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The study analysed the dose–response relationship between dietary viscosity and nutrient digestibility, faecal waste characteristics in striped catfish and the long-term impacts of viscosity on performance of striped catfish. This was done in two experiments: Exp.1 lasted 29 days, in which six dietary viscosity levels were created by including different amount of guar gum (GG; 0, 0.25, 0.5, 1.0, 2.0 or 3.0 g/kg) and Exp.2 lasted 60 days and assessed the long-term effects of three dietary GG levels (0, 0.5 and 3.0 g/kg) were checked. In Exp.1, digestibility of nutrients (except crude fat) decreased linearly with dietary viscosity. With increasing viscosity, removal efficiency of faeces from the water reduced linearly, whereas the total amount of faeces produced and the fraction of big-sized faecal particles (>2 mm). increased linearly. In Exp.1, viscosity did not affect performance. However, in Exp.2, the GG inclusion level of 3.0 g/kg (1.72 cP for the viscosity) affected fish performance. In conclusion, the best strategy for faecal waste management in striped catfish by dietary viscosity is to keep it as low as possible in the diet.