Effect of dietary Rhodotorula mucilaginosa on growth performance, digestive and immune enzymes activities of juvenile Nile tilapia (Oreochromis niloticus)

A growth trial was conducted to investigate the effect of dietary Rhodotorula mucilaginosa on the growth performance, digestive and immune enzymes activities of juvenile Nile tilapia (Oreochromis niloticus). Six diets were formulated by adding different levels of R.mucilaginosa to basal diet (control): 1 gkg-1, 2 gkg-1, 3 gkg-1, 4 gkg-1 and 5 gkg-1, respectively. The results show that compared with the control, the FCR of the fish in 2 gkg-1 and 4 gkg-1 groups decreased significantly (P0.05). The body crude protein of the fish in 5 gkg-1 group was significantly lower than those in 1 gkg-1 and 2 gkg-1 groups (P0.05). The body crude ash of the fish in 1 gkg-1, 3 gkg-1, 5 gkg-1 groups were significantly lower than that in control group (P0.05). Compared with the control, the pepsin activity of the fish in 1 gkg-1 Group increased significantly (P0.05), but the pepsin activities of the fish in 3 gkg-1, 4 gkg-1 and 5 gkg-1 groups decreased significantly (P0.05). The amylase activities in stomach, liver, foregut and midgut in 2 gkg-1 group were higher than those in control group significantly (P0.05). The lipase activities in foregut, midgut and hindgut in 2 gkg-1 and 3 gkg-1 groups than those in control group significantly (P0.05). Compared with the control, the hepatic lysozyme and nitric oxide synthase activities of the fish in 2 gkg-1 and 3 gkg-1 groups increased significantly (P0.05 ). In conclusion, the optimal dietary R.mucilaginosa level in juvenile tilapia feed could be 2～3 gkg-1.