The feasibility of Chinese mitten crab (Eriocheir sinensis), mandarin fish (Siniperca chuatsi), and mud carp (Cirrhinus molitorella) polyculture and their effects on growth performance, water quality, antioxidant, and nonspecific immunological capacity

In recent years, polyculture has been used to satisfy the increasing demand for aquatic food. In addition, polyculture can promote the efficient use of water and encourage nutrient recycling and has great economic potential. However, limited information has been reported on detailed comparisons between monocultures and polycultures of Eriocheir sinensis in ponds thus far. Therefore, we conducted a 75-day experiment to compare the water quality, health status, production, and growth performance of E. sinensis in mono- and polyculture groups. Three treatments, namely, E. sinensis monoculture (T1), Siniperca chuatsi monoculture (T2), and E. sinensis, S. chuatsi, and Cirrhinus molitorella polyculture (T3), with 5 replicates each, were conducted in indoor concrete ponds. In T3, E. sinensis was fed commercial sinking pellets (36% crude protein) once a day at 5:30 pm, just an hour following C. molitorella, which was fed a fish diet (15% crude protein). The results showed that the total production in T3 reached 0.68 +/- 0.54 kg/m(2), which was significantly higher than that in T1 (0.43 +/- 0.66 kg/m(2)) and T2 (0.22 +/- 0.21 kg/m(2)) (P < 0.05). The survival rates of E. sinensis and S. chuatsi did not vary among treatments (P > 0.05). The growth performance (body weight, SGR) of female E. sinensis and S. chuatsi indicated no significant differences among treatments (P > 0.05), while male E. sinensis performed significantly better in T3 than in T1 (P < 0.05). The antioxidant capacity (SOD, CAT) and nonspecific immunity (ALP, ACP, and LSZ) of E. sinensis and S. chuatsi were significantly higher in the monoculture groups (P < 0.05). In addition, principal component analysis (PCA) demonstrated a higher concentration of total nitrogen (TN) and total phosphorus (TP) in T1 than in T2 and T3. Moreover, the permutational multivariate analysis of variance (PERMANOVA) revealed that the water quality in T1 significantly differed from that in T2 and T3 (P < 0.05), and there were no significant differences between T2 and T3 (P > 0.05). Stable isotope analysis (SIA) showed a shift in E. sinensis diets when introducing S. chuatsi and C. molitorella in T3. Polyculture of E. sinensis, S. chuatsi, and C. molitorella in the same pond improved water quality and led to higher total production and better growth of E. sinensis but weakened their antioxidant capacity and nonspecific immunity. Based on the present results, application of such a new method in conjunction with an appropriate feeding strategy proved to be a more productive, environmentally friendly, and promising aquaculture model.