The digestibility trial was conducted in another re-circulating water system with 18 tanks as described by Peres and Oliva-Teles (2002). 40 fish (mean body weight of 30 g) were distributed to each tank, and three tanks were randomly arranged and assigned to each diet. Yttrium oxide (0.01%) was used as the external indicator in the six experimental diets. After two weeks acclimation, feces from each replicate were collected by siphoning 6–7 h after feeding. Briefly, once feces were observed, they were immediately collected by gently siphoning, dried for 12 h at 50 °C and stored at − 20 °C until analysis. Fecal collection continued for four weeks until 5 g dry weight of fecal material had been sufficiently collected for chemical analysis.