Effect of carbohydrate source, feeding level (restricted vs. satiation) and their combination on nutrient digestibility, bile acid balance, faecal waste production and characteristics of yellowtail kingfish (Seriola lalandi)

The effect of carbohydrate source on nutrient digestibility, bile acid balance, faecal waste production and characteristics were investigated in yellowtail kingfish (Seriola lalandi). A starch diet and two non-starch polysaccharides (NSP) diets with different NSP sources were used in this study. A diet containing 12 % gelatinized wheat flour as the starch diet, and two diets with distinct non-starch polysaccharides (NSP) sources: soybean hulls (SH) and sugar beet pulp (SBP) at an inclusion level of 10 %, were studied. Each diet was tested in triplicate fish tanks. To determine if feeding level affects diet, restricted and satiation feeding levels were used. After four weeks of restrictive feeding, fish were fed satiation for two weeks. The dietary effect on nutrient digestibility and faecal waste production was dependent on feeding level, whereas the dietary effect on faecal waste characterises was independent of feeding level. SBP diet protein and fat digestibility was highest during restricted and satiation feeding. Satiation feeding reduced nutrient digestibility in all diets, most pronounced in SH and least in SBP. Faecal bile acid loss did not explain fat digestibility differences between the three diets. Both NSP diets increased faecal waste production but decreased bile acid content, resulting in similar bile acid loss to the starch diet. SBP had the highest faecal removal efficiency and the lowest non-removed faeces despite high waste production SH resulted in similar amount of non-removed faeces compared to the starch diet. To conclude, NSP type affected nutrient digestibility, bile acid balance, faecal waste production, and faecal characteristics differently than starch in yellowtail kingfish. Starch resulted in higher FCR and thus lower growth performance in yellowtail kingfish compared to NSP despite higher organic matter digestibility. Adding NSP to their RAS diet may improve faecal integrity without affecting macronutrient digestibility. However, different NSP forms affect nutrient digestion and faeces integrity differently.