Abstract
The main effects and synergy between three enzymes (phytase, xylanase and β-glucanase) on growth performance and nutrient digestibility was explored in Nile tilapia (Oreochromis niloticus). This was done according to a 2 × 2 × 2 factorial arrangement, resulting in 8 dietary treatments. In total 24 tanks (3 replicates per treatment) were used with 30 fish each (mean initial body weight 38 g (SD ± 0.8)). In a 42 day experiment growth and nutrient digestibility were measured. Fish were restrictively fed by hand twice daily. Phytase affected the nutrient digestibility, improving the ash, phosphorus and calcium digestibility. Neither individual enzymes supplementation, nor their combinations, did affect absolute growth (g/d). Averaged over diet, the feed conversion ratio (FCR) was low (0.92) despite 140 g/kg non-starch polysaccharides (NSP) in the diets. A comparison with previous studies, which used comparable diets and enzyme treatments was made to elaborate on the minor effects of enzyme supplementation in the present study. The response of fish fed the diet with phytase and xylanase was comparable between studies. However, the control treatments without enzymes in the present study had a lower FCR and higher dry matter (DM) and NSP digestibility compared to previous studies. The current control diet was more comparable to the diets supplemented with enzymes in previous studies. It is likely that in the present study, and other studies that do not show improvement in growth with the use of enzymes, the control diets were not sufficiently limiting in nutrients for growth.
Highlights
The expansion of the aquaculture sector has been accompanied by rapid growth of aqua feed production
Other studies showed an improvement on growth performance with the use of non-starch polysaccharides (NSP)-degrading enzymes and phytase (Adeoye et al, 2016a,b; Ai et al, 2007; Ghomi et al, 2012; Jiang et al, 2014; Lin et al, 2007; Maas et al, 2018; Yildirim and Turan, 2010; Zhou et al, 2013)
The diet used in the presented study is the same diet as the wheat bran (WB) diet described in Maas et al (2019), on referred to as experiment 2
Summary
The expansion of the aquaculture sector has been accompanied by rapid growth of aqua feed production. The input of wild fish for the production of farmed fish is decreasing, leading to an increasing use of plant ingredients, such as soybean, wheat and corn in aqua feeds (Naylor et al, 2009; Pahlow et al, 2015). Negative effects observed of using plant ingredients are mainly due to the presence of a range of anti-nutritional factors (ANF) like saponins, tannins, phytates, lectins, protease inhibitors, non-starch polysaccharides (NSP) (Francis et al, 2001; Sinha et al, 2011). In particular by-products (i.e., hull meals) can contain high levels (>50 %) of poorly digestible NSP
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