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Clementain C Zvavahera, Vimbai R Hamandishe, Petronella T Saidi, Venancio E Imbayarwo, Tamuka Nhiwatiwa

The aim of this study was to determine the effect of greenhouse culture conditions on water quality variables that are important for tilapia aquaculture. Six experimental ponds, three in open atmosphere and three under greenhouses were set up. Each pond was further subdivided by hapas to make 12 experimental units of which half were stocked with Oreochromis niloticus and the other Oreochromis macrochir. Water was sampled fortnightly from each pond for chemical and physical quality assessment. Water temperature, conductivity, turbidity, total dissolved solids, dissolved oxygen and pH, were determined in-situ over a period of 24 hours. The following chemical variables were also analysed: biological oxygen demand, chemical oxygen demand, alkalinity, chlorides, chlorophyll a, nitrates, total phosphorus, reactive phosphorus, total suspended solids and ammonia. Water temperatures, chlorophyll a and reactive phosphorus concentrations were significantly higher in the greenhouse ponds than in the open ponds. Otherwise, the concentrations of all the other chemical water variables were not significantly different between greenhouse and open ponds both before, and after the rainfall season. This study revealed that modification of the culture conditions for tilapia production, greatly influenced physical water variables important for fish growth, but had little effect on the chemical variables.

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