The goal of this work was to evaluate the use of organic acid (Eurotec Nutrition, Brazil) in the water of biofloc technology to reared Nile tilapia (Oreochromis niloticus). The work was divided into two steps: 1st) in vitro assays, inhibition test and dose-response; and 2nd) in vivo assay with Nile tilapia juveniles in BFT.
For the in vitro assays, minimal inhibitory concentration (MIC) assays were performed against seven pathogenic bacteria (two Aeromonas hidrophyla, A. veronii, Staphylococcus aureus, Citrobacter freundii, Vibrio parahaemolyticus, and V. alginolyticus). For the dose-response test, 2.5 ppm, 5.0 ppm, 10.0 ppm and 20.0 ppm (doses defined from the product’s user manual) were evaluated in triplicate. Fifteen bottle units with a capacity of 1 liter were used, all bottles received a constant and independent aeration system, which entered through the lid. For in vivo assay, in experimental units (8 retangular tanks, 0.72 m² x 0.35 m) with 250 L, water fertilization was carried out with a carbon source (sugar) and powdered diet to keep the carbon:nitrogen (C:N) ratio 10:1, resulting in an initial solids concentration of 100.0 mg L-1. The experimental units were divided into two groups (organic acid and control) in quadruplicate, each tank with 20 fish. Fish were fed three times per day (8:00, 12:00 and 16:00), with commercial diet, with 3% of the fish biomass. Dissolved oxygen and temperature were performed measured twice a day. Total suspended solids (TSS), settleable solids, pH, hardness and alkalinity were monitored twice a week. Ammonia (total ammonia nitrogen − TAN), nitrite-N, and nitrate-N were also monitored twice a week. Growth performance was determined after six weeks.
Organic acid had an inhibitory effect against all pathogenic bacteria tested (Table 1). The largest inhibition halo (mm) was obtained against the bacterium S. aureus (60.00 ± 5.00), and the smallest halos were obtained against A. hidrophyla (42.00 ± 3.46) and C. freundii (41.00 ± 1.73). The 2.5 ppm dose presented the most interesting results for the in vivo assay, as it did not significantly reduce the pH and alkalinity of the water. Nile tilapia shown FCR closed 1.0 in both treatments, as well, SGR above 3.4%.day-1 acid reduced the nitrogen compounds orthophosphate, the other parameters did not diverge (Table 1).
The organic acid in the water in BFT, at a dosage of 2.5ppm, proved to be favorable against the reduction of toxic ammonia, nitrite and orthophosphate, improving the Nile tilapia culture environment.