Feed binders to improve the quality of Atlantic salmon (Salmo salar) feed and faeces

Binders are commonly incorporated into aquafeeds to improve pellet durability during transport and handling, as well as to enhance water stability. These functional properties may also affect faecal characteristics, which are critical for efficient removal of solid waste in aquaculture systems. Two control feeds were formulated: one fish-meal-based feed (FM, 60% FM) and one plant-meals-based-feed (PM, with 15% FM). An additional 14 PM-based feeds were produced by including one of the following binders; guar gum, xanthan gum, lignin sulfonate, potato starch, pea starch, alginate or gelatine-at 2 or 5%. Atlantic salmon postsmolt were fed these feeds in two preliminary trials: Trial 1 compared the PM control with feeds containing 2% binders, and Trial 2 compared FM control with feeds containing 5% binders. In Trial 1, faecal material could only be collected from fish fed 2% guar gum, whereas faeces were collected from all groups in Trial 2. Based on these results, the FM control, PM control and feeds containing 2% guar gum, xanthan gum and alginate were selected for a final trial (Trial 3). Significantly more faecal material was collected from salmon fed guar gum, followed in descending order by FM control > alginate > xanthan gum > PM control. Guar gum also resulted in significantly lower nutrient digestibility and, together with xanthan gum, increased intestinal viscosity and decreased faecal dry matter content compared to the control feeds (PM < FM). Faeces from fish fed the FM control contained less carbohydrates and more ash than faeces from PM-based feeds, which may have contributed to differences in faecal stability and should be investigated further.