The physico-chemical properties of nutrients in£uence the physical characteristics of faeces and thus may a¡ect waste removal e⁄ciency. The aim of this study is to assess the e¡ect of type of non-starch polysaccharide (NSP) on digesta viscosity, faeces recovery and nutrient digestibility in Nile tilapia. Insoluble (cellulose) and soluble (guar gum) NSPs were included separately and combined at a level of 8%, thereby formulating four experimental diets. The diets were assigned to 16 tanks with 35 ¢sh each, with four replicates for each diet. Cellulose inclusion did not in£uence digesta viscosity, growth and digestibility of protein and starch and tended to increase faeces recovery (P 5 0.06). Guar gum inclusion increased digesta viscosity and reduced the growth and digestibility of protein, fat and starch (Po0.01). Faeces recovery was reduced by 42% in diets containing guar gum. There were interaction e¡ects (Po0.05) between cellulose and guar gum for the growth and feed conversion ratio, indicating that cellulose alleviated the negative impact of guar gum. In conclusion, dietary soluble NSPs increase organic matter load in the culture system through a reduction in faeces recovery and nutrient digestibility, whereas insoluble NSPs improve the removal e⁄ciency of particles by increasing faeces recovery.

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The objective of the present study was to investigate if dietary soluble non-starch polysaccharides (NSP) increase digesta viscosity, reduce nutrient digestibility and increase organ weights in African catfish. The fish (mean weight 80 g) were fed diets supplemented with the soluble NSP guar gum at three levels, 0 g kg )1 (GG0), 40 g kg )1 (GG4) and 80 g kg )1 (GG8). Guar gum inclusion significantly increased digesta viscosity in the proximal (GG0: 1.7 centipoise or cP; GG4: 84.9 cP; GG8: 98.3 cP) and distal (GG0: 1.9 cP; GG4: 109.8 cP; GG8: 66.4 cP) intestine. Apparent digestibility coefficients (ADC) were significantly lower for the GG8 diet than the GG0 diet (dry matter: 52% versus 69%; protein: 77% versus 90%; ash: 41% versus 54%; energy: 60% versus 77%). The ADC of dry matter and energy were significantly lower for the GG4 diet than the GG0 diet. The relative growth rate of metabolic weight (14.5-15.4 g kg )0.8 day )1 ) and feed conversion ratio (0.8) did not differ between diets. Fish fed the GG8 diet had a significantly higher somatic stomach index than GG0 fish (0.71% versus 0.65% body weight). The intestinal somatic index tended to increase with increasing guar gum supplementation (GG0: 1.08%; GG4: 1.23%; GG8: 1.59%). In conclusion, high digesta viscosities in the guar gum fed fish may explain the observed reduced nutrient digestibilities and increases in digestive organ weights. KEY WORDS