The growing demand for fish products and the dwindling productivity of marine fish stocks due to the overexploitation of fisheries place the aquaculture industry as a key contributor to the global fish supply. The intensive development of aquaculture has raised a range of environmental concerns such as effluent discharge, excessive use of resources and dependence on commercial feed. In this context, the development of sustainable aquaculture systems is becoming the cornerstone for long-term aquaculture expansion, and to achieve environmental sustainability. Integrated multitrophic aquaculture (IMTA) is regarded as a suitable approach to limit aquaculture nutrients and organic matter outputs through biomitigation. The cocultured species are used as biofilters, and each level has its own independent commercial value, providing both economic and environmental sustainability. Here, environmental issues of aquaculture and the current status of IMTA are reviewed and its future prospects discussed. Also, the opportunities to expand this systems' complexity with increased added-value and trophic levels are introduced.

In land-based pond cultures, periphyton is considered to be a complementary food source for cultured fish. In cage aquaculture, studies on the use of periphyton are scarce and do not support the viability of periphyton-based cage culture. The aim of this study was to evaluate the potential of periphyton-based cage culture of Nile tilapia in a hydroelectric reservoir in Brazil at three stocking densities and two feeding regimes.Sex-reversed male Nile tilapia Oreochromis niloticus (46.56±2.53 g) were placed in 21 cages (6 m 3 -2 x 2 x 1.5 m each) with or without bamboo substrates for periphyton growth. A completely randomized design with three replicates per treatment was used to test the effect of substrate inclusion in the three stocking densities (80, 60, 40 kg of fish/m 3 ) associated with two feeding regimes (100% and 50% of daily ration). Three cages without bamboo substrates were included in the experimental design as control group (CTRL) (80 kg/m 3 and 100% of daily ration). The study demonstrates the efficiency of using substrates for Nile tilapia in cages in the reservoir. The presence of bamboo substrates improved the weight gain of fish but reduced the carrying capacity of the cage at the highest density. The concentration of dissolved oxygen in the cages was improved by the presence of substrate between 50 and 140 days of the trial and reduced after 155 days of culture. The inclusion of bamboo substrates inside the cages allows producing up to 52 kg/m3 of Nile tilapia using 32% less diet in a period almost 20% shorter than in the CTRL group. If farmers prefer to produce 80 kg/m3, they can use 30 % less diet but the production period would be 20% longer.

We evaluated the production costs and the profitability of using bamboo substrates to enhance periphyton production in cages, in combination with a restricted diet and reduced stocking densities. Nile tilapia (46.56 ± 2.53 g) were placed in 21 cages, and the inclusion of bamboo substrates was evaluated in three different stocking densities (40, 60, and 80 kg of fish/m 3) in association with two feeding schemes (100% and 50% of daily ration). No bamboo substrates were included in the control group. The inclusion of the bamboo substrates in cages increased fish weight gain, shortened the farming cycle length, and improved the feed conversion ratio. The proposed production model of Nile tilapia farming in cages with substrates offers a way for small-scale producers to increase the efficiency of the system with annual operating income up to 57% higher and the profitability index up to 87% higher than the currently used system adopted by Brazilian farmers.