Influence of ambient oxygen on feeding and growth of the tilapia, Oreochromis niloticus (Linnaeus)
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Oreochromis niloticus (8.1 ± 0.5 g) grown in fresh water at 28 ± 2C for 35 days at various ambient oxygen concentrations, below air saturation in static water aquaria, were seriously affected in their feeding, assimilation and growth by ambient oxygen. While the ambient oxygen maintained was reduced from about 90% air saturation (about 7 mg/l) to about 20% air saturation (about 1.5 mg/l) food consumed and assimilated decreased 40 and 60% respectively. Correspondingly, assimilation efficiency dec reased from 80 to 50%, and conversion efficiency from 15 to 5%, while uncorrected FCR increased from 1.45 to 6.75. Under a simulated diel flux of oxygen (from about 20 to 200% air saturation) brought about by an induced bloom of plankton, growth rate of O. niloticus was considerably reduced when compared with those maintained at DO near saturation constantly. The present results suggest that DO levels below about 50% air saturation and diel flux of DO, often prevalent in tropical fish ponds tr eated with high doses of organic/inorganic fertilizers, would cause considerable reduction in pond production of tilapias.