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The aquaculture industry plays a key role in world food security and the effluents from these production systems are rich in nutrients that have not been incorporated into biomass of fed species being farmed (these nutrients are present in the form of uneaten feed, faeces and other excretion products). Integrated multi-trophic aquaculture (IMTA) conceptualizes the recovery of these nutrients into valuable biomass of extractive species, with polychaetes and halophyte plants, respectively, being key species to recover nutrients present in the form of particulate organic matter (POM) and dissolved inorganic matter (DIM - includes dissolved inorganic nitrogen and phosphorus, DIN and DIP, respectively). This study aimed to evaluate the efficiency from integrating polychaete assisted sand filters (PASFs) and halophyte plants produced in aquaponics in the filtration of aquaculture effluents, being divided into 5 complementary studies. The first study aimed to evaluate the efficiency achieved with PASFs (using Hediste diversicolor) when under contrasting concentrations of unused nutrients present in the effluent water of a semi-intensive fish farming system (Sparus aurata) using earthen ponds. It was possible to conclude that the reproductive success of H. diversicolor was achieved only in the two PASFs receiving effluent water with a higher concentration of POM (1.5-1.8 mg Lˉ¹), with PASFs contributing to retain ≈ 70% of available POM. The larvae of polychaetes Diopatra neapolitana, Sabella cf. pavonina and Terebella lapidaria naturally colonized the PASFs employed in this study and adapted to IMTA culture conditions. The second study evaluated the valorisation, in terms of essential fatty acids (EFA), of the biomass of the four above-mentioned polychaete species. Their fatty acid (FA) profile revealed to be enriched with n-3 EFA, such as eicosapentaenoic and docosahexaenoic acids (≈ 1.5 - 4.8 and 1.0 - 1.1 μg mgˉ¹ DW, respectively). The FA profile of D. neapolitana, S. cf. pavonina and T. lapidaria was described for the first time in this study. The FA profiles of H. diversicolor and T. lapidaria revealed the highest level of similarity to that of aquafeed provided to fish farmed in this IMTA design. The third study aimed to optimize the timeframe to produce a premium biomass of H. diversicolor enriched with EFA when supplied a commercial aquafeed (during 10, 20 and 40 days) and grown under different combinations of temperature (20 and 25 ºC) and salinity (15, 20 and 25). Here, the different culture conditions did not contribute to significantly modify the FA profile of H. diversicolor. Total FA concentration (70 - 90 μg mgˉ¹ DW) and n-3 and n-6 FA concentration (17-19 and 13-17 μg mgˉ¹ DW, respectively) incremented progressively, and no plateau was achieved. At the end of the study period, polychaetes exhibited a FA profile with greatest similarity to the one displayed by the aquafeeds than to the ones exhibited by initially stocked/wild polychaetes. It was also possible to report evidence of de novo FA biosynthesis (e.g., 20:3 n-6, 20:3 n-3, 20:4 n-3). The fourth study evaluated the efficiency of different IMTA configurations (1 single polyculture tank with 0.3 m² [1T] or 2 tanks to separate trophic levels with 0.6 m² [2T]) of combined culture of PASFs (using H. diversicolor or Arenicola marina) and halophyte plants produced in aquaponics (Salicornia ramosissima) using effluent water of a facility performing zootechnical trials using shrimp (Litopenaeus vannamei).It was concluded that extractive species when cultured in 1T design exhibited similar bioremediation values than those achieved under 2T design (reduction of 74-87% POM, 56-64% DIN and 60-65% of DIP). Considerable productivities were obtained for the polychaete H. diversicolor (≈5,000 ind. m ˉ²; 78-98 g m ˉ²), while A. marina failed to adapt to culture conditions and exhibited a low survival ( |
