Different fertilizations will favor the predominance of different groups of bacteria in the biofloc system , and can affects the cost , management and the performance of the organisms. The aim of this work is to evaluate the growth of the macroalga Ulva lactuca when cultivated in an integrated system with shrimp Penaeus vannamei and fish Oreochromis niloticus using a chemoautotrophic system and a mixed system.
The experiment was carried out in an agricultural greenhouse with constant aeration and lasted 56 days . Two treatments was used with three replicates each : Chemoautotrophic system: system with prior fertilization (35 days before stocking the animals ) with ammonium chloride and sodium nitrite to reach a concentration of 1 mg L- 1 in the water ; and Mixed system: use of an inoculum (40%) of biofloc from an growout shrimp farm. Each treatment had three systems, each consisting of a 4 m3 tank where the shrimp were kept (350 shrimp m-2 ). The water circulated by gravity to a 0.7 m3 tank with fish (7 fish m-3 ). T he water from the fish tank was pumped into the 0.35 m3 macroalgae tank (0.1 g m-3 ) and returned by gravity to the shrimp tanks . The macroalgae was kept inside the tank using a circular structure with a diameter of 0.60 m near the surface . The initial weight of the macroalgae was 502.7 ± 0.50 g, and every 20 days the macroalgae were removed from the tank and weighed . The biomass produced was removed and the initial weight of the macroalgae was maintained . Nutrient and solids analyses were carried out twice a week .
There was no significant difference (p ≥ 0.05) between the treatments in the average biomass gain (Table 1). However, there was greater specific growth of the macroalgae on day 56 in the Chemoautotrophic treatment compared to the Mixed system. Significant differences were found between treatments in ammonia , nitrite and total suspended solids (TSS).
The reuse of water from an shrimp cultivation provided greater stability , showing low concentrations of ammonia and nitrite , similar to that found by Ferreira et al (2021) . The greater growth of the macroalgae in the last weighing in the chemoautotrophic system may be due to a lower concentration of total suspended solids , allowing more light to enter (Carvalho et al. 2023).
Growing the macroalgae in a mixed system proved to be viable due to its biomass production over the course of cultivation and greater control of nitrogen . In addition to being a system that reuses water from an existing crop , it is also more economical and sustainable.