Kan fisk vokse på trær? Næringsverdi og funksjonelle egenskaper av gjær i fôret til Atlantisk laks (Salmo salar)

Yeasts are gaining attention as alternative ingredients in fish feeds. The nutritional and health potentials of non-saccharomyces yeasts in fish are scarce in literature. Three non-saccharomyces yeasts; Cyberlindnera jadinii (CJ), Blastobotrys adeninivorans (BA) and Wickerhamomyces anomalus (WA) are the focus of this thesis. The objective of the current thesis was to investigate the nutritional values and health effects of the three selected yeasts in the diets of Atlantic salmon (Salmo salar) with focus on growth performance, intestinal health, gut microbiota, and immune responses of fish. The three yeasts were produced in-house using a growth medium containing a blend of enzymatic hydrolysates of pre-treated spruce wood (Picea abies) and chicken by-products. After harvesting, the selected yeasts were processed by direct heat-inactivation with spray-drying (ICJ, IBA and IWA) or autolyzed at 50 ºC for 16 h, followed by spray-drying (ACJ, ABA and AWA). The present thesis comprises of seven papers. Paper I used a desk study approach to review the state-of-the art on the use of yeasts in fish feeds and identified gaps in literature regarding the use of yeasts as aquafeed ingredients. Yeasts are efficient converter of low-value non-food biomass into high-value resources. Yeasts showed comparatively similar amino acids with fishmeal (FM) and soybean meal (SBM), except for methionine, lysine, arginine, and phenylalanine which need to be supplemented when used in fish feeds. Genetic modification and/or nutrient digestibility through exogenous enzyme supplementation and the use of cost-effective down-stream processing (DSP) are possible strategies to increase the nutritive values of yeasts in fish. Additional investment in large-scale production at competitive price is needed for yeasts to be considered as feasible replacement for FM and SBM in fish feeds. Paper II investigated the impacts of yeast species and processing on performance, immune response and gut health of Atlantic salmon fry fed SBM-based diet in freshwater. In a 37-day feeding experiment, the fish were fed one of the nine experimental diets: a FM-based diet, a challenging diet with 40% SBM and six other diets containing 40% SBM and 5% each of ICJ, ACJ, IBA, ABA, IWA and AWA yeast products. An additional control containing 40% SBM and 5% of a reference inactivated C. jadinii (ICU), known for its ability to counteract SBM-induced enteritis (SBMIE) was used in this experiment. C. jadinii and W. anomalus yeasts showed the most promising effects on gut health based on widening of lamina propria and immune response parameters. The AWA was effective in ameliorating SBMIE in fish, while only limited effects were observed for other yeasts products. The ability of yeasts to counteract SBMIE is linked to the activation of immune responses in fish. The results also revealed that the amounts, length, adhesion, and accessibility of cell wall components could be important for the ameliorating effects of yeasts on SBMIE in fish. Paper III assessed the effects of yeasts species and processing on systemic immune response of Atlantic salmon fry fed SBM-based diet in freshwater and demonstrated whether spleen can be used as a target organ to characterize immunomodulatory effects of functional ingredients in fish. The production of yeasts, experiment diets and fish experimental protocol were fully described in Paper II. Four experimental diets (FM, SBM, ICJ, and ACJ) were used in Paper III. The immunomodulatory effects of the diets were analyzed in the spleen of fish after 37 days of feeding, using a transcriptomic evaluation by RNA sequencing and protein expression of specific immunological markers through indirect ELISA. The results showed that SBM induced a down-regulation of pathways associated with ion binding and transport, along with an increase at the protein levels of pro-inflammatory cytokines TNFα and IFNγ. The inclusion of ACJ in the diet was able to control the inflammatory profile caused by SBM through activation of biological pathways related to endocytosis, along with increased protein expression of IL-10 and decreased level of TNFα. The functionality of yeasts in improving gut health of fish is dependent on the yeast species and DSP used after harvesting the yeasts. The results also showed that spleen was a good target organ to characterize the immunomodulatory effects of functional ingredients in Atlantic salmon. Paper IV investigated the effects of yeast species and processing on nutrient digestibility of yeasts in Atlantic salmon. The production and processing of yeasts used in Paper IV were as described in Paper II. Seven experimental diets were used in paper. The control feeds consisted of 100% reference diet (REF) and six other diets comprising of 70% REF diet and 30% each of the yeast products (ICJ, ACJ, IBA, ABA, IWA and AWA). The protein and amino acids of the three yeast species were moderately digested in Atlantic salmon. Autolysis slightly increased protein digestibility of C. jadinii and W. anomalus in Atlantic salmon, but not B. adeninivorans. The results revealed that cell wall porosity as demonstrated by nitrogen solubility had larger impact on nutrient digestibility of yeasts than cell wall thickness. The nutrient digestibility of yeasts in Atlantic salmon is dependent on the yeast species and DSP used after harvesting the yeasts. Based on the results of Papers II, III and IV, a second batch of C. jadinii and W. anomalus yeast were produced to understand the response of Atlantic salmon reared in seawater to dietary yeasts. Therefore, Paper V evaluated the effects of yeasts species and processing on intestinal health and transcriptomic profile from DI and spleen tissue of Atlantic salmon fed SBM-based diet in seawater. The yeasts were produced and processed following the procedure described in Paper II. The ICJ, ACJ, IWA and AWA yeasts products were used in this paper. Six diets were formulated, one based on FM, a challenging diet containing 30% SBM and four other diets containing 30% SBM and 10% each of the yeast products (ICJ, ACJ, IWA and AWA). The inclusion of ICJ and ACJ yeasts reduced the loss of enterocyte supranuclear vacuolization and reduced the population of CD8α positive cells in the lamina propria of fish fed SBM diets. The ICJ and ACJ yeasts controlled the inflammatory profile through upregulation of pathways connected to wound healing and taurine metabolism. The IWA and AWA yeasts controlled the inflammatory profile in fish fed SBM through down-regulation of pathways associated with toll-like receptor signaling, C-lectin receptor and signal transduction. This paper strengthened our earlier observations (Papers II and III) that C. jadinii and W. anomalus are promising novel ingredients with health beneficial effects in terms of controlling distal intestine inflammation associated by feeding plant based diets to Atlantic salmon. Paper VI investigated the effects of yeast species and processing on gut microbiota of fish. The yeast production and processing, experimental diets and fish experimental protocol were as described in Paper V. After 42 days of feeding, six fish from each tank were randomly selected to collect digesta samples from the DI for 16S rRNA sequencing. Water samples (from the source and rearing tanks) and feed samples were also collected for the sequencing analysis. The microbiota of fish fed SBM diet differed from those fed FM diet. The microbiota composition, richness and diversity were similar in fish fed ICJ, IWA and SBM diets. Fish fed ACJ increased relative abundance of Pediococcus, and mucin O-glycan degradation pathway, while fish fed AWA diet increased relative abundance of Bacillaceae compared with fish fed the other diets. Despite the significant modulation of intestinal microbiota of fish fed the autolyzed yeasts (ACJ and AWA), the histological and transcriptomic results revealed that the autolyzed yeasts did not improve gut health of fish beyond the level observed for the inactivated yeasts (ICJ and IWA) (Paper V). These results suggest that the ameliorating effects of yeasts on SBMIE is connected to their ability to stimulate immune responses in Atlantic salmon (Papers II, III and V), rather than through modulation of intestinal microbiota (Paper VI).publishedVersio

Fish, roots, tubers and bananas: opportunities and constraints for agri-food system integration

Agri-food system integration has the potential to increase and add value to agricultural production, reduce cost of and dependency on external inputs, generate additional income to farmers, and encourage the diversification of outputs and diets. Agri-food system integrations such as livestock-fish, poultry-fish, crop-livestock and rice-fish farming have been well documented in academic literature. However, information on fish and root, tuber and banana (RTB) crops integration is scarcely available, despite their worldwide cultural, dietary, and economic importance. This article, which is informed by a narrative literature review and ground-truthing through key informant interviews, documents existing linkages between two agri-food systems – fish and RTB – and identifies opportunities and challenges for strengthening their integration. We found that recorded instances of fish-RTB integration are limited and predominantly discuss production-related activities. Nevertheless, initial evidence suggests that there are important livelihood-enhancing opportunities as well as environmental, nutrition and food-security related benefits, which need to be considered. These include the potential to improve the nutritional status of vulnerable populations and lower the cost of fish production and thus improve the livelihoods of small-scale fish farmers. Further field-based research is recommended to explore these outcomes in more detail

A meta-analysis to determine factors associated with the severity of enteritis in Atlantic salmon (Salmo salar) fed soybean meal-based diets

A meta-analytic approach was used to determine factors associated with the severity of enteritis in distal intestine of Atlantic salmon fed soybean meal (SBM)-based diets. Dataset from 26 fish studies were extracted and standardized for use in the meta-analysis. After standardization, the data were analyzed with ordinal logistic regression model by comparing the SBM treatment(s) in each study with the neutral-reference treatment. The log-odds ratio of the proportional odds model and its standard error were extracted and analyzed using the random effects model to estimate the effect size of dietary SBM on enteritis using four semi-quantitative histological variables: reduction in mucosal fold height; disappearance of supranuclear vacuolization; inflammatory cell infiltration of lamina propria, and of submucosa. Both univariate and multivariate meta-regression were used to identify study factors with significant association to the severity of enteritis in Atlantic salmon. The results showed that fish production phase, feed type, SBM inclusion level, year of study and water temperature are significantly associated with the severity of enteritis in Atlantic salmon. Further meta-analysis of sub datasets according to production phase, revealed that fish reared in seawater were more prone to develop enteritis compared with fish reared in freshwater. The absence of positive relationship between SBM inclusion level and the severity of enteritis was probably due to difference in source, batch, processing, and level of anti-nutritional factors in the SBM used in the different studies combined in the meta-analysis. Subgroup analysis based on year of study revealed that the severity of enteritis in fish fed SBM-based diets has decreased over the years. Additional results revealed that fish fed SBM-based diet at low water temperature showed increased severity of enteritis, compared with fish raised in high water temperature. Linear and quadratic regressions conducted to explore possible impact of enteritis on fish performance, showed that the specific growth rate and thermal growth coefficient of fish decreased with increased severity of enteritis. However, this relationship depends on the fish production phase and the histological variables used for the regression analysis. The current study concluded that the severity of enteritis in Atlantic salmon fed SBM-based diets are significantly associated with fish production phase, feed type, SBM inclusion level, year of study and water temperature, but not the exposure time. Also, the study showed that increased severity of enteritis reduced specific growth rate and thermal growth coefficient of fish fed SBM-based diets.A meta-analysis to determine factors associated with the severity of enteritis in Atlantic salmon (Salmo salar) fed soybean meal-based dietspublishedVersio

Effects of Yeast Species and Processing on Intestinal Health and Transcriptomic Profiles of Atlantic Salmon (Salmo salar) Fed Soybean Meal-Based Diets in Seawater

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Yeast as major protein-rich ingredient in aquafeeds: a review of the implications for aquaculture production

Sustainability concerns associated with protein sources and currently used fishmeal and plant-based meal have necessitated the quests for novel sustainable ingredients for use in aquafeeds. Yeasts have been proposed as sustainable ingredients particularly because of their potential to valorise non-food lignocellulosic biomass into valuable protein resources. Prior to now, extensive studies exist on the role of yeast cell wall components in modulating health responses of fish. However, research on its use as a major protein source in fish diets is still in its infancy. The current review collates, synthesises and discusses the prospects of five major yeast species as future protein ingredients with respect to their nutritional adequacy in fish. Nutritional quality of Saccharomyces cerevisiae, Cyberlindnera jadinii, Kluyveromyces marxianus, Blastobotrys adeninivorans and Wickerhamomyces anomalus and their use as replacement for fishmeal and soy protein in the diets of Atlantic salmon and rainbow trout are discussed based on three protein quality indices: chemical score, essential amino acid index and ideal protein concept based on the first limiting amino acids, methionine. The crude protein contents of yeast (40–55%) are lower than that of fishmeal, but comparable with soya bean meal. Compared to fishmeal, the different yeast species have favourable amino acid profiles, except for methionine, lysine, arginine and phenylalanine which are the frequently limiting essential amino acids in Atlantic salmon and rainbow trout. This review also presents future area of research and emphasise the need for large-scale production of yeast at competitive price to constitute a feasible replacement for fishmeal and soy protein in aquaculture.publishedVersio

Yeast as major protein-rich ingredient in aquafeeds: a review of the implications for aquaculture production

Sustainability concerns associated with protein sources and currently used fishmeal and plant-based meal have necessitated the quests for novel sustainable ingredients for use in aquafeeds. Yeasts have been proposed as sustainable ingredients particularly because of their potential to valorise non-food lignocellulosic biomass into valuable protein resources. Prior to now, extensive studies exist on the role of yeast cell wall components in modulating health responses of fish. However, research on its use as a major protein source in fish diets is still in its infancy. The current review collates, synthesises and discusses the prospects of five major yeast species as future protein ingredients with respect to their nutritional adequacy in fish. Nutritional quality of Saccharomyces cerevisiae, Cyberlindnera jadinii, Kluyveromyces marxianus, Blastobotrys adeninivorans and Wickerhamomyces anomalus and their use as replacement for fishmeal and soy protein in the diets of Atlantic salmon and rainbow trout are discussed based on three protein quality indices: chemical score, essential amino acid index and ideal protein concept based on the first limiting amino acids, methionine. The crude protein contents of yeast (40–55%) are lower than that of fishmeal, but comparable with soya bean meal. Compared to fishmeal, the different yeast species have favourable amino acid profiles, except for methionine, lysine, arginine and phenylalanine which are the frequently limiting essential amino acids in Atlantic salmon and rainbow trout. This review also presents future area of research and emphasise the need for large-scale production of yeast at competitive price to constitute a feasible replacement for fishmeal and soy protein in aquaculture

Yeast as a novel protein source - Effect of species and autolysis on protein and amino acid digestibility in Atlantic salmon (Salmo salar)

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Nutritive values of wheat bran-based broiler diet supplemented with different classes of enzymes

Previous studies have shown that inclusion of exogenous enzymes in broiler diets can improve metabolizable energy intakes, digestibility and performance parameters. However, there is limited information on the comparative effect of different enzymes in wheat bran-based broiler diet. This study investigated the effect of different enzyme classes on metabolizable energy (ME) values of wheat bran as well as the performance parameters and nutrient retention of broilers. A total of 216 mixed-sex one-day-old chicks were fed either the basal diet or test diet (20% basal diet replaced with wheat bran) without or with supplementation of carbohydrase-cocktail (CC), multi-enzyme (MEnz) and single-carbohydrase (SC). The enzymes increased (P<0.001) the ME values of wheat bran but SC had the highest increase for apparent ME, nitrogen-corrected apparent ME and true ME values of wheat bran. Neither performance parameters of feed intake (FI), body weight gain (BWG), feed conversion ratio (FCR) nor economic benefit (EB) was affected by the interaction between diets and enzymes. A significant dietary effect (P<0.05) was observed as higher FI, lower FCR, and better EB on the test diet compared to basal diet. The enzyme inclusions, however, had similar improvements on (P<0.05) on BWG, FCR and EB of broilers. The dietary enzymes increased fat and phosphorus (P) retentions on both test and basal diets (P<0.001), with birds fed CC added to test diet showing the highest phosphorus retention. In conclusion, enzyme inclusions in wheat-bran based diet improved the ME values of wheat bran and the nutrient retention of broilers, although broiler performance was unaffected. The inclusion of CC in 20% wheat bran-based diet can be economically useful in improving P retention of broilers, with potential benefit for reducing P losses to the environment.</p

The Spleen as a Target to Characterize Immunomodulatory Effects of Down-Stream Processed Cyberlindnera jadinii Yeasts in Atlantic Salmon Exposed to a Dietary Soybean Meal Challenge

publishedVersio

A meta-analysis to determine factors associated with the severity of enteritis in Atlantic salmon (Salmo salar) fed soybean meal-based diets

A meta-analytic approach was used to determine factors associated with the severity of enteritis in distal intestine of Atlantic salmon fed soybean meal (SBM)-based diets. Dataset from 26 fish studies were extracted and standardized for use in the meta-analysis. After standardization, the data were analyzed with ordinal logistic regression model by comparing the SBM treatment(s) in each study with the neutral-reference treatment. The log-odds ratio of the proportional odds model and its standard error were extracted and analyzed using the random effects model to estimate the effect size of dietary SBM on enteritis using four semi-quantitative histological variables: reduction in mucosal fold height; disappearance of supranuclear vacuolization; inflammatory cell infiltration of lamina propria, and of submucosa. Both univariate and multivariate meta-regression were used to identify study factors with significant association to the severity of enteritis in Atlantic salmon. The results showed that fish production phase, feed type, SBM inclusion level, year of study and water temperature are significantly associated with the severity of enteritis in Atlantic salmon. Further meta-analysis of sub datasets according to production phase, revealed that fish reared in seawater were more prone to develop enteritis compared with fish reared in freshwater. The absence of positive relationship between SBM inclusion level and the severity of enteritis was probably due to difference in source, batch, processing, and level of anti-nutritional factors in the SBM used in the different studies combined in the meta-analysis. Subgroup analysis based on year of study revealed that the severity of enteritis in fish fed SBM-based diets has decreased over the years. Additional results revealed that fish fed SBM-based diet at low water temperature showed increased severity of enteritis, compared with fish raised in high water temperature. Linear and quadratic regressions conducted to explore possible impact of enteritis on fish performance, showed that the specific growth rate and thermal growth coefficient of fish decreased with increased severity of enteritis. However, this relationship depends on the fish production phase and the histological variables used for the regression analysis. The current study concluded that the severity of enteritis in Atlantic salmon fed SBM-based diets are significantly associated with fish production phase, feed type, SBM inclusion level, year of study and water temperature, but not the exposure time. Also, the study showed that increased severity of enteritis reduced specific growth rate and thermal growth coefficient of fish fed SBM-based diets