L.C. Tran-Tu^1,2 | T.T.T. Hien² | R.H. Bosma¹ | L.T.N. Heinsbroek¹ | J.A.J. Verreth¹ | J.W. Schrama¹

¹ Wageningen Institute of Animal Sciences, Aquaculture and Fisheries Group, Wageningen University, Wageningen, the Netherlands

² College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam

Correspondence: Johan W. Schrama, Wageningen Institute of Animal Sciences, Aquaculture and Fisheries Group, Wageningen University, Wageningen, the Netherlands. Email: johan.schrama@wur.nl 

The ingredients’ particle size and the dietary viscosity may alter digestion, performance and faecal waste management of fish. This study aimed to assess the effect of grinding screen sizes of the feed ingredients and dietary viscosity on digestibility, faecal waste and performance of striped catfish (Pangasianodon hypophthalmus, Sauvage, 1878).  The experiment had a 2x3 factorial design: two feed mash particle sizes, by grinding the ingredient mixture at two screen sizes (0.8 versus 1.0 mm); and three dietary viscosity levels, which were created by exchanging carboxyl methyl cellulose by guar gum (GG) (0, 3, and 6 g of GG kg^-1 of diet). The six diets were assigned to 18 tanks, each connected to three faecal settling tanks. All aquaria were stocked with 20 fish of 82 g fish^-1 on average. After 52 experimental days, dietary viscosity negatively affected both feed digestibility and performance of striped catfish; as a result the amount of organic matter in the culture system through faeces had increased significantly. The coarse diets significantly increased the digestibility of dry matter and carbohydrate but worsened feed conversion ratio. Increasing dietary viscosity tended to increase the viscosity and moisture content of the faeces, but significantly accelerated the faecal disintegration through the reduction of both faecal recovery and the amount of recovered faeces.