EFFECT OF GROWING SEASON ON THE COMMERCIAL YIELD OF THE NILE TILAPIA Oreochromis niloticus UNDER OUTDOOR BIOFLOC AND GREEN WATER TECHNOLOGY
The need to find sustainable aquaculture alternatives that improve the profitability of Nile tilapia Oreochromis niloticus has become a priority issue in the world and in southeastern Mexico, mainly due to the increase of commercial farms and unsatisfied demand. This study aims to compare the performance of Nile tilapia in two growth technologies: biofloc (BFT) and green water (GWT); and determine, based on bioeconomic indicators, the optimal production technology to two climatic season dry-rainy season (DR) and rainy-north season (RN). The experiment was performed in Motul, Yucatán, México.
The fish were reared in 6 geomembrane circular outdoor tanks (113 m3) at the same stocking density (42 fish/m3). The first batch (35.73 ± 4.85 g) was sowed in BFT and GWT on July 2017, which corresponded to rainy season, and the second batch (28.49 ± 77.49 g) on April 2018 or dry season. The fish were grown up to the market target weight of 450 ± 50 g. The concentration of dissolved oxygen was increased using a 2-HP injection aerator for each tank. The aeration of BFT tanks was complemented using 5.5-HP blower with 20 diffuser discs. Partial water replacements were made in the GWT tank, to keep the ammonium concentration low. BFT tanks were handled with zero water replacement. The BFT tanks were maintained with a C: N ratio of 10: 1 by the addition of molasses (30% C). The food ration was reduced daily by 25% from the fifth week of growth, and by 30% from the 12th week until the harvest. Fish growth and survival were not affected by the growth technology, but by the growing season (Table 1). The floc, total carbon and temperature in the BFT tanks were the parameters that significantly influenced the growth of the fish. Temperature, OD and microalgae influenced the growth of fish in GWT. The DR-BFT fish reached the target weight 28 days after DR-GWT, so finally the total feed consumption was only 3% lower than that of the GWT fish. DR-BFT had the lowest AGR, thus generating a final biomass of 15.05 kg / m3 and FCR 1.67; which represented 2.15 kg / m3 less than DR-GWT. The best performance was obtained in RN-GWT; the fish of this treatment reached the highest biomass (1962.8 kg) with a lower FCR (1.27) in the minimum harvest time (145 days).
