Upgrading low-quality feeds for tilapia by enzyme and probiotic supplementation

Abstract

various Bacillus strains, metabolise VFA and might work better, over a longer period, in a VFA-rich gut.Enzymes and probiotics are administered through the diet, therefore it is likely that diet-related factors will play a major role in their desired effect. However, in studies testing the effect of enzymes or probiotics, a single (basal) diet is generally used. Therefore, it remains unclear how diet-related factors may affect the efficacy of enzymes and probiotics. As enzymes are specific for certain substrates it can be expected that the composition of the targeted fractions, in this case NSP and phytate, may affect the response to dietary enzyme supplementation. It can also be expected that when the diet is of low quality (i.e. low digestibility), or when ANF are expressed more, there is a greater potential for improvement with enzyme and probiotic supplementation. Aim and outline of the thesisThis thesis foresees the increasing importance of under-utilised crop waste in formulated aquafeeds and their positive contribution to the 'bio economy'. Indeed, one of the main goals in the context of circular food production is to formulate aquafeeds with improved digestibility, containing plant ingredients that would otherwise be wasted (FAO, 2020). This will allow for a more sustainable growth of aquaculture. The general aim of this thesis is to investigate whether the nutritional value of low quality diets can be improved, with the use of exogenous enzymes and probiotics, using tilapia as a model species. The leading questions addressed in this thesis are: Is tilapia able to "digest" and utilise NSP endogenously?  Can dietary probiotics and enzymes (phytase and carbohydrases) supplementation improve nutrient digestibility and utilisation?  Are there interactions between enzymes (mutually) and probiotics?  Do diet-related factors (quality, levels of ANF, composition etc.) have an effect on the response to enzyme supplementation?The objective of this research is to allow for the increased use of low-quality crop residues in aquafeeds, which will contribute to the development of circular food systems.

Protein evaluation in fish: African catfish as a case study

“…In fish, only few studies have investigated diet-elicited effects on digestion of nutrients in different compartments of the GIT (i.e., stomach, proximal-, mid-and distal intestine) (Harter et al, 2015;Harter et al, 2013;Leenhouwers et al, 2007a;Maas, 2021;Tran-Tu et al, 2019). Dietary fat replacement by starch reduced protein disappearance in the stomach (Harter et al, 2015), which coincided with a lower stomach dry matter content and increased water influxes in the stomach of African catfish (Clarias gariepinus) (Harter et al, 2015).…”