The effects of xylanase and arabinoxylan-oligosaccharides on the growth performance, non-specific immunity, hindgut microbial diversity and hindgut short-chain fatty acid production of African catfish, Clarias gariepinus

Gericke, Stephan Johann (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Aquaculture is one of the fastest growing food-producing industries in the world, however, this industry is still highly dependent and relies more on the production of fishmeal and fish oil resources from marine capture fisheries than any other food producing industry. This trend has increased over the last few decades despite the stagnant production of capture-based fisheries. With the aim of becoming more sustainable, aquaculture feed producers have started to incorporate plant-protein ingredients as alternatives for fishmeal and fish oil. The principal challenge facing formulators when incorporating high levels of plant ingredients in aquafeeds is how to eliminate or even exploit the accompanying antinutritional factors, such as non-starch polysaccharides, while improving the low nutrient quality and digestibility of the plant ingredients. The aim of the study was to contribute to the global trend towards more sustainable aquaculture feeds by investigating the effect of two feed additives (endo-1,4-β-xylanase and an arabinoxylan-oligosaccharide-containing compound) to potentially improve the performance of formulated diets containing high levels of plant ingredients fed to African catfish, Clarias gariepinus. Liquid endo-xylanase (Nutrase Xyla) was obtained through Nutrex Belgium, while AXOS were thermochemically produced, through the method of steam explosion, from brewer’s spent grains, which is generally regarded as a waste product. In order to achieve the study’s aim, specific objectives were formulated and include the determination of i) a suitable inclusion level for both functional feed additives, as well as their effect on the ii) production performance parameters, iii) selected humoral non-specific immunity parameters, iv) hindgut microbial diversity, and v) hindgut short-chain fatty acid concentration of C. gariepinus fed highly plant-based diets. The study was comprised out of two independently run 91-day feedings trials, viz. xylanase and AXOS trials. Both trials consisted of four dietary treatments (a control and three test treatments) with each treatment replicated six times and receiving six randomly placed, mixed sex C. gariepinus at the start of each trial. The three test treatments of the xylanase trial each contained xylanase inclusion levels of 100, 150 and 200 PPM, respectively, while the test treatments of the AXOS trial each contained an AXOS-containing component at 0.3, 0.6 and 1.2%, respectively. Results from the xylanase trial showed that dietary xylanase was able to significantly decrease (P=0.041) the Shannon’s microbial diversity index of the xylanase 200 treatment compared to the control treatment. The control and xylanase 150 treatments also had a significantly higher Shannon’s diversity score compared to the pre-treatment group (sampled at Day 0). Furthermore, the control and xylanase 150 treatments had a significantly higher (P=0.050) Simpson’s diversity index compared to the pre-treatment group. During the course of the trial, dietary AXOS supplementation showed to significantly increase the immunoglobulin levels of fish fed the AXOS 0.6 and AXOS 1.2 treatments compared to the control and AXOS 0.3 treatment groups. At the end of the trial, the AXOS 1.2 treatment had a significantly higher (P=0.004) immunoglobulin level compared to all the other treatments. The study concluded that dietary xylanase was able to significantly decrease the hindgut microbial diversity of C. gariepinus based on a dose-dependent manner. The absence of any negative significant effect of the AXOS-containing compound on the growth and fillet composition proved that AXOS can be thermochemically produced from a waste product without the presence of semi-antinutritional factors. Additionally, AXOS significantly increased the immunoglobulin levels of C. gariepinus based on a dose-dependent manner. Overall, the supplementation of xylanase and AXOS in fishmeal-free diets of C. gariepinus may have promising potential as functional feed additives that may directly enhance the innate immunity of fish through interacting with the gut-associated lymphoid tissue or indirectly through the modulation of the hindgut microbiota.

AFRIKAANSE OPSOMMING: Akwakultuur is een van die vinnigste groeiende voedselproduksiebedrywe in die wêreld. Hierdie bedryf is egter steeds hoogs afhanklik van en berus meer op die produksie van vismeel- en visoliehulpbronne uit mariene vangsgebaseerde visserye as enige ander voedselproduksiebedryf. Hierdie tendens het die afgelope paar dekades toegeneem ten spyte van die stagnante produksie van mariene vangsgebaseerde visserye. Met die doel om meer volhoubaar te wees, het produsente van akwakultuurvoere begin met die opneming van plant-proteïen bestanddele as alternatiewe vir vismeel en visolie. Die vernaamste uitdaging vir formulateerders wanneer hoë vlakke van plantaardige bestanddele by akwakultuurvoere ingesluit word, is hoe om die gepaardgaande antinutrisionele faktore, soos nie-stysel polisakkariede, te elimineer of selfs te ontgin, terwyl die lae voedingskwaliteit en verteerbaarheid van die plantbestanddele verbeter word. Die doel van die studie was om by te dra tot die wêreldwye tendens na volhoubare akwakultuurvoere deur die effek van twee toevoegingstowwe (endo-1,4-β-xylanase en 'n arabinoxilan-oligosakkariedbevattende verbinding) te ondersoek om die prestasie van ‘n geformuleerde dieet met hoë vlakke van plantaardige bestanddele wat gevoer word aan Afrika-katvis, Clarias gariepinus, te verbeter. Xylanase en arabinoxylan-oligosakkariede (AXOS) het soortgelyke mikrobiese- en immunomodulatoriese eienskappe alhoewel hul doeltreffendheid ten opsigte van hierdie eienskappe in visvoere nog nie bewys is nie. Vloeibare endo-xylanase (Nutrase Xyla) is verkry deur Nutrex Belgium, terwyl AXOS termochemies van broueryse spandeerprodukte geproduseer is (algemeen beskou as 'n afvalproduk). Ten einde die doel van die studie te bereik, is spesifieke doelwitte geformuleer en sluit die bepaling van i) 'n geskikte insluitingvlak vir beide funksionele toevoegingstowwe in, asook hul effek op die ii) produksie prestasie parameters, iii) geselekteerde humorale nie-spesifieke immuniteit parameters, iv) agterderm mikrobiese diversiteit, en v) agterderm kortketting vetsuurkonsentrasie van C. gariepinus wat hoogs plantgebaseerde diëte gevoer is. Die studie het bestaan uit twee onafhanklike lopende 91-dae voedingsproewe, nl. xylanase en AXOS proewe. Beide proewe het bestaan uit vier dieetbehandelings ('n kontrole en drie toetsbehandelings) met elke behandeling wat ses keer herhaal is en wat ses willekeurig geplaasde gemengde seks C. gariepinus aan die begin van elke proefbeurt ontvang het. Die drie toetsbehandelings van die xylanase-proefneming het elk xylanase-insluitingsvlakke van onderskeidelik 100, 150 en 200 PPM bevat, terwyl die toetsbehandelings van die AXOS-proef elk 'n AXOS-bevattende komponent teen 0,3, 0,6 en 1,2% bevat het. Uit die xylanase-proefneming is bevind dat die xylanase dieet die Shannon mikrobiese diversiteitsindeks van die xylanase 200-behandeling aansienlik kon verlaag (P=0,041) in vergelyking met die kontrolebehandeling. Die kontrole en xylanase 150 behandelings het ook 'n aansienlike hoër Shannon diversiteitstelling behaal in vergelyking met die voorbehandelingsgroep (op Dag 0 gemonster). Verder het die kontrole en xylanase 150 behandelings 'n aansienlike hoër (P=0.050) Simpson diversiteitsindeks in vergelyking met die voorbehandelingsgroep gehad. Gedurende die verloop van die studie het die AXOS-aanvullings dieet getoon dat die immunoglobulienvlakke van die vis wat die AXOS 0,6- en AXOS 1.2-behandelings ontvang het, aansienlik verhoog is in vergelyking met die kontrole- en AXOS 0.3-behandelingsgroepe. Aan die einde van die studie het die AXOS 1.2-behandeling 'n aansienlike hoër (P=0.004) immunoglobulienvlak gehad in vergelyking met al die ander behandelings. Die studie het bevind dat die xylanase dieet in staat was om die agterderm mikrobiese diversiteit van C. gariepinus aansienlik te verminder, gebaseer op 'n dosisafhanklike wyse. Die afwesigheid van enige negatiewe beduidende effek van die AXOS-bevattende verbinding op die groei- en filetsamestelling het bewys dat AXOS termochemies van 'n afvalproduk geproduseer kan word sonder die teenwoordigheid van semi-antinutrisionele faktore. Daarbenewens het AXOS die immunoglobulienvlakke van C. gariepinus aansienlik verhoog op grond van ‘n dosisafhanklike wyse. Oor die algemeen kan die aanvulling van xylanase en AXOS in vismeelvrye diëte van C. gariepinus belowende potensiaal hê as funksionele toevoegingstowwe wat die aangebore immuniteit van vis direk kan verbeter deur interaksie met die derm-geassosieerde limfoïedweefsel of indirek deur die modulasie van die agterderm mikrobiota.

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