Fertilizing synbiotic system with different vegetable brans: effects on nitrification, plankton composition, and growth of Penaeus vannamei in the nursery phase

Abstract

The aim of this study was to evaluate the effect of using different vegetable brans as organic carbon source in synbiotic system fertilization on the nitrification process, plankton composition, and growth of Penaeus vannamei in the nursery phase, also comparing it with the biofloc system. An extended nursery rearing was carried out for 53 days, at a density of 2000 shrimp m⁻³ (initial weight: 0.03 ± 0.01 g). The following treatments were established, with five repetitions: CW, clear water (control); BFT, biofloc system; RB, synbiotic system fertilized with rice bran; SB, synbiotic system fertilized with soybean bran; and WB, synbiotic system fertilized with wheat bran. The synbiotic fertilization protocol used a commercial blend of Bacillus subtilis and Bacillus licheniformis, molasses, sodium bicarbonate as buffer, and water. The fertilizers were processed by an anaerobic (24 h) and an aerobic (24 h) phase. BFT treatment used molasses as organic carbon source. At the end of the trial, final weight was higher in CW, BFT, and RB treatments than in WB. In RB, SB, and WB treatments, TAN was controlled between days 10 and 14 and NO₂⁻-N was controlled from day 40 of the trial, resembling a newly started system. At the end of the trial, a higher abundance of coccoid and bacillus was observed in the RB treatment, while a higher abundance of vibrio bacteria was observed in WB. Rice bran proved to be the best alternative for the synbiotic fertilization, as it presented a final weight (3.27 g) similar to BFT and CW treatments, and higher than WB (2.61 g). Also, the use of rice bran produced a high load of microorganisms, which can improve shrimp growth.