Physical feed properties affect gastrointestinal passage rate in Atlantic salmon, Salmo salar

Physical feed properties affect feed utilization in fish. To study how physical feed properties affects feed intake, digestibility and gastrointestinal passage, two feeds with identical formulation, but different physical properties, were produced. Diet 1 was produced with lower water stability than Diet 2. Each feed was produced in three batches, added lanthanum (La), ytterbium (Yb) or yttrium (Y) as indigestible markers. The feeds were fed to Atlantic salmon (1,047 g), one daily meal, for 29 days. Feeds labelled with La were used the first 26 days, feeds with Yb on day 27 and feeds with Y on days 28 and 29. Faeces were collected 8, 16, 24, 32, 40 and 48 hr after feeding on day 27 and analysed. La, Yb and Y in faeces originated from feed eaten on days 26, 27 and 28, respectively. Marker concentrations in faeces showed that some Yb appeared in faeces 8 hr after feeding. After 16 hr, the passage rate was higher for Diet 1 than Diet 2. After 48 hr, both feeds had passed almost completely through the gastrointestinal system. The apparent digestibility of lipid was higher in Diet 1 than in Diet 2. There was no significant difference in feed intake.