Application of different doses of calcium hydroxide in the farming shrimp Litopenaeus vannamei with the biofloc technology (BFT)

The reduction in alkalinity and pH occurs due to the consumption of inorganic carbon by bacteria present in the biofloc. The objective of the study was to evaluate the effects of different doses of calcium hydroxide on the water quality and growth performance of the Litopenaeus vannamei in a biofloc system. The experiment consisted of four treatments with three repetitions for each treatment: Control treatment (TC), in which the pH maintained above 7.2 due to the application of 0.05 g L^?1 of calcium hydroxide, and treatments T10, T20 and T40, in which daily doses of calcium hydroxide equivalent to 10, 20 and 40 % of the total amount of feed offered to the shrimp, respectively, were added to the environment. Twelve experimental units (150 L) were stocked with 85 juveniles of L. vannamei (0.18 ± 0.06 g), corresponding to a density of 425 shrimp m^?3, and cultivated for 56 days. The values of alkalinity and pH for treatments TC and T10 were similar and significantly lower (p < 0.05) than those for treatments T20 and T40, which differed (p < 0.05) between each other. In terms of growth performance, TC, T10 and T20 performed significantly better (p < 0.05) than T40. There were no significant differences (p > 0.05) in the survival rates. The results obtained indicate that doses of 0.05 g L^?1 of calcium hydroxide or daily applications between 10 and 20 % of the total amount of feed offered to the shrimp can be used for the correction of alkalinity and pH.