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

[摘要] 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.

[发布机构] Stellenbosch University