Abstract:Here we conducted a feeding experiment to investigate the effects of Rhodotorula sp. C11 on the digestive enzyme activity and the immune response of juvenile Apostichopus japonicus, and to explore its potential use as probiotics in the aquaculture of sea cucumbers. Rhodotorula sp. C11 was added to the diets at the concentrations of 0 (control), 104, 105 and 106 CFU/g feed. The juvenile sea cucumbers were randomly allocated in 12 plastic tanks (100 L) with 50 individuals per tank. During the 30 day trial, all experimental sea cucumbers were fed one dose of diet per that weighed 5% of their body mass. At the end of the trial we measured the activities of the intestinal digestive enzyme and immunological parameters of the sea cucumbers. Data were analyzed with one-way analysis of variance (ANOVA) and Duncan's multiple comparison of the means with SPSS 19.0 software. A statistical difference was considered significant when P<0.05. It was shown that comparing to the control Rhodotorula sp. C11 at the concentration of 104 and 105 CFU/g feed significantly enhanced the activity of the intestinal trypsin, and at 104 CFU/g feed, Rhodotorula sp. C11 boosted the activity of amylase (P<0.05). Rhodotorula sp. C11 at the concentration of 105 CFU/g feed also increased the phagocytic activity in coelomocytes of sea cucumbers (P<0.05). Moreover, dietary Rhodotorula sp. C11 at the concentrations of 105 and 106 CFU/g feed significantly elevated the activities of lysozyme (LSZ) in the coelomic fluid, while that at 104 CFU/g feed increased LSZ activities in the coelomocyte lysate supernatant (CLS) respectively (P<0.05). Comparing to the control, the activity of total nitric oxide synthase (T-NOS) in the coelomic fluid was enhanced by Rhodotorula sp. C11 at 104 CFU/g feed, and the activity of this enzyme in CLS was elevated at 104, 105 and 106 CFU/g feed (P<0.05). Our results indicated that live yeast Rhodotorula sp. C11 could improve the activity of the intestinal digestive enzyme and activate the innate immune response of A. japonicus, therefore, it could potentially be used as an effective probiotic in sea cucumber farming.
