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Background: Intestinal digesta is commonly used for studying responses of microbiota to dietary shifts, yet evidence is accumulating that it represents an incomplete view of the intestinal microbiota. The present work aims to investigate the differences between digesta- and mucosa-associated intestinal microbiota in Atlantic salmon (Salmo salar) and how they may respond differently to dietary perturbations. In a 16-week seawater feeding trial, Atlantic salmon were fed either a commercially-relevant reference diet or an insect meal diet containing ~ 15% black soldier fly (Hermetia illucens) larvae meal. The digesta- and mucosa-associated distal intestinal microbiota were profiled by 16S rRNA gene sequencing. Results: Regardless of diet, we observed substantial differences between digesta- and mucosa-associated intestinal microbiota. Microbial richness and diversity were much higher in the digesta than the mucosa. The insect meal diet altered the distal intestinal microbiota resulting in higher microbial richness and diversity. The diet effect, however, depended on the sample origin. Digesta-associated intestinal microbiota showed more pronounced changes than the mucosa-associated microbiota. Multivariate association analyses identified two mucosa-enriched taxa, Brevinema andersonii and Spirochaetaceae, associated with the expression of genes related to immune responses and barrier function in the distal intestine, respectively. Conclusions: Our data show that salmon intestinal digesta and mucosa harbor microbial communities with clear differences. While feeding insects increased microbial richness and diversity in both digesta- and mucosa-associated intestinal microbiota, mucosa-associated intestinal microbiota seems more resilient to variations in the diet composition. To fully unveil the response of intestinal microbiota to dietary changes, concurrent profiling of digesta- and mucosa-associated intestinal microbiota is recommended whenever feasible. Specific taxa enriched in the intestinal mucosa are associated to gene expression related to immune responses and barrier function. Detailed studies are needed on the ecological and functional significance of taxa associated to intestinal microbiota dwelling on the mucosa. [ABSTRACT FROM AUTHOR]

Functional feed ingredients are frequently used in feeds for Atlantic salmon, often claimed to improve immune functions in the intestine and reduce severity of gut inflammation. However, documentation of such effects is, in most cases, only indicative. In the present study effects of two packages of functional feed ingredients commonly used in salmon production, were evaluated employing two inflammation models. One model employed soybean meal (SBM) as inducer of a severe inflammation, the other a mixture of corn gluten and pea meal (CoPea) inducing mild inflammation. The first model was used to evaluate effects of two packages of functional ingredients: P1 containing butyrate and arginine, and P2 containing β-glucan, butyrate, and nucleotides. In the second model only the P2 package was tested. A high marine diet was included in the study as a control (Contr). The six diets were fed to salmon (average weight of 177g) in saltwater tanks (57 fish per tank), in triplicate, for 69 days (754 ddg). Feed intake was recorded. The growth rate of the fish was high, highest for the Contr (TGC: 3.9), lowest for SBM fed fish (TGC: 3.4). Fish fed the SBM diet showed severe symptoms of inflammation in the distal intestine as indicated by histological, biochemical, molecular, and physiological biomarkers. The number of differently expressed genes (DEG) between the SBM and Contr fed fish was 849 and comprised genes indicating alteration in immune functions, cellular and oxidative stress, and nutrient digestion, and transport functions. Neither P1 nor P2 altered the histological and functional symptoms of inflammation in the SBM fed fish importantly. Inclusion of P1 altered expression of 81 genes, inclusion of P2 altered 121 genes. Fish fed the CoPea diet showed minor signs of inflammation. Supplementation with P2 did not change these signs. Regarding composition of the microbiota in digesta from the distal intestine, clear differences regarding beta-diversity and taxonomy between Contr, SBM, and CoPea fed fish were observed. In the mucosa the microbiota differences were less clear. The two packages of functional ingredients altered microbiota composition of fish fed the SBM and the CoPea diet towards that of fish fed the Contr diet. • Diets: control, two inflammation diets and two mixes of functional ingredients. • Functional ingredients did not improve histological inflammation markers. • Functional ingredients modulated some molecular immune and stress markers. • Functional ingredients altered microbiota towards that in fish fed the control diet. [ABSTRACT FROM AUTHOR]

Background: The present study was undertaken to gain knowledge on the role of bile components and lecithin on development of aberrations in digestive functions which seemingly have increased in Atlantic salmon in parallel with the increased use of plant ingredients in fish feed. Post smolt Atlantic salmon were fed for 77 days one of three basal diets: a high fish meal diet (HFM), a low fishmeal diet (LFM), or a diet with high protein soybean meal (HPS). Five additional diets were made from the LFM diet by supplementing with: purified taurocholate (1.8 %), bovine bile salt (1.8 %), taurine (0.4 %), lecithin (1.5 %), or a mix of supplements (suppl mix) containing taurocholate (1.8 %), cholesterol (1.5 %) and lecithin (0.4 %). Two additional diets were made from the HPS diet by supplementing with: bovine bile salt (1.8 %) or the suppl mix. Body and intestinal weights were recorded, and blood, bile, intestinal tissues and digesta were sampled for evaluation of growth, nutrient metabolism and intestinal structure and function. Results: In comparison with fish fed the HFM diet fish fed the LFM and HPS diets grew less and showed reduced plasma bile salt and cholesterol levels. Histological examination of the distal intestine showed signs of enteritis in both LFM and HPS diet groups, though more pronounced in the HPS diet group. The HPS diet reduced digesta dry matter and capacity of leucine amino peptidase in the distal intestine. None of the dietary supplements improved endpoints regarding fish performance, gut function or inflammation in the distal intestine. Some endpoints rather indicated negative effects. Conclusions: Dietary supplementation with bile components or lecithin in general did not improve endpoints regarding performance or gut health in Atlantic salmon, in clear contrast to what has been previously reported for rainbow trout. Follow-up studies are needed to clarify if lower levels of bile salts and cholesterol may give different and beneficial effects, or if other supplements, and other combinations of supplements might prevent or ameliorate inflammation in the distal intestine. [ABSTRACT FROM AUTHOR]

Symptoms indicating digestive malfunction have been observed in cultivated salmon over the last 10–15 years, at least partially as a consequence of use of new feed ingredients. The present knowledge on many aspects of digestive functions in fish is limited, in particular for Atlantic salmon. Strengthening is needed to understand the mechanisms underlying challenges to gastrointestinal health and to find means to prevent their development. The present paper supplies information regarding digestive enzyme optima and stability, chyme pH and enzyme activities along the digestive tract of Atlantic salmon. The data presented includes new data from four studies on Atlantic salmon as well as a review of comparative literature from various other fish studies. The four experiments comprised salmon of different sizes, kept in salt or fresh water, and fed high fish meal diets with different protein to energy ratios (P/E). These studies showed an average pH in the stomach chyme, i.e. across diets and experiments, of 4.8 (SD = 0.7), whereas the observed pH optimum for pepsin was 3.0. In the intestinal chyme, pH increased throughout the intestine from a mean of 8.1 (SD = 0.23) in the proximal intestine to 8.4 in the mid intestine (SD = 0.27) and distal intestine (SD = 0.29). Total proteolytic activity of chyme in the proximal intestine, measured as the sum of the work of all proteolytic enzymes on casein as substrate, showed its maximum at pH 8.8, i.e. clearly above prevailing chyme pH. For the individual proteolytic enzymes, pH optimum varied from 7.10 for elastase 1 to 8.98 for trypsin. Chyme pH did not appear to be influenced by fish size, but was significantly higher in the fish raised in fresh water than in those raised in salt water. In the intestinal chyme pH showed a significant negative regression on diet P/E. For the investigated pancreatic enzymes in the intestinal chyme, the activity in the chyme decreased from proximal to distal regions and faecal activities were very low compared to the activities in the proximal intestine. The activity profile for leucine aminopeptidase (LAP), however, trended to increase from mid to distal intestine. Chyme enzyme activities along the intestinal tract did not differ clearly between the experiments and no clear relationship between P/E on enzyme activities along the intestinal tract was observed. Remarkable in vitro stability was observed for the proteolytic enzyme activities. [ABSTRACT FROM AUTHOR]

Plants now supply more than 50 % of protein in Norwegian salmon aquafeeds. The inclusion of plant protein in aquafeeds may be associated with decreased lipid digestibility and cholesterol and bile salt levels, indicating that the replacement of fishmeal with plant protein could result in inadequate supplies of cholesterol in fish. A reduction in feed efficiency, fish growth and pathogen resistance is often observed in parallel to alterations in sterol metabolism. Previous studies have indicated that the negative effects induced by plant components can be attenuated when diets are supplemented with cholesterol. The present study evaluated the effects of dietary cholesterol supplementation (1·5 %) in Atlantic salmon fed a plant-based diet for 77 d. The weights of body, intestines and liver were recorded and blood, tissues, faeces, chyme and bile were sampled for the evaluation of effects on growth, nutrient utilisation and metabolism, and transcriptome and metabolite levels, with particular emphasis on sterol metabolism and organ structure and function. Cholesterol supplementation did not affect the growth or organ weights of Atlantic salmon, but seemed to promote the induction of cholesterol and plant sterol efflux in the intestine while suppressing sterol uptake. Cholesterol biosynthesis decreased correspondingly and conversion into bile acids increased. The marked effect of cholesterol supplementation on bile acid synthesis suggests that dietary cholesterol can be used to increase bile acid synthesis in fish. The present study clearly demonstrated how Atlantic salmon adjusted their metabolic functions in response to the dietary load of cholesterol. It has also expanded our understanding of sterol metabolism and turnover, adding to the existing, rather sparse, knowledge of these processes in fish. [ABSTRACT FROM PUBLISHER]

Genetically modified (GM) plants were first grown commercially more than 20 years ago, but their use is still controversial in some parts of the world. Many GM plant varieties are produced in large quantities globally and are approved for use in fish feeds both in Norway and the European Union. European consumers, however, are skeptical to fish produced by means of GM feed ingredients. Concerns have been raised regarding the safety of GM plants, including potential toxicity and (or) allergenicity of the novel protein, potential unintended effects, and risk of horizontal gene transfer to other species. This review will present the current state of knowledge regarding GM plants as fish feed ingredients, focusing on fish performance and health as well as the fate of the GM DNA fragments in the fish, identifying limitations of the current work and areas where further research is needed. Les plantes génétiquement modifiées (GM) ont commencé à être cultivées commercialement il y a plus de 20 ans, mais leur utilisation reste controversée dans certaines régions du globe. Plusieurs variétés de plantes GM sont produites en grande quantité à l'échelle mondiale et sont acceptées dans la préparation de la nourriture de poissons, tant en Norvège que dans l'Union européenne. Les consommateurs européens maintiennent cependant une certaine inquiétude concernant les poissons produits par l'usage d'ingrédients alimentaires GM. On a manifesté des préoccupations en ce qui a trait à l'innocuité des plantes GM, en particulier à la toxicité et (ou) l'allergénicité potentielles des protéines nouvelles, aux effets potentiels imprévus et au risque de transferts horizontaux des gènes aux autres espèces. Notre rétrospective résume l'état actuel des connaissances sur les plantes GM utilisées comme ingrédients dans l'alimentation des poissons, avec une emphase particulière sur la performance et la santé des poissons, ainsi que sur le sort des fragments d'ADN GM chez les poissons, tout en soulignant les limites des travaux actuels et en identifiant les domaines de recherche additionnelle nécessaire. [ABSTRACT FROM AUTHOR]

In the present study, we aimed to assess the effect of dietary insect meal (IM) and insect oil (IO) on growth performance, body composition and nutrient digestibility of freshwater reared Atlantic salmon. The IM and IO were produced from black soldier fly larvae ( Hermetia illucens , L.; BSF) that had been grown on (1) media containing organic waste streams, or on (2) media partially containing seaweed ( Ascophyllum nodosum ). The feeding trial of the current study followed a factorial 2 × 3 way-ANOVA experimental design with six dietary groups of Atlantic salmon fed diets with insect-derived ingredients for 8 weeks. A typical industrial diet, with protein from fish meal and soy protein concentrate (SPC) (50:50) and lipids from fish oil and vegetable oil (33:66), was fed to a positive control group. Five experimental diets were formulated, where 85% of the dietary protein was replaced by IM and/or all the vegetable oil was replaced by IO (IM from insects grown on media 1, IO from insects grown on either media 1 (IO1) or media 2 (IO2)). Replacing the dietary fish meal and SPC with insect protein significantly reduced the apparent digestibility coefficients (ADC) of protein, lipid and all amino acids investigated, though remained highly digestible. There were, however, only small differences due to protein or lipid source in growth performance, and no effects of insect ingredients on feed intake or feed conversion ratio. Inclusion of IM-based diets significantly increased both hepatosomatic index and visceral somatic index of Atlantic salmon. Proteinase activity in the intestine was not affected by dietary inclusion of BSF larvae meal, while leucine aminopeptidase activity was lower in fish fed with insect ingredients than the control group. Whole-body protein, lipid, amino acids and minerals contents were not affected by protein or lipid source. In general, this study showed that protein meal and oil from BSF larvae hold a great potential as a source of nutrients for Atlantic salmon. [ABSTRACT FROM AUTHOR]

The goal of the present study was to find whether higher soybean meal (SBM) levels might trigger soybean meal-induced enteritis (SBMIE) in turbot. If so, caution must be taken when mixing ingredients containing saponins and other antinutrients to avoid SBMIE like symptoms. In a 8 week feeding trial conduced on turbot, three isonitrogenous and isolipidic diets were formulated to include 26%, 40% and 54% SBM to progressively replace 30%, 45% and 60% fish meal (FM) in a FM based diet, respectively. The results showed that SBM caused dose-dependent decreases in growth performance and nutrient utilization. Enteritis developed in the distal intestine in the inclusion range of 26–54%. Dose-dependent increases in severity of the inflammation, with concomitant alterations in brush border membrane enzymes and inflammatory marker genes expression were seen. Our results confirm the hypothesis that high inclusion level of SBM may cause similar inflammatory changes as observed in several other fish species. Thus, caution must be taken when formulating turbot diets based on ingredients that may contain saponins and other antinutrients. Moreover, turbot is also a candidate species for the study of causes and mechanism of diet induced inflammation in the intestine of fish. Statement of relevance The present work first describes the soybean meal induced enteritis in turbot and provides the information that caution must be taken when formulating turbot diets based on ingredients that may contain saponins of other antinutrients. [ABSTRACT FROM AUTHOR]

The present study aimed to evaluate the effects of two purified antinutrients, soy saponins and phytosterols, in an important species for Mediterranean aquaculture. For this purpose, gilthead seabream ( Sparus aurata ) were fed six experimental diets containing two levels of those antinutrients, alone or in combination, and a control diet, to apparent visual satiation under controlled conditions. Blood and head-kidney were collected at 7, 15 and 48 days following first feeding in order to assess immune parameters and the expression of immune-related genes. Plasma bactericidal and alternative complement pathway activities increased in fish fed antinutrients compared to fish fed the control diet during the course of the experiment, with more important changes at 7 and 48 days for bactericidal activity and at 7 and 15 days for complement values. In contrast, plasma total immunoglobulins (Ig) increased in fish fed antinutrients only at 48 days. Caspase 1 ( casp1 ), interleukin 18 ( il18 ), colony-stimulating factor-1 receptor ( csfr ) and hepcidin ( hep ) presented similar patterns of expression with more important changes at 7 and 48 days, while interleukin 10 ( il10 ) and β-defensin ( def ) were mainly up-regulated in fish fed antinutrients at 48 days. The level of expression of IgM increased already at 7 days in fish fed the low concentration of both saponins and phytosterols while a general up-regulation was observed at 48 days compared to fish fed the control diet. Results suggest that feeding seabream a diet with purified saponins and phytosterols, alone or in combination, induces a number of changes that are related to the development of inflammation, with most important changes in fish fed the lower phytosterols concentration. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the study was to investigate how the replacement of LT-fish meal by a 3.5:1 mixture of an experimentally produced partially deshelled krill meal (PDKM) and a pea protein concentrate (PPC) affected growth rate, digestibility of main nutrients and minerals, fluoride accumulation and histology in Atlantic salmon (Salmo salar). Five extruded diets were fed to salmon with an average weight of 546g, distributed into 15 tanks equipped with flow through sea water. During extrusion, increased krill meal resulted in increased lipid content in the feed mash and subsequently decreased pellet expansion and decreased pellet water stability. The salmon had an optimum growth rate with a PDKM/PPC inclusion of 400gkg−1. Starch digestibility decreased and lipid digestibility increased with increasing PDKM/PPC inclusion. Fluoride in faeces increased linearly with increasing dietary fluoride levels. Plasma cholesterol decreased with increased PDKM/PPC inclusion, whereas no major differences were seen for triglycerides, free fatty acids, glucose, or bile acids. Fish fed increased dietary PDKM/PPC showed an increased prevalence of mild to moderate nephrosis. [Copyright &y& Elsevier]

Abstract: Atlantic cod with an average initial weight of 413 g were fed for 112 days diets containing either 11.4 or 30.5% lipid (of dry matter) until they reached a final weight of approximately 750 g. Samples of intestine, liver and blood were taken at the end of the feeding period, and then after 3 weeks of fasting. The lipid level in the diet did not significantly affect fish growth. The hepatosomatic index (HSI), however, increased by a factor of 1.5, and the liver lipid index by a factor of 1.7, when fish were fed the high-fat diet. The increase in HSI was primarily due to a larger average size of liver cells, due to a higher level of lipid deposition than in the livers of fish fed the low-fat diet, which had more and smaller liver cells with less lipid. Vesicles with the size of very low density lipoproteins (VLDLs) were found in liver cells of fish fed the high-fat diet. In fish from the same dietary group, vesicles with the size of chylomicrons were found in intestinal enterocytes. These particles were however not present in tissues from fasted fish. The cholesterol and protein rich high density lipoprotein (HDL) was the predominant lipoprotein class in cod serum, with the triacylglycerol (TAG) rich low density lipoprotein (LDL) as the next most common class. Some TAG-rich VLDLs and chylomicrons were also present in the serum. The apo-lipoprotein compositions of the lipoprotein classes in cod were similar to those of other species: the apoB was the major protein in chylomicrons, VLDLs and LDLs, while apoA predominated in HDLs. There was a tendency to reduced liver lipid index in fasted fish, indicating lipid mobilisation from the liver. The fatty acid (FA) serum profile showed an increased percentage of saturated FAs, while there was a reduction in the percentage of saturated FAs in the liver with fasting, indicating a higher mobilisation of saturated FAs relative to other FAs. The increased degree of blood capillary vascularisation (angiogenesis) found after fasting is likely to improve the supply of nutrients and FAs from the liver via serum to other organs and tissues. Mobilised lipids were mainly transported esterified in TAG, primarily in HDL, less in LDL. [Copyright &y& Elsevier]