C:N ratios affect nitrogen removal and production of Nile tilapia Oreochromis niloticus raised in a biofloc system under high density cultivation

Over a six-month trial, growth performance of juvenile tilapia Oreochromis niloticus, raised under biofloc cultivation, was recorded. Five treatments with three replicates and 237 juveniles per replicate at different C:N ratios were tested (10:1, 12.5:1, 15:1, 17.5:1, 20:1). Molasses was added every fourth day as the carbon source. Trials were performed in eighteen 3.14 m(3) circular tanks with constant aeration. Survival in all treatments with biofloc was similar and significantly higher (94.60 +/- 2.03%) than in the control treatment (84.96 +/- 1.53%). Best weight gain (g/day) occurred in the control treatment, but was influenced by low density. The 10:1 and 15:1 C:N treatments had similar weight gains, but not the 12.5:1 and 17.5:1 C:N treatments. Total production in the 10:1 ratio treatment was the highest (18.03 +/- 0.25 kg m(-3)), with slightly declining production, in this order: control (17.86 +/- 0.16), 15:1 (17.73 +/- 0.18), 12.5:1 (17.20 +/- 0.28), 17.5:1 (16.44 +/- 0.04), and 20:1 (16.28 +/- 0.02). Water quality remained similar in all biofloc treatments, but lower concentrations of nitrogen compounds occurred in the 10:1 C:N ratio tanks. These results suggest a 10:1 C:N ratio provides good survival and growth of tilapia with no water exchange. Biofloc technology is a good strategy in areas where alkaline pH is a limiting factor for aquaculture activities because the pH decreases gradually as molasses is added. Statement of Relevance: The success and permanence of aquaculture sector relies on the implementation of sustainable and environment-friendly technology, the BFT optimizes energy and resources during production, so our results contribute significantly to the sector. (C) 2015 Elsevier B.V. All rights reserved.