Food management of Litopenaeus vannamei grown in a biofloc system: effects of food restriction and different feeding rates on zootechnical parameters
Artificial food is a major expense in intensive shrimp farming around the world. In biofloc system cultivation, the microbial community can be an additional source of food, leading to a possible reduction in the amounts of feed to be added to the system. However, it is not known for sure how much feed can be saved and whether the use of different feeding management techniques can contribute to an even greater reduction in the amounts of feed to be offered to cultivated animals. Thus,four experiments were designed using different feeding rates and different feeding management techniques in order to see if bioflocs can contribute to the reduction of feeding rates and how food restriction can influence the growth and survival parameters of Litopenaeus vannamei grown in biofloc system. Feed rates for all experiments were calculated considering an expected weekly growth of 1 g / week and an estimated mortality of 0.5% / week. In experiments 1, 2 and 4, each treatment corresponded to a different feeding rate and each of these rates corresponded to a fixed feed conversion rate. In the third chapter the feed rate was calculated using a fixed feed conversion rate of 1.45.The experiments were carried out in 150 L tanks, with stocking densities between 300 and 400 shrimp / m3. The first experiment aimed to evaluate the use of different feeding rates during a 60-day cultivation cycle of L. vannamei in a biofloc system. The tested treatments were: T0 (without addition of feed), T0.4, T0.8, T1.2, T1.6 and T2.0. The final weight (g) was lower at T0 (P <0.05), followed by T0.4, T0.8 and T1.2 (P <0.05), with no differences between T1.6 and T2.0 (P> 0.05 ). The treatment without added feed showed the lowest survival (P <0.05) and all other treatments had survival rates above 80%, with no statistical differences between them (P> 0.05). Shrimps can survive for long periods in the biofloc system with a reduced amount of artificial food (T0.4).As there were no differences between T1.6 and T2.0, it can be concluded that there is no need to increase feed rates at this level in biofloc cultivation, saving about 25% of the total feed to be added. The second study aimed to analyze the effects of different feeding rates and subsequent re-feeding on the cultivation of shrimp using the BFT system. The first phase of the study (food restriction) lasted 21 days, and the following treatments were tested: T0 (without addition of feed), T0.3, T0.6, T0.9, T1.2, T1.5, T1. 8 and T2.1. In the second phase (feedback), feed rates were based on a fixed conversion rate of 1.45. At the end of food restriction, treatments T0, T0.3 and T0.6 had the lowest final weights (P <0.05). Survival was low only at T0 in both phases of the experiment.In the second phase, treatments T0, T0.3 and T0.6 showed partial compensatory growth. The study indicates that this management technique allows savings of up to 24.79% of the feed to be added to the crop. The third study evaluated different cyclical periods of fasting and refeeding. Five treatments were tested: Control, in which the animals were fed daily; F5S2, 5 days of feeding followed by 2 days without receiving feed, F3S4, 3 days of feeding followed by 4 days without receiving feed, and F5S2-R and F3S4-R in which the feeding days were the same mentioned above, however with reduction of food quantities according to the days on which they were fed. At the end of the study, the shrimp from treatments F5S2 and F5S2-R did not show significant differences compared to the control for survival,final biomass, specific growth rate, feed conversion rate and productivity (P> 0.05) and indicate complete compensatory growth, justified by the increase in food consumption. The fourth experiment analyzed the use of biofilm to reduce feed rates. The tested treatments were: T0 and T0 + B (without addition of feed, with and without biofilm, respectively), T0.6 and T0.6 + B, T1.2 and T1.2 + B, T1.8 and T1. 8 + B. The study lasted 42 days. At the end of the experiment, the shrimp that were grown without added feed had the lowest final weights and survivals, regardless of the use of biofilm (P <0.05). The T1.2 + B treatment showed no significant differences between T1.2, T1.8 and T1.8 + B for growth and feeding parameters.The results allow us to conclude that the presence of biofilm in the T1.2 + B treatment represented savings of 35% of the total feed to be offered. According to the results obtained in this thesis, it can be concluded that the microbial community of the biofloc system can represent an important supplementary source of food, reducing operating costs and improving the sustainability of the cultivation system.