A. Makol

Reduced gut bacterial translocation in European sea bass (Dicentrarchus labrax) fed mannan oligosaccharides (MOS)

The objective of this study was to determine the effect of mannan oligosaccharides derived from the outer cell wall of a select strain of Saccharomyces cerevisiae (Bio-Mos, Alltech Inc, USA) on mucus production, selected mucus immune parameters activity, gut morphology and in vivo and ex vivo gut bacterial translocation for European sea bass (Dicentrarchus labrax). Specimens were fed 4 g kg⁻¹ dietary MOS level of inclusion in a commercial sea bass diet for eight weeks. At the end of this period, anterior gut mucosal folds height, width and folds surface area were increased by MOS supplementation (P < 0.05, n = 240). Posterior gut presented shorter folds (P < 0.05, n = 240) but wider that those fed control diet (P < 0.05, n = 240) resulting in increased total surface area (P < 0.05, n = 240). For rectum, feeding MOS reduced fold length (P < 0.05, n = 240). Gut morphological analyses showed an enhancement in the number of cells secreting acid mucins by area unit, higher density of eosinophilic granulocytes (ECGs) in the mucosa for fish fed MOS together with an improvement in gut mucus lysozyme activity which could be related to the reduced in vivo and ex vivo gut bacterial translocation found. No differences were found for the skin mucus immune parameters evaluated.

Enhanced intestinal epithelial barrier health status on European sea bass (Dicentrarchus labrax) fed mannan oligosaccharides.

The study assesses the effects of dietary mannan oligosaccharides (MOS) in European sea bass (Dicentrarchus labrax) posterior intestinal lipid class composition and its possible relation to the potential prostaglandins production and Gut Associated Lymphoid Tissue (GALT) stimulation. Fish were fed 4 g kg(-1) MOS (Bio-Mos(®) Aquagrade, Alltech, Inc., USA) for eight weeks. Fish fed MOS presented higher (P ≤ 0.05) weight gain, total length, and specific and relative growth rates than fish fed the control diet. Stimulated posterior gut of fish fed MOS showed higher (P ≤ 0.05) prostaglandins production than fish fed the control diet. Lipid class analyses of posterior gut revealed a reduction (P ≤ 0.05) in the neutral lipid fraction in fish fed MOS compared to fish fed the control diet, particularly due to a reduction (P ≤ 0.05) in triacylglycerols content. The polar lipid fraction increased (P ≤ 0.05) in fish fed MOS compared to fish fed the control diet, mainly due to an increase (P ≤ 0.05) in phosphatidylethanolamine and phosphatidylcoline contents. Light microscopy of posterior gut revealed increased number or goblet cells as well as higher level of infiltrated eosinophilic granulocytes for fish fed MOS. Transmission electron microscopy qualitative observations revealed a better preserved cytoarchitecture of the intestinal epithelial barrier in the posterior gut of fish fed MOS. Posterior gut of fish fed MOS presented more densely packed non-damaged enterocytes, better preserved tight junctions structure, healthier and more organized microvilli, and a higher presence of infiltrated lymphocytes and granulocytes compared fish fed the control diet. The present study indicates that dietary MOS enhances European sea bass posterior gut epithelial defense by increasing membrane polar lipids content in relation to a stimulation of the eicosanoid cascade and GALT, promoting posterior gut health status.

Effect of conjugated linoleic acid on dietary lipids utilization, liver morphology and selected immune parameters in sea bass juveniles (Dicentrarchus labrax)

Increased energy content in fish feeds has led to an enhanced fat deposition, particularly in European sea bass, concerning fish farmers. Inclusion of conjugated linoleic acid (CLA) could reduce fat deposition as in other vertebrates. To determine if dietary CLA affects fat deposition, lipid metabolism, lipid composition and morphology of different tissues, growth and selected immune parameters, European sea bass juveniles were fed 4 graded levels of CLA (0, 0.5, 1 and 2%). Growth and feed conversion were not affected by CLA, whereas feed intake was reduced (P<0.05) by feeding 2% CLA. In these fish perivisceral fat was also reduced (P<0.05), particularly reducing (P<0.05) monounsaturated fatty acids. CLA has not affected tissue proximal composition, but reduced (P<0.05) saturated and monounsaturated fatty acids and increased (P<0.05) the n-3 and n-3 highly unsaturated fatty acids in muscle and increase (P<0.05) CLA content in muscle, liver and perivisceral fat. A progressive reduction in lipid vacuolization of hepatocytes cytoplasm and regular-shaped morphology was found in fish fed increased CLA levels, together with a progressive increase in malic enzyme activity (only significant in fish fed 1% CLA). Finally, inclusion of CLA up to 1% increased (P<0.05) plasma lysozyme activity and was positively correlated with alternative complement pathway.

Feeding European sea bass (Dicentrarchus labrax) juveniles with a functional synbiotic additive (mannan oligosaccharides and Pediococcus acidilactici): An effective tool to reduce low fishmeal and fish oil gut health effects?

&NA; The aim of this study was to assess the effects of dietary mannan oligosaccharides (MOS), Pediococcus acidilactici or their conjunction as a synbiotic in low fish meal (FM) and fish oil (FO) based diets on European sea bass (Dicentrarchus labrax) disease resistance and gut health. For that purpose, sea bass juveniles were fed one of 6 diets containing different combinations of MOS (Biomos® and Actigen©; Alltech, Inc., Kentucky, USA) and Pediococcus acidilactici (BAC, Bactocell®; Lallemand Inc., Cardiff, UK) replacing standard carbohydrates as follows (MOS (%)/BAC (commercial recommendation): high prebiotic level (HP) = 0.6/0, low prebiotic level (LP) = 0.3/0, only probiotic (B) = 0/+, high prebiotic level plus probiotic (HPB) = 0.6/+, low prebiotic level plus probiotic (LPB) = 0.3/+, control (C) = 0/0 for 90 days. After 60 and 90 days of feeding trial, fish were subjected to an experimental infection against Vibrio anguillarum. Additionally, inducible nitric oxide synthase (iNOS) and tumor necrosis factor &agr; (TNF&agr;) gut patterns of immunopositivity and major histocompatibility complex class II (MHCII), transforming growth factor &bgr; (TGF‐&bgr;), regulatory T‐cell subset (CD4+T lymphocytes) and effector T cell (CD8&agr;+ T lymphocytes) gene expression patterns in gut by in situ hybridization were evaluated after 90 days of feeding. The effects of both additives on posterior gut through Gut Associated Lymphoid Tissue (GALT) gene expression was also studied. Fish fed the prebiotic and its combination with P. acidilactici presented increased weight regardless of the dose supplemented after 90 days of feeding, however no effect was detected on somatic indexes. For posterior gut, morphometric patterns and goblet cells density was not affected by MOS, P. acidilactici or its combination. Anti‐iNOS and anti‐TNF&agr; gut immunopositivity patterns were mainly influenced by MOS supplementation and not by its combination with P. acidilactici. MHCII‐&bgr;, TCR‐&bgr;, CD4 and CD8‐&agr; positive cells distribution and incidence was not affected by diet. Fish fed HP dose presented a clear up‐regulation of TNF‐&agr;, cyclooxygenase‐2 (COX‐2), CD4 and IL10, whereas P. acidilactici dietary supplementation increased the number of interleukin‐1&bgr; (IL1&bgr;) and COX‐2 gene transcripts. Synbiotic supplementation resulted in a reduction of MOS‐induced gut humoral proinflammatory response by increasing the expression of some cellular‐immune system related genes. Fish mortality after V. anguillarum infection was reduced in fish fed LPB and LP diets compared to fish fed the non‐suppelmented diet after 90 days of feeding. Thus, overall pointing to the combination of a low dose of MOS and P. acidilactici as synbiont (LPB) as a viable tool to potentiate European sea bass juveniles growth and disease resistance when supplemented in low FM and FO diets. HighlightsDietary MOS and its combination with P. acidilactici promotes growth performance.The dietary combination of low prebiotic dose MOS and P. acidilactici increase the density of posterior gut goblet cells.MOS dietary dose is a determining factor in terms of the gut proinflammatory pattern of response.P. acidilactici helps fish to reach gut intestinal homeostasis after fed fish with low FM and FO diets.Dietary MOS and its combination with P. acidilactici increase fish disease resistance against V. anguillarum.