5 mg L-1 , temperature remained around 29 °C, and salinity was maintained at 20 g L-1 . All water quality and shrimp performance parameters were unaffected (p > 0.05), but fish fed with 3% of body weight day-1 exhibited higher values for all growth performance parameters (p < 0.05) , excluding survival (p > 0.05) (Table 1). Macroalgae growth was affected (p < 0.05) , showing lower values in the treatment with the highest feeding rate. Total sludge produced in the highest feeding rate treatment was higher than that in the lowest (p < 0.05) , but it did not result in higher sludge produced per organism biomass (p > 0.05). Increasing the fish feeding rate favored the final biomass and yield of the multitrophic system and did not affect the system conversion , generating an economic gain.
The integrated multitrophic aquaculture can reduce the surpluses of solids and inorganic nutrients that tend to increase over time in a shrimp biofloc system, since the model integrates organisms from different trophic levels, all sharing the same production system and, consequently, the nutrients. Tilapia and macroalgae play an essential role in this system due to the ability to use flocs as a feed source and uptake inorganic nutrients, respectively. This study evaluated the effect of two feeding rates (1 and 3% of body weight day-1) of tilapia Oreochromis niloticus, as an organic consumer , integrated with shrimp Penaeus vannamei as the main species and macroalgae Ulva lactuca as an inorganic consumer in a biofloc system regarding water quality, sludge produced, and performance of the organisms and system. The study was carried out for 52 days in a greenhouse at the Marine Aquaculture Station - FURG . The study consisted of an experiment with two treatments and three replicates each: 1) 1 % body weight day-1 and 2) 3% body weight day-1. Shrimp (4.28 ± 0.12), fish (16.98 ± 0.92), and macroalgae were stocked in 14, 4, and 4 m3 tanks of useful volume, respectively, at a density of 230 shrimp m-2, 30 fish m-3, and 0.13 kg of macroalgae m-3 (considering the total volume of the system). Macroalgae were placed in a shallow float within 10 cm from the surface . The system remained in constant recirculation whereby water circulated from shrimp tank to fish tank through a submerged pump . Then, by gravity, water flowed to macroalgae tank and returned to shrimp tank. Dissolved oxygen levels were main tained above