The present work aims to describe the nitrogen (N) budget in integrated aquaculture systems with Nile tilapia (Oreochromis niloticus) and Amazon River prawn (Macrobrachium amazonicum) in earthen ponds, with and without the addition of different substrates. The experimental design was completely randomized, with three treatments (without a substrate, with a geotextile fabric substrate, and with a bamboo substrate) and four replications. Diet was the major input of N in the systems, ranging from~65 to 71% and followed by inlet water (~26-31%). The portion retained in reared animals and periphyton ranged from~21 to 25% (being~21-24% in fish and prawns). The outputs that contributed most to the accumulation and release of N were, respectively, sediment (~24-38%) and N2 (~30-36%) emitted to the atmosphere. The addition of substrates did not improve the accumulation of nitrogen in the biomass of the target species. This suggests that the periphyton had a minor role on feed availability. In general, the systems were not efficient in using nitrogen since only~22% of all available nitrogen was retained into prawn and tilapia biomass. On the other hand, the emission of N 2 (an inert gas) to the atmosphere almost compensated the nitrogen supplied in the diet that was not assimilated by the reared animals and periphyton. In addition, data suggest that the integrated aquaculture in stagnant ponds may sequester substantial amounts of nitrogen from nutrient-rich aquatic environments and could be used as a mitigation tool.
Integrated multitrophic aquaculture (IMTA) systems are designed mainly for efficient use of resources. Substrates added to aquaculture ponds provide space for periphyton to settle and recover nutrients, making these nutrients available to the species being reared. The present study is centered on the phosphorus budget, analyzing the main ecological compartments of IMTA systems in earthen ponds stocked with Amazon River prawn, Macrobrachium amazonicum, and Nile tilapia, Oreochromis niloticus, with or without different added substrates. The experimental design was completely randomized, with three treatments (without a substrate, with a geotextile fabric substrate, and with a bamboo substrate) and four replications. Phosphorus entered the systems mainly in tilapia feed (ca. 50–61%), inlet water (ca. 17–27%), and fertilizer (ca. 6–7%). Input of phosphorus from other compartments ranged from 1.5 to 1.9%. Most phosphorus was accumulated at the pond bottom as sediment (ca. 60–68%) and fish biomass (ca. 18–26%), or discharged in the outlet water (ca. 7–10%). Feeding is the main driver for the distribution of phosphorus in the ponds. Levels of phosphorus retained in reared animals (20–28%) were higher in these IMTA systems than in tilapia and prawn monocultures (reported as 10–20% and 10–13%, respectively). Nonetheless, the present data showed that the addition of different types of substrates might not improve the recovery of phosphorus in animal biomass as initially supposed. Even so, these IMTA systems decreased the amount of phosphorus released in effluents, and this decrease was enhanced by the addition of substrates, reducing the impact on the receiving waterbodies.
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