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

Yellowtail kingfish (Seriola lalandi), a marine species, has recently been cultured in recirculation aquaculture systems (RAS). A challenge regarding faecal waste management of farming yellowtail kingfish in RAS is their poor faecal integrity. One approach to improve faecal waste management is to enhance nutrient digestibility and thus faecal waste production, which can be achieved through the addition of emulsifiers to the feed. We assessed the effect of emulsifier supplementation on nutrient digestibility, bile acid balance, faecal waste production and characteristics of yellowtail kingfish. This was investigated by using four experimental diets differing in emulsifier supplementation, where fish were fed restrictively (36 days). One diet without emulsifying supplements served as control. Three types of emulsifiers were tested (1) E484, composed of Glyceryl polyethyleneglycol ricinoleate; (2) Lysophospholipids (LPL) combined with lecithin; (3) Sodium taurocholate (STC). The results showed that the STC diet numerically improved fat digestibility and had a positive bile acid balance, which indicated an accumulation of dietary bile acids in the body bile acid pool. Despite a negative bile acid balance, the LPL diet improved fat digestibility as well. A negative bile acid balance shows that the daily amount of faecal bile acid loss exceeds the daily amount of dietary bile acid intake. Fish fed the E484 diet had more faeces removed than the other diets, whilst non-recovered faeces or faecal characteristics were not affected. In conclusion, the current study shows that supplementing both sodium taurocholate (STC), and the combination of Lysophospholipids (LPL) and lecithin can improve fat digestibility in yellowtail kingfish, but emulsifier supplementation does not improve faecal waste management.