Effect of calcium hydroxide, carbonate and sodium bicarbonate on water quality and zootechnical performance of shrimp Litopenaeus vannamei reared in bio-flocs technology (BFT) systems

Litopenaeus vannamei (the Pacific white shrimp) is the most commonly reared species in super-intensive bio-floc technology (BFT) without water renewal. In BFT, the pH may decrease due to the reduction of alkalinity and the increase of dissolved carbon dioxide. This study evaluated the effects of calcium hydroxide, sodium carbonate and bicarbonate in maintaining water quality during the cultivation of L. vannamei in BFT. The experiment was conducted using juveniles stocked in 150-L 12 tanks at a density of 333 shrimp/m(3). There were four treatments with three replicates each: T1 - Na2CO3, T-2 - Ca(OH)(2), T-3 - NaHCO3 and T-4 - control. For pH correction, alkalinity and both pH and alkalinity corrections, we used sodium carbonate (0.06 g/L), sodium bicarbonate (0.20 g/L) and hydrated lime (0.15 g/L), respectively. Significant physical, chemical and biological differences (P<0.05) were detected among treatments. Control shrimps showed lower growth performance (P<0.05) than shrimps in other treatments. Hydrated lime and sodium bicarbonate appeared effective in supplementing alkalinity, whereas the soda ash did not. We verified the effectiveness of sodium carbonate in raising pH levels and assisting in supplementing alkalinity. This study demonstrates that the results obtained in the control treatment levels of alkalinity and pH decrease during rearing, and that CO2 levels would be increased in super-intensive systems with bioflocs without water renewal. (C) 2011 Elsevier B.V. All rights reserved.