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Nile tilapia Oreochromis niloticus were produced in an experimental, on‐farm grow‐out cycle in which economic and production efficiencies were partially examined. Milled feeds were provided either daily (control) or on alternate days (experimental) at a given percentage of body weight, ranging from 20% initially to 2% at the end of the experiment. Growth, survival, feed conversion efficiency, cost, yield, and income were considered under the two strategies. Although the cost of feeds was cut in half by the experimental feeding treatment, feeding on alternate days did not reduce Nile tilapia growth or production performance variables, and yields were not significantly different. A trend favoring larger fish among the controls was not significant, and profit margins were higher for the alternate‐day feeding strategy than for the control strategy. Although feed conversion ratios varied considerably among the nine participating farms, the improved efficiency in the experimental groups was consistently observed and was statistically significant. It is possible that the improved performance attained by alternate‐day feeding is a result of reduced feed waste, either through more complete consumption of or improved nutrient absorption from available feeds.

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Tilapia–shrimp polyculture has played an important role in current efforts to control luminous bacterial disease caused by Vibrio harveyi. At present, green water technology is most extensively used by shrimp farmers in Negros Island in the central Philippines. While the contribution of tilapia as a biomanipulator is highlighted in the literature, the mechanism of action is not well understood. Data were gathered from shrimp ponds practicing two production systems: (a) green water system (probiotics + tilapia) and (b) closed/semiclosed system (probiotics alone). There was no difference between luminous Vibrio count (P < 0.05) in both systems, and water quality was found to be similar (P < 0.05). Because the green water system uses a bigger reservoir to raise the tilapia biomass, the net shrimp production was lower. In terms of direct cost of production, however, the green water system was 10–15% lower than the closed/semiclosed system because of significantly less aeration required. The polyculture maintained a more stable plankton environment during the early months of culture, which increased survival of shrimps. Various pathways are presented for the control of luminous bacterial growth in polyculture ponds: (a) fish feeding on organic wastes and conversion to feces; (b) selective fish foraging to increase the dominance of beneficial phytoplankton; (c) bioturbation of pond sediments; and (d) release in the water column of antimicrobials, fungi, or competing bacteria from the skin and gut mucus of tilapia.

No abstract