Efeito da adição de Chlorella vulgaris e melaço na qualidade da água e crescimento de alevinos de tilápia do nilo (Oreochromis niloticus) em sistema de bioflocos com baixa salinidade

Abstract

Among the production systems in aquaculture, the intensive system with bioflocs has been highlighting. Considering the great potential of this system for the cultivation of tilapia, the objective of this work was to evaluate the effect of the addition of microalgae (Chlorella vulgaris) and molasses quantity on the water quality, zootechnical performance, centesimal composition and hematological profile of Nile tilapia fingerlings grown in low salinity (10 g L-1). Fingerlings of Oreochromis niloticus with an average weight of 3.15 ± 0.5g were used, they were distributed in 12 rectangular boxes with an usable volume of 50 liters (0.05 m3) at a density of 680 fish m-3, in a factorial design (addition of microalgae and amount of molasses), making four treatments, being: two of them with molasses in the amount of 30% of the feed offered, BFT-30 (without C. vulgaris) and BFT-C30 (with C. vulgaris), and two with molasses in the amount of 50% of the feed offered, BFT-50 (without C. vulgaris) and BFT-C50 (with C. vulgaris), with three replicates each. The study lasted 70 days, during which time the molasses were added daily and the microalga was inoculated every five days to leave the experimental units in the concentration of 5x104 cell mL-1. At the end, the final weight, final length, specific growth rate, survival, feed conversion factor, protein efficiency rate, water consumption, sedimentation use and hematological profile showed significant differences (p≤0.05) when the effect of the amount of molasses addition was evaluated, as well as the combination of factors. The effect of the level of molasses addition was significant for most variables, while the addition of microalga was significant only for water consumption, planktonic community and mean corpuscular volume. The treatments with lower molasses addition (30%) presented better results, due to the fact that in the treatments with more molasses addition (BFT-50 and BFTC50) higher values of sedimentable solids were found (>50 mL L-1), which probably affected negatively the zootechnical performance of the animals. Therefore, the use of culture systems with bioflocs is a good option for production of Nile tilapia fingerlings, however, it is suggested a low rate of molasses addition in the culture system.