Effects of dietary arabinoxylan-oligosaccharides (AXOS) and endogenous probiotics on the growth performance, non-specific immunity and gut microbiota of juvenile Siberian sturgeon (Acipenser baerii) Zahra Geraylou a, b, * , Caroline Souffreau a , Eugene Rurangwa a, c , Luc De Meester a , Christophe M. Courtin d , Jan A. Delcour d , Johan Buyse b , Frans Ollevier a a Laboratory of Aquatic Ecology, Evolution and Conservation, KU Leuven, Leuven, Belgium b Laboratory of Livestock Physiology, Immunology and Genetics, KU Leuven, Leuven, Belgium c Institute for Marine Resources and Ecosystem Studies (IMARES), Wageningen UR, Yerseke, The Netherlands d Laboratory of Food Chemistry and Biochemistry & Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Leuven, Belgium article info Article history: Received 12 May 2013 Received in revised form 3 June 2013 Accepted 10 June 2013 Available online 25 June 2013 Keywords: Siberian sturgeon AXOS Probiotics Synbiotic Immune responses abstract We investigated the effects of administration of putative endogenous probiotics Lactococcus lactis spp. lactis or Bacillus circulans, alone and in combination with arabinoxylan-oligosaccharides (AXOS), a new class of candidate prebiotics, in juvenile Siberian sturgeon (Acipenser baerii). Eight experimental diets were tested: basal diet (Diet 1), basal diet supplemented with 2% AXOS (Diet 2), or L. lactis ST G81 (Diet 3), L. lactis ST G45 (Diet 4), B. circulans ST M53 (Diet 5), L. lactis ST G81 þ 2% AXOS (Diet 6), L. lactis ST G45 þ 2% AXOS (Diet 7), B. circulans ST M53 þ 2% AXOS (Diet 8). After four weeks, growth performance and feed conversion ratio significantly improved in fish fed diet 7. Innate immune responses of fish were boosted with both AXOS and probiotic diets, however synergistic effects of AXOS and probiotic diets were only observed for phagocytic and alternative complement activity. Phagocytic and respiratory burst activity of fish macrophage increased in fish fed diet 2 and 7, while humoral immune responses only increased in fish fed diet 7. Pyrosequencing analysis (16S rDNA) of the hindgut microbiota demonstrated that AXOS improved the colonization or/and growth capacity of L. lactis, as a higher relative abundance of L. lactis was observed in fish receiving diet 7. However, no observable colonization of B. circulans was found in the hindgut of fish fed diet 5 or 8, containing this bacterium. The dietary L. lactis ST G45 þ 2% AXOS caused significant alterations in the intestinal microbiota by significantly decreasing in bacterial diversity, demonstrated by the fall in richness and Shannon diversity, and improved growth performance and boosted immune responses of Siberian sturgeon. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, sturgeon culture has developed into a very successful industry, due to the precious eggs (caviar) and meat. Intensive culture exposes the fish to different sources of stress such as high stocking densities and manipulations. Development of effective methods to boost the fish immune system and to avoid infectious diseases is therefore vital. Traditional disease control strategies include antibiotics and chemical disinfectants. However, these are no longer recommended practices due to the emergence of bacterial resistance [1] and concerns about environmental impact and wildlife protection [2]. In the past decennium, natural prophylactic supplements including probiotics and prebiotics have received a great deal of attention to replace chemotherapeutics in aquaculture. Probiotics are defined as live microbial feed supple- ments which beneficially affect the host animal by improving its intestinal microbial balance [3]. Several studies have demonstrated that probiotics can improve growth performance, feed utilization, digestibility of dietary ingredients, disease resistance and immune responses of aquatic animals [4e7]. The most common probiotics * Corresponding author. Laboratory of Aquatic Ecology, Evolution and Conser- vation, Zoological institute, KU Leuven, Charles Deberiotstraat 32, 3000 Leuven, Belgium. Tel.: þ32 16 32 39 48; fax: þ32 16 32 45 75. E-mail address: Zahra.Geraylou@biw.kuleuven.be (Z. Geraylou). Contents lists available at SciVerse ScienceDirect Fish & Shellfish Immunology journal homepage: www.elsevier.com/locate/fsi 1050-4648/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fsi.2013.06.014 Fish & Shellfish Immunology 35 (2013) 766e775