Efeitos de diferentes fontes de carbono e relações C:N na qualidade da água e no desempenho de Oreochromis niloticus cultivada com tecnologia de biofloco

Abstract

The development of aquaculture systems based on biofloco technology can contribute to the fish production in regions with reduced water availability. Thus, this thesis evaluated the quality of water in the Nile tilapia culture, Oreochromis niloticus, as well as performance and animal welfare with biofloco technology in the in the nursery phase and growout, using different carbon sources and relations C:N. In the first study, It was adopted a experimental design, with two relationships carbon (C) and nitrogen (N) (10:1 and 20:1) and three carbon sources (molasses, sugar and cassava starch) in the nursery phase. The water quality was evaluated daily on the basis of temperature, dissolved oxygen, pH, redox potential, conductivity, transparency and salinity. It was monitored weekly up ammonia, nitrite, nitrate, phosphate, alkalinity, settleable solids, turbidity and total suspended solids. The best results in the induction of microbial flocs were observed with added molasses or sugar in the C:N ratios 10:1 and 20:1. Induction to heterotrophic means causes constant changes in water quality that can harm the growth and survival of tilapia fingerlings. The temperature (23.2 ± 0.8ºC), dissolved oxygen (7.1 ± 0.4 mg/L), pH (8.1 ± 0.1), the redox potential (168.2 ± 25.2 mV), conductivity (2.0 ± 0.1 mS/cm) and salinity (0.3 ± 0.8 ‰) did not differ significantly between treatments (P>0.05). The C:N ratio and carbon source influenced some variables, as alkalinity, settleable solids (SS), turbidity and total suspended solids (TSS) showing values significantly higher in the C:N ratio of 20:1 (P<0.05). In the second study, we evaluated the influence of molasses used different C:N ratios and different carbon sources on water quality, productive performance and health of tilapia grown with biofloco technology in the fattening stage. The average values of total plasma protein (5.9 g/dL), albumin (0.8 g/dL) and globulin (5.1 g/dL) demonstrating the potential of biofloco technology in development of the immune system fish. Were stocked 50 fingerlings/m3 (73.2 ± 2.7 g) in 12 tanks (800 L). After 107 days of cultured, it was possible to produce 14.5 ± 1.0 kg/m3 of survival over 95% with no significant differences among the treatments. In the third study, molasses can be used as a carbon source to achieve C:N 10 or 20:1 ratios on tilapia culture with biofloco technology. The animal performance and welfare of tilapia was satisfactory with all carbon sources proving to be effective in maintaining the physical and chemical parameters. The most rapid degradation of molasses and sugar may have provided higher levels of carbon as a substrate for the formation of microbial flocs. Information and knowledge of haematological variables and water quality in tilapia farming with biofloco technology can be used by the fish farmer as an evaluation tool of creation of system of ecological prudence and animal welfare.