Different C:N ratio approaches in biofloc system for Pacific white shrimp

We evaluated two C:N ratio in this experiment.

The first one, was an heterotrophic system with C:N ratio of 15:1. Three days before stocking, water was fertilized with feed and white sugar at carbon/nitrogen ratio (C:N) of 15:1 in order to reach 200 mg L-1 of total suspended solids (TSS) at the beginning of the rearing period. During the experiment, when total ammonia nitrogen (TAN) surpassed 1 mg·L-1, extra sugar was added to the system at a ratio of 20 g of sugar per each gram of TAN.

For the second one, we use a C:N ratio of 8,9, with inoculation of water from a mature tank. The experimental tanks of the mature biofloc treatment (n = 4) were by mixing 90 L of water from a biofloc tank stocked with shrimp (30%; matrix tank) and 210 L of seawater. The matrix tank was a 9 m3 circular tank stocked with 300 adult shrimp m-3 (weight = 21.3 ± 0.52 g). Water quality parameters of matrix tank were as follows: salinity 37 g L-1, TAN 0.21 mg L-1, alkalinity 136 mg L-1, pH 8.01, TSS 450 mg L-1, orthophosphate 1.2 ± 0.08 mg L-1, nitrite 0.12 mg L-1 and nitrate 41.7 mg L-1, indicating that the process of nitrification had occurred.

The results of the trial indicated that the C:N of 8.9 with inoculation of water from a mature tank is enough to maintain the water quality and shrimp growth performance.