A 3-month enclosure experiment was carried out to examine the effects of different stocking (monoculture of freshwater pearl mussel Hyriopsis cumingii, polyculture of the pearl mussel and gibel carp Carassius auratus gibelio, and polyculture of the pearl mussel, silver carp Hypophthalmichthys molitrix and bighead carp Aristichthys nobilis) and management (fertilizing, combination of fertilizing and feeding) models on chemical water quality. During the experiment, mean value of dissolve oxygen (DO) in the enclosures was over 8.9 mg·L-1, and pH ranged from 6.99 to 10.69. The enclosures with monoculture of the pearl mussel had high DO and pH. Mean value of Ca2+, hardness and alkalinity in the enclosures ranged within 15.6-23.2 mg·L-1, 80.6-96.6 mg CaCO3·L-1 and 72.1-89.1 mg CaCO3·L-1, respectively. Mean value of nitrate (NO3-N), nitrite (NO2-N), ammonia (TAN), reactive phosphate (PO4-P), total nitrogen(TN) and total phosphorus (TP) ranged within 0.115-0.202 mg·L-1, 0.002 -0.005 mg·L-1, 0.088-0.163 mg·L-1, 0.018-0.055 mg·L-1, 1.906-2.989 mg·L-1 and 0.327-0.539 mg·L-1, respectively. There were no significant differences in NO3-N, NO2-N and TAN among the enclosures. High PO4-P occurred in the enclosures in which the pearl mussel and gibel carp were polycultured with fertilizing and feeding or the pearl mussel was monocultured with fertilizing. TN and TP were high in the enclosure in which the pearl mussel was monocultured with fertilizing and feeding. Mean value of (NO3-N+NO2-N+TAN )/PO4-P in each enclosure ranged from 9 to 18, and TN/TP from 6 to 8, respectively. No significant difference was found in ( NO3-N+NO2-N +TAN)/PO4-P and TN/TP among the enclosures. Mean value of chemical oxygen demand (CODMn ) ranged from 17.29 to 17.33 mg·L-1 in the enclosures of monoculture, and from 11.21 to 13.91 mg·L-1 in the enclosures of polyculture. TN and CODMn increased, while TP decreased, with advance of the experiment. Results of the present experiment indicate using different stocking and management models could not
