s relating to farming are poorly understood. To assess the effects of co-cultured fish (grass carp, gibel carp, silver carp and bighead carp or silver carp and bighead carp) and formulated fish feed supplement (with or without feed supplement) on water chemistry characteristics, a 155-day field experiment was carried out in land-based enclosures. Four treatments including GGSB-F (co-cultured fish grass carp, gibel carp, silver carp and bighead carp were fed formulated feed), GGSB-NF (co-cultured fish grass carp, gibel carp, silver carp and bighead carp were not fed formulated feed), SB-F (co-cultured fish silver carp, and bighead carp were fed formulated feed) and SB-NF (co-cultured fish silver carp and bighead carp were not fed formulated feed) were established. The results indicated that the combination of co-cultured fish species could significantly affect Ca²⁺, total alkalinity (A) and total phosphorus (TP), while the feed supplement regime affected Ca²⁺, A, ammonia (TAN), TP and chemical oxygen demand (COD_Mn). Dissolved oxygen (DO) and Twere higher in the GGSB-F enclosures. Conversely, DO and SD were higher, but Ca²⁺were lower, in the SB-NF enclosures. During the experimental period, Ca²⁺ decreased, while TN, TP, TAN and COD_Mn increased. DO and SD were positively correlated with each other and negatively to the levels of TAN, TN, TP, Ca²⁺ and COD_Mn. Therefore, water qualityTAN and COD_Mn at the levels below the critical values, and maintaining Ca²⁺ and DO at high and constant levels.