The effect of water exchange on water quality, plankton abundance, and the production of koi carp, Cypńnus carpio var. koi L., cultured in outdoor concrete tanks manured with poultry excreta was determined. Individual weight gain and survival rates of fish (initial weight 0.09 ± 0.02 g) were compared among five culture regimes, where a volume of 100 dm³ water was exchanged: (1) every day (WEI); (2) every alternate day (WE2); (3) two times a week (WE3); (4) once a week (WE4); and (5) a control treatment with no water exchange (NE). Significandy higher concentrations (P < 0.05) of conductivity, NH₄ -N, NO₂ -N, NO₃ -N, PO₄ -P and bicarbonate alkalinity were recorded in the NE treatment. Plankton volume was highest in WEI (P < 0.05). The weight gain and number of koi carp of marketable size were significantly higher (P < 0.05) in WEI. There was a significant difference in the survival of koi carp among the treatments ranging from 60.43% (NE) to 95.21% (WEI). The results suggest a water exchange of 100 dm³ daily (WEI) was the most effective for koi carp tanks manured with poultry excreta as better water quality and greater plankton abundance were both maintained in the system.
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