Analysis of the cost-effectiveness and growth of Nile tilapia (Oreochromis niloticus) in biofloc and green water technologies during two seasons

Abstract

The effect of biofloc (BFT) and green water (GWT) technologies on the performance of Nile tilapia (Oreochromis niloticus) was studied during the rainy (RN) and dry (DR) seasons. The temperature range during RN was 18.9 °C to 31.5 °C, while during DR, it was 20.3 °C to 34.2 °C. Average precipitation during RN and DR was 94.5 ± 77.0 mm and 78.1 ± 46.5 mm, respectively. The fish were reared (42 fish/m3) in outdoor geomembrane tanks (113 m3), from 32.71 ± 3.57 g to the market size of 450 ± 50 g. Three tanks were used for each technology. The feed was reduced by 25% in the BFT tanks. The season significantly affected the growth of fish in both technologies. The fish showed a better hematological profile during RN, compared to DR. The rate of daily growth in RN-GWT was 0.55 g higher (2.97 g/d) than that in DR-GWT (2.42 g/d), and the fish attained the market weight four weeks earlier. For every USD invested in RN-GWT, a profit of 0.73 USD/kg was obtained, compared to 0.46 USD/kg that was obtained during DR. Mortality in RN-GWT was 2.4% higher than in DR, due to excess nitrite. During RN, BFT was more affected than GWT due to the difficulty in maintaining a stable C:N ratio (10:1). A 25–30% reduction in diet did not affect growth rate and survival, while significantly improving the profitability. The RN-BFT fish attained market weight within 168 days, 30 days less than fish raised during DR. Maintaining suspended solids for 168–205 days in BFT required electrical energy expenditure that was 50.2%–60.5% more compared to GWT. The best performance was obtained in RN-GWT, where the fish attained market size within minimum harvest time (145 days), with a lower FCR (1.27), thus obtaining the highest gross yield (17.4 kg/m3) and a contribution margin of 48.1%.