Níveis de proteína bruta em dietas para a tilápia do Nilo (Oreochromis niloticus) cultivada em sistema de bioflocos em duas fases de crescimento

One of the main mechanisms to improve water quality in aquaculture is through successive changes of water. The current situation does not allow the irrational use of water resources, because culture is facing restriction and water scarcity, that tendency to efficient and sustainable systems. In this context, the biofloc system has emerged as a promising alternative for aquaculture as water exchange is minimal or zero. The accumulation of organic matter, feces and nutrients, supplemental with carbon sources when necessary, combined with constant aeration of the water column, promotes the growth of ammonia nitrogen assimilators heterotrophic microorganisms. These serve as additional food for filter feeding fish such as Nile tilapia. Nutrition is the highest cost of production of fish chain. For decreasing of the crude protein content in rations were performeds two simultaneous experiments with Nile tilapia (Oreochromis niloticus) the average of initial weight was of 9.94 for first experiment and 47.75g for second experiment. These were conducted over a period of 61 and 98 days, respectively. five levels of crude protein were tested (17, 21, 25, 29 and 33% CP) and 3300 kcal of gross energy. Data were subjected to analysis of variance and polynomial regression (p<0.05). The water quality parameters were affected by the CP levels in the diet, except for temperature and nitrite. Regarding the performance, there was a linear increase in the final weight and average daily gain and reduced feed conversion with increasing CP levels in the first experiment, The optimal level of PB was close to 33% for tilapia juveniles up to 56g. In the second experiment was a quadratic effect with maximum inclusion level of 26.02% and 27.31% CP obtained these for feed conversion and average daily gain. The fish fed with lower protein levels had increased deposition of fat in the carcass due to higher energy: protein ratio, and excess PB in the second experiment was used to produce lipids. The low nutritional value of floc was probably affected by excess of solids, this may have compromised its contribution as a source of food for tilapia juveniles. However, it is possible to say that tilapia from 10 to 56g can be fed with 33% and 56 to 230g with 26-28% CP in biofloc system.