; (2) maintain physical barrier function via improving antioxidant ability, inhibiting excessive apoptosis, and strengthening the tight junction between the epithelial cell and the related signaling pathway (Nrf2/Keap1, p38MAPK, and MLCK); and (3) regulate immune barrier function by modulating the production of antimicrobial compound and expression of involved cytokines and the related signaling pathway (TOR and NFκB). Finally, we concluded that MOS supplementation reinforced the disease resistance and protected the fish skin barrier function from Aeromonas hydrophila infection.

Nutrient Digestibility, Growth, Mucosal Barrier Status, and Activity of Leucocytes From Head Kidney of Atlantic Salmon Fed Marine- or Plant-Derived Protein and Lipid Sources

Nutrient digestibility, growth, and mucosal barrier status of fish skin, gills, and distal intestine were studied in Atlantic salmon fed feeds based on marine or plant-derived ingredients. The barrier status was assessed by considering the expression of four mucin genes, five genes that encode antimicrobial proteins, distal intestine micromorphology, and design-based stereology of the midgut epithelium. In addition, the head kidney leukocytes were examined using flow cytometry; to understand the differences in their counts and function. Five experimental feeds containing the main components i) fishmeal and fish oil (BG1), ii) soybean meal (BG2; to induce enteritis), iii) fishmeal as the main protein source and rapeseed oil as the main lipid source (BG3), iv) a mix of plant protein concentrates as the protein sources and fish oil as the lipid source (BG4), and v) plant and marine ingredients in the ratio 70:30 (BG5) were produced for the study. Atlantic salmon with initial weight 72.7 ± 1.2 g was offered the experimental feeds for 65 days. The results revealed that the weights of all fish groups doubled, except for fish fed BG2. Fish fed the BG2 diet had lower blood cholesterol concentration, developed enteritis, had lower expression of muc2 in the distal intestine, and had a compromised barrier status in the intestine. Expression of both the mucin genes and genes that encode antimicrobial peptides were tissue-specific and some were significantly affected by diet. The fish fed BG1 and BG3 had more head kidney lymphocyte-like cells compared to BG5-fed fish, and the phagocytic activity of macrophage-like cells from the head kidney was the highest in fish fed BG1. The intestinal micromorphology and the mucosal mapping suggest two different ways by which plant-based diets can alter the gut barrier status; by either reducing the mucous cell sizes, volumetric densities and barrier status (as noted for BG2) or increasing volumetric density of mucous cells (as observed for BG4 and BG5). The results of the compromised intestinal barrier in fish fed plant ingredients should be further confirmed through transcriptomic and immunohistochemical studies to refine ingredient composition for sustainable and acceptable healthy diets.

Histological mucous cell quantification and mucosal mapping reveal different aspects of mucous cell responses in gills and skin of shorthorn sculpins (Myoxocephalus scorpius)

In teleosts, the mucosal epithelial barriers represent the first line of defence against environmental challenges such as pathogens and environmental contaminants. Mucous cells (MCs) are specialised cells providing this protection through mucus production. Therefore, a better understanding of various MC quantification methods is critical to interpret MC responses. Here, we compare histological (also called traditional) quantification of MCs with a novel mucosal mapping method to understand the differences between the two methods' assessment of MC responses to parasitic infections and pollution exposure in shorthorn sculpins (Myoxocephalus scorpius). Overall, both methods distinguished between the fish from stations with different levels of pollutants and detected the links between MC responses and parasitic infection. Traditional quantification showed relationship between MC size and body size of the fish whereas mucosal mapping detected a link between MC responses and Pb level in liver. While traditional method gave numerical density, mucosal mapping gave volumetric density of the mucous cells in the mucosa. Both methods differentiated MC population in skin from those in the gills, but only mucosal mapping pointed out the consistent differences between filament and lamellar MC populations within the gills. Given the importance of mucosal barriers in fish, a better understanding of various MC quantification methods and the linkages between MC responses, somatic health and environmental stressors is highly valuable.

V, Izquierdo M, Terova G. Assessment of dietary supplementation with galactomannan oligosaccharides and phytogenics on gut microbiota of European sea bass (Dicentrarchus Labrax) fed low fishmeal and fish oil based diet

There is an increasing interest from the aquafeed industry in functional feeds containing selected additives that improve fish growth performance and health status. Functional feed additives include probiotics, prebiotics, organic acids, and phytogenics (substances derived from plants and their extracts). This study evaluated the effects of dietary inclusion of a mucilage extract rich in galactomannan oligosaccharides (GMOS), a mixture of garlic and labiatae-plants oils (PHYTO), and a combination of them (GMOSPHYTO), on gut microbiota composition of European sea bass (Dicentrarchus labrax) fed with a low fishmeal (FM) and fish oil (FO) diet. Three experimental diets and a control diet (plant-based formulation with 10% FM and 6% FO) were tested in a 63-days feeding trial. To analyze the microbiota associated to feeds and the intestinal autochthonous (mucosa-adhered) and allochthonous (transient) microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and QIIME2 pipeline were used. Metabarcoding analysis of feed-associated bacteria showed that the microbial communities of control (CTRL) feed deeply differed from those of experimental diets. The number of reads was significantly lower in CTRL feed than in other feeds. The OTU (operational taxonomic unit) number was instead similar between the feeds, ranging from 42 to 50 OTUs. The variation of resident gut microbiota induced by diet was lower than the variation of transient intestinal microbiota, because feedstuffs are a major source of allochthonous bacteria, which can temporarily integrate into the gut transient microbiome. However, the composition of transient bacterial communities was not simply a mirror of feed-borne bacteria. Indeed, the microbial profile of feeds was different from both faecal and mucosa profiles. Our findings suggest that the dietary inclusion of GMOS (0.5%) and PHYTO (0.02%) in a low FM and FO diet induces changes in gut microbiota composition of European sea bass. However, if on allochthonous microbiota the combined inclusion of GMOS and PHYTO showed an antagonistic effect on bactericidal activity against Vibrionales, at mucosa level, only GMOSPHYTO diet increased the relative abundance of Bacteroidales, Lactobacillales, and Clostridiales resident bacterial orders. The main beneficial effects of GMOS and PHYTO on gut microbiota are the reduction of coliforms and Vibrionales bacteria, which include several potentially pathogenic species for fish, and the enrichment of gut microbiota composition with butyrate producer taxa. Therefore, these functional ingredients have a great potential to be used as health-promoting agents in the farming of European sea bass and other marine fish.

Probiotic Effects of a Novel Strain, Acinetobacter KU011TH, on the Growth Performance, Immune Responses, and Resistance against Aeromonas hydrophila of Bighead Catfish (Clarias macrocephalus Günther, 1864)

In the present study, the novel probiotic strain Acinetobacter KU011TH with an evident lack of pathogenicity in catfish was experimented. Three practical administration routes, namely, feed additive (FD), water-soluble additive (SOL), and a combination route (FD+SOL), were applied in two sizes of catfish. After 120 days of FD+SOL administration, catfish fingerlings (15 g) exhibited a significant improvement in all tested growth performance parameters. For 15- and 30-day applications at the juvenile stage (150 g), phagocytic activity, phagocytic index, lysozyme activity, respiratory burst activity, alternative complement pathway, and bactericidal activity were significantly increased. Furthermore, probiotic-administered bighead catfish exhibited an upregulated expression of several immune-related genes in tested organs. Significant colonization by Acinetobacter KU011TH in rearing water and on skin and gills was observed among experimental groups. Histological analysis clearly indicated enhanced physical characteristics of skin mucosal immunity in the treated groups. No histopathological changes in the gills, skin, intestine or liver were observed among the fish groups. Interestingly, after challenge with Aeromonas hydrophila, the survival rates of the treated groups were significantly higher than those of the controls. In conclusion, the novel probiont Acinetobacter KU011TH provides a potent strategy for improvement in growth and disease resistance, which is an important steppingstone for sustaining catfish aquaculture.

Dietary phytogenics and galactomannan oligosaccharides in low fish meal and fish oil-based diets for European sea bass (Dicentrarchus labrax) juveniles: Effects on gut health and implications on in vivo gut bacterial translocation

European sea bass were fed four low FM/FO (10%/6%) diets containing galactomannan oligosaccharides (GMOS), a mixture of garlic oil and labiatae plants oils (PHYTO), or a combination of both functional products (GMOSPHYTO) for 63 days before exposing the fish to an intestinal Vibrio anguillarum infection combined with crowding stress. In order to evaluate functional diets efficacy in terms of gut health maintenance, structural, cellular, and immune intestinal status were evaluated by optical and electron microscopy and gene expression analyses. A semi-automated software was adapted to determine variations in goblet cell area and mucosal mucus coverage during the challenge test. Feeding with functional diets did not affect growth performance; however, PHYTO and GMOS dietary inclusion reduced European sea bass susceptibility to V. anguillarum after 7 days of challenge testing. Rectum (post-ileorectal valve) showed longer (p = 0.001) folds than posterior gut (pre-ileorectal valve), whereas posterior gut had thicker submucosa (p = 0.001) and higher mucus coverage as a result of an increased cell density than rectum. Functional diets did not affect mucosal fold length or the grade of granulocytes and lymphocytes infiltration in either intestinal segment. However, the posterior gut fold area covered by goblet cells was smaller in fish fed GMOS (F = 14.53; p = 0.001) and PHYTO (F = 5.52; p = 0.019) than for the other diets. PHYTO (F = 3.95; p = 0.049) reduced posterior gut goblet cell size and increased rodlet cell density (F = 3.604; p = 0.068). Dietary GMOS reduced submucosal thickness (F = 51.31; p = 0.001) and increased rodlet cell density (F = 3.604; p = 0.068) in rectum. Structural TEM analyses revealed a normal intestinal morphological pattern, but the use of GMOS increased rectum microvilli length, whereas the use of PHYTO increased (p≤0.10) Ocln, N-Cad and Cad-17 posterior gut gene expression. After bacterial intestinal inoculation, posterior gut of fish fed PHYTO responded in a more controlled and belated way in terms of goblet cell size and mucus coverage in comparison to other treatments. For rectum, the pattern of response was similar for all dietary treatments, however fish fed GMOS maintained goblet cell size along the challenge test.

Mucous cell responses to contaminants and parasites in shorthorn sculpins (Myoxocephalus scorpius) from a former lead‑zinc mine in West Greenland

Previous studies of sculpins from the former lead (Pb) - zinc (Zn) mine near Maarmorilik, West Greenland, have shown that these fish are affected by heavy metal exposure from the mine. In this study, we applied mucosal mapping (a stereological method for mucosal quantification in fish) to uncover interactions between the host, parasites and heavy metal exposure (Pb and Zn) in shorthorn sculpins from the Maarmorilik mining site at a gradient of 3 stations. Skin and gill mucosal epithelia of shorthorn sculpins were significantly affected and reflected the exposure to environmental heavy metals and parasites. Size of skin mucous cells was significantly smallest in the sculpin from the station 3 where heavy metal contamination was lowest and the skin parasite load was highest. Gill filament mucous cells were largest and densest in fish from station 1 which was the most contaminated site. In gill lamellae the density of mucous cell followed a toxicity gradient and was significantly highest at the most contaminated station and significantly lowest at the least contaminated station. The persistent presence of toxic Pb and Zn levels in the sediment at the most contaminated station may have induced a small but measurable reduction in the surface area available for respiration and may have affected diffusion distance. The strong correlation between size of filamentous mucous cells and Pb concentrations in liver suggests that these cells can play an active role in reducing the somatic load of Pb in sculpin. We suggest that mucosal mapping can be used to assess effects of contaminant and parasite exposure in future environmental field studies.

Defatted microalgae (Nannochloropsis sp.) from biorefinery as a potential feed protein source to replace fishmeal in European sea bass diets

The present work focuses on the use of defatted biomass of the microalga Nannochloropsis sp. from the biodiesel industry, as a partial substitute of fish meal (FM) in diets for European sea bass. The effects of increasing inclusion levels of microalgal meal on growth performance, body composition, nutrient utilization, gut morphology, and innate immunity were evaluated after 93 days. A reference alga-free diet was the control (CTRL) diet, and the three experimental diets contained 5 (MA5), 10 (MA10), and 15% (MA15) of the microalgal meal. The microalga-rich diets were supplemented with DL-methionine to assure sea bass dietary requirement. Overall, nutrient apparent digestibilities (ADCs) of the diets were not altered by the microalgal inclusion, but energy ADC was highest in fish fed the CTRL diet (90% vs 88%). At the end of the trial, fish growth performance was similar among dietary treatments (DGI of 1.0), but fish fed MA10 had a significantly higher feed conversion ratio than those fed CTRL and MA5. Final whole body composition and nutrient gain of fish fed the different diets were similar. No significant differences were detected in gut morphology among treatments. Innate immune parameters (lysozyme, alternative complement pathway-ACH50, and peroxidase) were examined, and ACH50 of the fish fed MA15 was significantly lower than those fed MA10, suggesting a dose-dependent stimulation of the innate immune response. The present results indicate that defatted microalgal meal can replace fishmeal in European sea bass diets-at inclusion levels of up to 15%-contributing to a circular economy approach.

Key nutritional factors and interactions during larval development of pikeperch (Sander lucioperca)

The effects of 8 nutritional variables (Ca/P, Eicosapentaenoic acid (20:5n-3) + Docosahexaenoic acid (22:6n − 3) (EPA + DHA), Arachidonic acid (20:4n − 6) (ARA), Se, vitamins E, C, D and A) were investigated to identify their respective importance and interactions in pikeperch larval development. In this respect, two modalities (low and high levels) of each variable were tested through a fractional factorial experimental design allowing a reduction from 256 (2⁸) to 16 (2^8 – 4) experimental units. Survival was significantly higher in larvae fed a high Ca/P diet while larval growth was significantly lower in larvae fed the same diet variant, associated with a higher incidence of kyphosis and pectoral anomalies in these larvae. Lordosis and scoliosis seemed to be mostly affected by dietary long chain polyunsaturated fatty acids (LC-PUFAs). A significant interaction was shown between n-3 LC-PUFA and vitamin C on jaw anomalies, while myocyte-specific enhancer factor 2C (mef2c) gene expression correlated positively with dietary vitamin C increment. Results also demonstrated an effect of the different nutrients and their interactions on the activity levels of digestive enzymatic activities. The results of the present study highlight the importance of the interactions between Ca/P, LC-PUFAs and vitamins C and E, suggesting their essential roles as key nutritional factors influencing pikeperch larval development.

Increased parasite resistance of greater amberjack (Seriola dumerili Risso 1810) juveniles fed a cMOS supplemented diet is associated with upregulation of a discrete set of immune genes in mucosal tissues

The main objective of this study was to determine the effect of two forms of mannan oligosaccharides (MOS: Bio-Mos^® and cMOS: Actigen^®, Alltech Inc, USA) and their combination on greater amberjack (Seriola dumerili) growth performance and feed efficiency, immune parameters and resistance against ectoparasite (Neobenedenia girellae) infection. Fish were fed for 90 days with 5 g kg^-1 MOS, 2 g kg^-1 cMOS or a combination of both prebiotics, in a Seriola commercial base diet (Skretting, Norway). At the end of the feeding period, no differences were found in growth performance or feed efficiency. Inclusion of MOS also had no effect on lysozyme activity in skin mucus and serum, but the supplementation of diets with cMOS induced a significant increase of serum bactericidal activity. Dietary cMOS also reduced significantly greater amberjack skin parasite levels, parasite total length and the number of parasites detected per unit of fish surface following a cohabitation challenge with N. girellae, whereas no effect of MOS was detected on these parameters. Of 17 immune genes studied cMOS dietary inclusion up-regulated hepcidin, defensin, Mx protein, interferon-γ (IFNγ), mucin-2 (MUC-2), interleukin-1β (IL-1B), IL-10 and immunoglobulin-T (IgT) gene expression in gills and/or skin. MOS supplementation had a larger impact on spleen and head kidney gene expression, where piscidin, defensin, iNOS, Mx protein, interferons, IL-1β, IL-10, IL-17 and IL-22 were all upregulated. In posterior gut dietary MOS and cMOS both induced IL-10, IgM and IgT, but with MOS also increasing piscidin, MUC-2, and IL-1β whilst cMOS induced hepcidin, defensin and IFNγ. In general, the combination of MOS and cMOS resulted in fewer or lower increases in all tissues, possibly due to an overstimulation effect. The utilization of cMOS at the dose used here has clear benefits on parasite resistance in greater amberjack, linked to upregulation of a discrete set of immune genes in mucosal tissues.

Rainbow Trout (Oncorhynchus Mykiss) Intestinal Epithelial Cells as a Model for Studying Gut Immune Function and Effects of Functional Feed Ingredients

The objective of this study was to evaluate the suitability of the rainbow trout intestinal epithelial cell line (RTgutGC) as an in vitro model for studies of gut immune function and effects of functional feed ingredients. Effects of lipopolysaccharide (LPS) and three functional feed ingredients [nucleotides, mannanoligosaccharides (MOS), and beta-glucans] were evaluated in RTgutGC cells grown on conventional culture plates and transwell membranes. Permeation of fluorescently-labeled albumin, transepithelial electrical resistance (TEER), and tight junction protein expression confirmed the barrier function of the cells. Brush border membrane enzyme activities [leucine aminopeptidase (LAP) and maltase] were detected in the RTgutGC cells but activity levels were not modulated by any of the exposures. Immune related genes were expressed at comparable relative basal levels as these in rainbow trout distal intestine. LPS produced markedly elevated gene expression levels of the pro-inflammatory cytokines il1b, il6, il8, and tnfa but had no effect on ROS production. Immunostaining demonstrated increased F-actin contents after LPS exposure. Among the functional feed ingredients, MOS seemed to be the most potent modulator of RTgutGC immune and barrier function. MOS significantly increased albumin permeation and il1b, il6, il8, tnfa, and tgfb expression, but suppressed ROS production, cell proliferation and myd88 expression. Induced levels of il1b and il8 were also observed after treatment with nucleotides and beta-glucans. For barrier function related genes, all treatments up-regulated the expression of cldn3 and suppressed cdh1 levels. Beta-glucans increased TEER levels and F-actin content. Collectively, the present study has provided new information on how functional ingredients commonly applied in aquafeeds can affect intestinal epithelial function in fish. Our findings suggest that RTgutGC cells possess characteristic features of functional intestinal epithelial cells indicating a potential for use as an efficient in vitro model to evaluate effects of bioactive feed ingredients on gut immune and barrier functions and their underlying cellular mechanisms.

Correlations between serum amyloid A, C-reactive protein and clinical indices of patients with acutely exacerbated chronic obstructive pulmonary disease

Background

To explore the correlations between SAA, CRP, and clinical indices of patients with acutely exacerbated chronic obstructive pulmonary disease (AECOPD).

Methods

A total of 120 patients with AECOPD and another 120 with remitted COPD were enrolled in an AECOPD group and a COPD remission group, respectively. Meanwhile, 120 healthy subjects were included as a control group. SAA, CRP, PCT, Fbg, IL‐8, IL‐6, TNF‐α, and IP‐10 levels were detected. FEV₁ and FEV₁/FVC were measured.

Results

Compared with control group, the serum levels of SAA, CRP, PCT, Fbg, IL‐8, IL‐6, TNF‐α, and IP‐10 significantly increased in COPD remission group (P < 0.05). The levels of AECOPD group significantly exceeded those of COPD remission group (P < 0.05). The levels of AECOPD patients with different GOLD grades were significantly different (P < 0.05). AECOPD group had significantly lower FEV₁ and FEV₁/FVC than those of COPD remission group (P < 0.05). The CAT score of AECOPD patients was (18.41 ± 2.55) points. The levels of SAA, CRP, PCT, Fbg, IL‐8, IL‐6, TNF‐α, and IP‐10 were negatively correlated with FEV₁ and FEV₁/FVC, and positively correlated with CAT score. The area under receiver operating characteristic curve of SAA was largest (0.931). The cutoff values for SAA, CRP, PCT and Fbg were 18.68 mg/L, 14.70 mg/L, 0.39 μg/L, 3.91 g/L, 0.46 μg/L, 24.17 μg/L, 7.18 mg/L, and 83.19 ng/L, respectively.

Conclusions

Serum levels of SAA, CRP, PCT, Fbg, IL‐8, IL‐6, TNF‐α, and IP‐10 in AECOPD patients were elevated, which may undermine pulmonary functions. SAA can be used as an effective index for AECOPD diagnosis and treatment.

Use of Organic Wastes and Industrial By-Products to Produce Filamentous Fungi with Potential as Aqua-Feed Ingredients

Organic-rich waste and industrial by-product streams, generated in enormous amounts on a daily basis, contain substantial amounts of nutrients that are worthy of recovery. Biological conversion of organic-waste streams using filamentous fungi is a promising approach to convert nutrients into value-added bioproducts, such as fungal biomass. High-protein fungal biomass contains different kinds and levels of amino acids, fatty acids, immunostimulants, antioxidants, pigments, etc., which make it a potential choice for application in animal feed supplementation. Considering the challenges long faced by the aquaculture industry in fishmeal production due to the increasing prices and environmental concerns, the aquaculture industry is forced to provide alternative protein-rich sources to replace conventional fishmeal. In this review, the possibilities of utilization of filamentous fungi biomass cultivated on organic-rich waste streams, as an alternative nutrient source in fish feed, were thoroughly reviewed.

Integrative Transcriptomic and microRNAomic Profiling Reveals Immune Mechanism for the Resilience to Soybean Meal Stress in Fish Gut and Liver

In aquafeeds, fish-meal has been commonly replaced with plant protein, which often causes enteritis. Currently, foodborne enteritis has few solutions in regards to prevention or cures. The recovery mechanism from enteritis in herbivorous fish may further help understand prevention or therapy. However, few reports could be found regarding the recovery or resilience to fish foodborne enteritis. In this study, grass carp was used as an animal model for soybean meal induced enteritis and it was found that the fish could adapt to the soybean meal at a moderate level of substitution. Resilience to soybean meal stress was found in the 40% soybean meal group for juvenile fish at growth performance, morphological and gene expression levels, after a 7-week feeding trial. Furthermore, the intestinal transcriptomic data, including transcriptome and miRNAome, was applied to demonstrate resilience mechanisms. The result of this study revealed that in juvenile grass carp after a 7-week feeding cycle with 40% soybean meal, the intestine recovered via enhancing both an immune tolerance and wound healing, the liver gradually adapted via re-balancing immune responses, such as phagosome and complement cascades. Also, many immune factors in the gut and liver were systemically revealed among stages of on-setting, remising, and recovering (or relief). In addition, miRNA regulation played a key role in switching immune states. Thus, the present data systemically demonstrated that the molecular adaptation mechanism of fish gut-liver immunity is involved in the resilience to soybean meal stress.

Disease resistance and response against Vibrio anguillarum intestinal infection in European seabass (Dicentrarchus labrax) fed low fish meal and fish oil diets

The aim of this study was to assess the effects of low levels of dietary fish meal (FM) and fish oil (FO) on disease resistance and gut associated lymphoid tissue (GALT) response after an experimental intestinal infection with V. anguillarum in European sea bass (Dicentrarchus labrax) For that purpose, sea bass juveniles were fed one of four diets containing combined levels of FO and FM as follows: 20%FM/6%FO, 20%FM/3%FO, 5%FM/6%FO and 5%FM/3%FO during 153 days. At the end of the feeding trial, fish were subjected to either an in vivo exposure to a sub-lethal dose of V. anguillarum via anal inoculation or to an ex vivo exposure to V. anguillarum. Additionally, inducible nitric oxide synthase (iNOS) and tumor necrosis factor α (TNFα) gut patterns of immunopositivity were studied. Growth performance was affected by dietary FM level, however ex vivo gut bacterial translocation rates and survival after the in vivo challenge test were affected by dietary FO level. After 5 months of feeding, low dietary FM levels led to a posterior gut up-regulation of interleukin-1β (IL-1β) and TNFα, major histocompatibility complex-II (MHCII) and cyclooxygenase-2 (COX2), which in turn reduced the gut associated lymphoid tissue (GALT) capacity of response after 24 h post infection and conditioned European sea bass capacity to recover gut homeostasis 7 days post infection. Immunoreactivity to anti-iNOS and anti-TNFα presented a gradient of increased immunopositivity towards the anus, regardless of the dietary FM/FO fed. Strong positive anti-TNFα isolated enterocytes were observed in the anterior gut in relation to low levels of dietary FM/FO. Submucosa and lamina propria immunoreactivity grade was related to the amount of leucocyte populations infiltrated and goblet cells presented immunopositivity to anti-iNOS but not to anti-TNFα. Thus, reducing FO content from 6% to a 3% by VO in European sea bass diets increases ex vivo and in vivo gut bacterial translocation rates, whereas reducing FM content from 20% down to 5% up-regulates the expression of several posterior gut inflammation-related genes conditioning fish growth and GALT capacity of response after bacterial infection.

An oil containing EPA and DHA from transgenic Camelina sativa to replace marine fish oil in feeds for Atlantic salmon (Salmo salar L.): Effects on intestinal transcriptome, histology, tissue fatty acid profiles and plasma biochemistry

New de novo sources of omega 3 (n-3) long chain polyunsaturated fatty acids (LC-PUFA) are required as alternatives to fish oil in aquafeeds in order to maintain adequate levels of the beneficial fatty acids, eicosapentaenoic and docosahexaenoic (EPA and DHA, respectively). The present study investigated the use of an EPA+DHA oil derived from transgenic Camelina sativa in Atlantic salmon (Salmo salar) feeds containing low levels of fishmeal (35%) and fish oil (10%), reflecting current commercial formulations, to determine the impacts on tissue fatty acid profile, intestinal transcriptome, and health of farmed salmon. Post-smolt Atlantic salmon were fed for 12-weeks with one of three experimental diets containing either a blend of fish oil/rapeseed oil (FO), wild-type camelina oil (WCO) or transgenic camelina oil (DCO) as added lipid source. The DCO diet did not affect any of the fish performance or health parameters studied. Analyses of the mid and hindgut transcriptomes showed only mild effects on metabolism. Flesh of fish fed the DCO diet accumulated almost double the amount of n-3 LC-PUFA than fish fed the FO or WCO diets, indicating that these oils from transgenic oilseeds offer the opportunity to increase the n-3 LC-PUFA in farmed fish to levels comparable to those found a decade ago.

Replacement of Marine Fish Oil with de novo Omega-3 Oils from Transgenic Camelina sativa in Feeds for Gilthead Sea Bream (Sparus aurata L.)

Omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA) are essential components of the diet of all vertebrates. The major dietary source of n-3 LC-PUFA for humans has been fish and seafood but, paradoxically, farmed fish are also reliant on marine fisheries for fish meal and fish oil (FO), traditionally major ingredients of aquafeeds. Currently, the only sustainable alternatives to FO are vegetable oils, which are rich in C18 PUFA, but devoid of the eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) abundant in FO. Two new n-3 LC-PUFA sources obtained from genetically modified (GM) Camelina sativa containing either EPA alone (ECO) or EPA and DHA (DCO) were compared to FO and wild-type camelina oil (WCO) in juvenile sea bream. Neither ECO nor DCO had any detrimental effects on fish performance, although final weight of ECO-fed fish (117 g) was slightly lower than that of FO- and DCO-fed fish (130 and 127 g, respectively). Inclusion of the GM-derived oils enhanced the n-3 LC-PUFA content in fish tissues compared to WCO, although limited biosynthesis was observed indicating accumulation of dietary fatty acids. The expression of genes involved in several lipid metabolic processes, as well as fish health and immune response, in both liver and anterior intestine were altered in fish fed the GM-derived oils. This showed a similar pattern to that observed in WCO-fed fish reflecting the hybrid fatty acid profile of the new oils. Overall the data indicated that the GM-derived oils could be suitable alternatives to dietary FO in sea bream.