Effect of non-starch polysaccharides and bile acid supplementation on nutrient digestibility, bile acid balance, faecal waste production and characteristics of yellowtail kingfish (Seriola lalandi)

Effects of non-starch polysaccharides (NSP) and bile acid supplementation (sodium taurocholate, STC) on nutrient digestibility, bile acid balance, faecal waste production and characteristics were investigated in yellowtail kingfish (Seriola lalandi). The experiment was conducted according to a two-by-two factorial design. Four diets were tested, differing in NSP level (CON vs. NSP) and bile acid supplementation (0 % STC vs. 0.4 % STC). The NSP level was altered by the inclusion of either 0 % or 10 % of NSP-rich ingredient mixture, which consisted of wheat bran and soy hull (1:1). Bile acid supplementation was tested by adding either 0 % or 0.4 % STC to the diets. Each dietary treatment was tested in triplicate. Fish were fed to apparent satiation for 32–33 days. Results showed that both the dietary inclusion of NSP and STC increased feed intake of yellowtail kingfish. NSP inclusion had no negative effect on nutrient digestibility. It even improved phosphorus digestibility and tended to increase protein digestibility. STC supplementation improved fat digestibility, independent of NSP level. Dietary STC supplementation increased the size of bile acid body pool, but inhibited bile acid synthesis. Regarding faecal waste, the NSP-supplemented diets had higher faecal waste production but also a higher faecal removal efficiency, resulting in more faecal waste removed faeces than the CON diets. As a result, at both diets (CON and NSP) the amount of non-removed faeces was similar. STC supplementation had no effect on faecal waste production and faecal characteristics. In summary, our results showed that yellowtail kingfish (a carnivorous species) copes well with NSP regarding feed intake and nutrient digestibility. Bile acid supplementation can enter the body bile acid pool and improve fat digestibility of yellowtail kingfish, which can be an effective way to secure proper fat digestion when fed plant-based diets. Regarding faecal waste, a small amount of NSP in the diets results in a large portion in the faeces, which may play an important role in determining faecal characteristics and removal efficiency. Considering its effects, incorporating small amounts of NSP into the feed can be helpful for effective faecal waste management in RAS fish.