Effect of the reuse of the production medium on the rearing of tilapia Oreochromis niloticus(Linnaeus 1758), in a superintensive system with bioflocs
The growth of aquaculture production is fundamental to supply the increase in world demand for fish, with the tilapia Oreochromis niloticus being one of the main species of fish that leverage this activity. However, this intensification of aquaculture causes environmental impacts and attacks the principles of sustainability, making it necessary to search for more sustainable means of production. Among the alternatives, the biofloc technology (Bioflocs Tecnology - BFT) is currently considered one of the most environmentally friendly, mainly because it reduces the use of water and recycles the nutrients inserted in the system. However, it still presents some problems in relation to the discharge of effluents and the accumulation of nutrients in the environment.Thus, the possibility of reusing the production medium in subsequent cycles becomes essential to increase the sustainability of biofloc technology. This work aimed to evaluate different percentage levels of reuse of the production medium (effluent) in the O. niloticus rearing in BFT system. The experiment lasted 40 days and was carried out in a closed environment in twelve tanks of 1000L and useful volume of 400L, with four treatments in triplicate, one control without reuse (0% - T0) and three percentage levels of reuse of the effluent: (25% -T25, 50% - T50 and 100% - T100). The fry (3.79 ± 0.12g) were stored at a density of 500 individuals/m3. Temperature, dissolved oxygen pH, ammonia, nitrite, nitrate, phosphate, suspended solids and alkalinity were monitored.The material for evaluation of the microbial community present in the production medium was collected every 3 days. Organic fertilization was performed using molasses as a carbon source to maintain the ideal C/N ratio for the development of the microbial community that controls changes in the ammonia concentrations in the system. Biometrics were performed every ten days to evaluate the growth of the fish and histological analysis of the gills every fifteen days. The water quality parameters remained within the acceptable range for the species in all treatments with water reuse, except for the treatment without water reuse (T0), which presented higher concentrations of ammonia and nitrite, which resulted in greater damage in the gills and worse zootechnical performance of the animals in relation to the other treatments.The results of the present study suggest that it is feasible to reuse 100% of the production medium in a subsequent cycle for Nile tilapia.