Effects of arabinoxylan-olligosaccharides (AXOS) and endogenous probiotics on juvenile Siberian sturgeon (Acipenser baerii)
The growth of industrial aquaculture has accelerated over the past decades. Next to the many positive outcomes this has unfortunately also resulted in environmental damages and emerging diseases. The need for increased disease resistance, optimum growth and feed efficiency has brought about the use...
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| Other Authors: | , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
2013
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| Online Access: | https://lirias.kuleuven.be/handle/123456789/414854 https://lirias.kuleuven.be/bitstream/123456789/414854/1//final+thesis+3.pdf |
| Summary: | The growth of industrial aquaculture has accelerated over the past decades. Next to the many positive outcomes this has unfortunately also resulted in environmental damages and emerging diseases. The need for increased disease resistance, optimum growth and feed efficiency has brought about the use of pre-/probiotics in aquaculture practices.The potential of different concentrations and structures of arabinoxylan-oligosaccharides (AXOS), a newly discovered class of candidate prebiotics, was investigated in juvenile Siberian sturgeon (Acipenser baerii) through two independent in vivo experiments. In the first trial, the impact of 2% and 4% AXOS-32-0.30 with average degree of polymerization of 32 (avDP) and an average degree of substitution of 0.30 (avDS), was tested. Ten weeks feeding of fish with 2% AXOS-32-0.30 showed higher weight gain (WG) and specific growth rate (SGR), although not significantly different from the control and 4% AXOS treatments (p>0.05). The feed conversion ratio (FCR) of sturgeon fed 2% AXOS-32-0.30 was significantly lower than fish fed the control diet. The survival rate of fish fed 2% AXOS-32-0.30 was also significantly higher compared to fish fed 4% AXOS-32-0.30 (p<0.05).The second trial was set up to test the impact of two different preparations, namely AXOS-32-0.30 and AXOS-3-0.25, at a level of 2% for 12 weeks. Growth performance and feed utilization tended to increase in sturgeon fed a diet supplemented with AXOS-32-0.30, however not significant (p>0.05). The effects of different concentrations and structures of AXOS on gut microbiota composition was evaluated using 454-pyrosequencing with barcoded primers targeting the V3 region of the 16S rDNA and PCR-denaturing gradient gel electrophoresis (PCR-DGGE). Redundancy analysis based on the relative abundance of the OTUs or DGGE band intensities revealed that in both trials hindgut community composition clustered significantly according to feed type. Supplementation of 2% AXOS-32-0.30 in sturgeon diet did not alter overall hindgut bacterial diversity in juvenile A. baerii in terms of bacterial species richness and Shannon diversity, while feeding A. baerii a diet supplemented with 2% AXOS-3-0.25 resulted in an increase of hindgut bacterial diversity. The consumption of 2% AXOS-32-0.30 increased the relative abundance of Eubacteriaceae, Clostridiaceae, Streptococcaceae and Lactobacillaceae, while the abundance of Bacillaceae was higher in response to 4% AXOS-32-0.30. The abundances of Lactobacillus spp. and Lactococcus lactis were greater after 2% AXOS-32-0.30 intake. DNA sequencing of the dominant DGGE bands recovered from the different treatments showed that AXOS mainly stimulated the growth of lactic acid bacteria and Clostridium spp., with more pronounced effects of AXOS-32-0.30. Assessment of fermentation activity in sturgeon hindgut showed that the production of acetate, butyrate and total short chain fatty acids increased in fish fed 2% AXOS-32-0.30. AXOS was also ableto enhance theinnate immune responses of Siberiansturgeon. Both AXOS-32-0.30 and AXOS-3-0.25 (2%) significantly enhanced the phagocytic activity of fish macrophages compared to the control group, while the alternative haemolytic complement activity and total serum peroxidase content improved only in the group fed AXOS-32-0.30.The selection and characterization of putative endogenous probiotics was another objective of this study. To select and characterize potential probiotic bacteria from gut microbiota of Siberian sturgeon, some 129 strains isolated from the hindgut were screened for antagonistic activity against five most common fish pathogens. Ten out of those strains showed antagonismtowards three or more pathogens. These isolates were identified using genetic, phenotypic and biochemical traits, and further characterized by in vitro testing, assessing the adhesion and growth in mucus and the resistance to gastric and intestinal fluids. Through an in vivo study, the candidate probiotics were characterized as being non-pathogenic. Based on all these assays, Lactococcus lactis ssp. lactis ST G45 and ST G81 showed the broadest inhibitory potential as well as a high viability in simulated gastrointestinal juice and the highest adhesion capacity to mucus. They were selected as the most promising candidate probiotics for in vivo test condition. As Bacillus spp. are able to form spores, they can easily be applied as probiotics. Therefore, in addition to two strains of L. lactis, the probiotic potential of B. circulans ST M53 was also tested in vivo.The effects of administration of putative endogenous probiotics Lactococcus lactis spp. lactis or Bacillus circulans, alone and in combination with 2% AXOS-32-0.30 were investigated in juvenile A. baerii. After four weeks, growth performance and feed conversion ratio significantly improved in fish fed a diet containing L. lactis spp. lactis ST G45 +AXOS. According to statistical analysis, no interaction between AXOS and probiotics was found and therefore the significant improvement in fish growth performance after simultaneously adding L. lactis spp. lactis ST G45 and AXOS can be considered as a cumulative outcome of the improvements observed when L. lactis spp. lactis ST G45 and AXOS are applied separately. Innate immune responses of sturgeon were boosted with both AXOS and probiotic diets. Synergistic effects of AXOS and probiotic diets on immune responses were only observed for phagocytic and alternative complement activity. Phagocytic and respiratory burst activity of macrophages increased in fish fed a diet containing AXOS or diet containing L. lactis spp. lactis ST G45 +AXOS. Humoral immune responses only increased in sturgeons fed L. lactis spp. lactis ST G45 +AXOS. Pyrosequencing analysis (16S rDNA) of the hindgut microbiota demonstrated that AXOS improvedthe colonization or/and growth capacity of L. lactis, as a higher relative abundance of L. lactis was observed in fish receiving a diet containing L. lactis spp. lactis ST G45 + AXOS than the group receiving only L. lactis spp. lactis ST G45. No observable number of B. circulans was found in the hindgut of sturgeon fed a B. circulans containing diet or AXOS+B. circulans. The dietary L. lactis spp. lactis ST G45 + 2% AXOS caused significant alterations in the intestinal microbiota by decreasing the bacterial diversity, as demonstrated by the fall in richness and Shannon diversity due to synergism between AXOS and L. lactis.It is concluded that the effects of AXOS on juvenile A. baerii are dose and structure dependent. AXOS with a relatively higher degree of polymerization (AXOS-32-0.30) has potential to be introduced as a prebiotic in the feed of Siberian sturgeon, due to stimulation of L. lactis and Lactobacillus spp, increasing of short-chain fatty acids and boosting immune responses. Moreover, the ability of L. lactis ssp. lactis ST G45 to survive/colonize in the intestinal microbiota and to act as a potential probiotic strain was demonstrated. The combined administration of 2% AXOS-32-0.30 + L. lactis spp. lactis ST G45 resulted in improvement of growth and immune responses of A. baerii and important alterations in the intestinal microbiota by a significant decrease in bacterial diversity and increase of the relative abundance of lactic acid bacteria. These results open perspectives for an economic application of AXOS combined with selected probiotics in Siberian sturgeon aquaculture. status: published |
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