No abstract

Protein‐dependent aquaculture generates large amounts of nutrient‐rich residuals; a feasible way to develop sustainable production systems is to integrate Decoupled Aquaponic Systems (DAPS) with residual water bioprocesses, to combine Photoautotrophic Biofloc Technology (P‐BFT) aquaculture and hydroponic horticulture. This study describes the characteristics of residual water from Oreochromis niloticus aquaculture performed with P‐BFT inoculated with Chlorella microalgae, reared during the nursery (180 fish m3) and grow‐out (55 fish m3) phases. The experiment included five treatments: photoautotrophic BFT inoculated with Chlorella sp. (M), C. sorokiniana 2714 (CV), and C. sorokiniana 2805 (CS), and chemoautotrophic (Q) and heterotrophic (H) as controls. Elemental characteristics in liquid and solid residual fractions (15 macro‐ and micronutrients) were compared among treatments and against Hoagland & Arnon solution with hydroponics and used in Nutrient Film Technique (NFT) hydroponic horticulture including five plant species: lettuce (Lactuca sativa), pak‐choi (Brassica rapa subsp. chinensis), rocket (Eruca sativa), spinach (Spinacia oleracea) and basil (Ocimum basilicum). The physicochemical parameters were ideal for O. niloticus and plants. The relationship between N:P was ideal until weeks 16–22 in the photoautotrophic treatments, compared with hydroponic solutions. Micronutrient content was greater in the solid than a liquid fraction. The best BFT effluent regarding fish and plant growth was photoautotrophic treatments. Oreochromis niloticus BFT aquaculture in photoautotrophic mode using microalgae Chlorella inoculations provided residual water beneficial to hydroponic horticulture in DAPS located in coastal arid zones where freshwater is scarce, improving aquaculture performance and reusing water and nutrients.

Salicornia bigelovii Torr. is a potential new crop for coastal and saline lands, because of the oil content of its seeds, its properties as fresh vegetable, forage, and other uses. As a true halophyte, it can grow with seawater irrigation. The aim of this study was to determine the phenology and water requirements of Salicornia as a new plant resource in growing areas for salt-tolerant crops in coastal and saline lands, and elucidate scenarios of sustainability about these issues. Water requirements were estimated in experimental plots on the coastal line and fulfilled with drip irrigation connected to seawater aquaculture discharge ponds, 30 m from the sea. The recorded phenological events were germination, flowering, fructification, maturation, and physiological death. Results reflect the difficulty to adopt it as a new crop because of its long-life cycle, around nine months, contrasting with the life cycle of common crops, from three to four months. Irrigation needs reached a depth of 240 cm, significantly exceeding those of conventional crops. Such limitations are highlighted, but also its potential use as a biofilter of coastal aquaculture effluents, being a productive target-biomass, feasible to be used as a dual-purpose use of water and energy required in aquaculture farms.

Low nutrient and high pH of circulating water represent two of the main issues to overcome for a successful combination of aquaculture and hydroponics in aquaponics offering a sustainable and circular economy solution for vegetable production. The purpose of this study was to screen the tolerance of four herbs to high pH and low nutrient concentration in hydroponics, i.e., green and red basils, mint, and rocket salad, with a focus on plant yield and nutraceutical aspects. Results highlighted green basil as the most tolerant species to low nutrient and high pH conditions followed by mint. On the contrary, negative effects from high pH and low nutrient were reported on red basil and especially rocket salad, which strongly affect their marketability parameters. Rocket salad fresh biomass was more than halved under the combination of high pH and low nutrients. Results on green and red basil showed the importance of testing the tolerance to these agronomic conditions at both species and variety levels. Despite the reduction in biomass, leaf pigments were not influenced by high pH and low nutrients and therefore can be considered parameters of minor importance for the evaluation of these species. In conclusion, the tolerance of green basil and mint to high pH and low nutrients under hydroponic conditions has been highlighted. Further investigation coupled with fish farming will be able to reinforce the convenience of using these species for aquaponics.

Recirculating aquaculture systems (RASs) are an efficient method for developing sustainable aquaculture and the development of a feed strategy for RASs could be a key factor for the success of culturing Oreochromis niloticus. The daily protein intake (DPI) mathematical function related to body weight (BW) was designed (DPI = −3.818 ln (BW) + 30.158) named DPI 1.0 = 100%. Three feeding rates were established, DPI 1.4, 1.2 and 1.0, and were implemented in an RAS production cycle (100 fish/m3) for 34 weeks. The final growth measurements were 908.0 ± 57.9 g (DPI 1.4), 887.0 ± 113.5 g (DPI 1.2) and 702.2 ± 38.1 g (DPI 1.0) (p < .05), with feed conversion rates (FCRs) of 2.3, 1.9 and 1.9, respectively; the survival was ≥ 98.3% (p > .05) for all treatments. DPI levels conditioned the growth of the fish and the proportion of lipid: protein in the bodies of O. niloticus but not in the fillets. The mathematical function DPI 1.2 = 120% (DPI = −4.582 ln (BW) + 36.19) used in the RAS at the 40% protein level improved fish growth, the protein efficiency ratio and FCRs. The DPI values were estimated for 49 different cases and feeding strategies showed lower values than most of the different DPI mathematical functions used and cited in this work. Therefore, DPI metric is a good tool that provides the specific requirements of protein for O. niloticus growth, which can enable farmers to ration feed and improve energy use (kWh/fish) and facilitate the integration of RAS with horticulture.