An Experimental Brackish Aquaponic System Using Juvenile Gilthead Sea Bream (Sparus aurata) and Rock Samphire (Crithmum maritimum)

Ciliate diversity and growth rates in experimental recirculating aquaculture and aquaponics systems using microscopy

The function of recirculating aquaculture systems (RAS) relies on microbial communities, which convert toxic, fish-excreted ammonia into substances that can provide nutrients to plants as in the case of aquaponics systems. In the present study, heterotrophic protist communities of experimental sea water RAS and freshwater aquaponics systems were investigated using microscopy to characterize their diversity, natural abundance, and potential growth rates. Heterotrophic protist abundance was low (732 ± 21 to 5451 ± 118 ciliates L-1 and 58 ± 8 to 147 ± 18 nanoflagellates mL-1 in the aquaponics system and 78 ± 28 to 203 ± 48 ciliates L-1 in the RAS), which is in line with values typically reported for rivers. In the aquaponics system, ciliates grew faster in the fish rearing tanks (1.9 ± 0.01 to 1.21 ± 0.03 d-1 compared to 0.54 ± 0.03 to 0.79 ± 0.05 d-1 in the other compartments), while heterotrophic nanoflagellates grew slower in drain tanks downstream of the hydroponics compartment (0.5 ± 0.3 to 1.37 ± 0.05 d-1 and 4.09 ± 0.11 d-1 to 6.03 ± 0.34 d-1in the other compartments). Results indicated distinct niches and reduced microeukaryotic diversity at the end of the system's operation cycle.

Harnessing the Value of Tripolium pannonicum and Crithmum maritimum Halophyte Biomass through Integrated Green Biorefinery

Bioactive extracts are often the target fractions in bioprospecting, and halophyte plants could provide a potential source of feedstock for high-value applications as a part of integrated biorefineries. Tripolium pannonicum (Jacq.) Dobrocz. (sea aster) and Crithmum maritimum L. (sea fennel) are edible plants suggested for biosaline halophyte-based agriculture. After food production and harvesting of fresh leaves for food, the inedible plant fractions could be utilized to produce extracts rich in bioactive phytochemicals to maximize feedstock application and increase the economic feasibility of biomass processing to bioenergy. This study analyzed fresh juice and extracts from screw-pressed sea aster and sea fennel for their different phenolic compounds and pigment concentrations. Antioxidant and enzyme inhibition activities were also tested in vitro. Extracts from sea aster and sea fennel had phenolic contents up to 45.2 mgGAE/gDM and 64.7 mgGAE/gDM, respectively, and exhibited >70% antioxidant activity in several assays. Ethanol extracts also showed >70% inhibition activity against acetylcholinesterase and >50% inhibition of tyrosinase and α-glucosidase. Therefore, these species can be seen as potential feedstocks for further investigations.

Freshwater-adapted sea bass Dicentrarchus labrax feeding frequency impact in a lettuce Lactuca sativa aquaponics system

The aim of this study is to investigate the effect of three daily fish feeding frequencies, two, four and eight times per day (FF2, FF4, and FF8, respectively) on growth performance of sea bass (Dicentrarchus labrax)and lettuce plants (Lactuca sativa) reared in aquaponics. 171 juvenile sea bass with an average body weight of 6.80 ± 0.095 g were used, together with 24 lettuce plants with an average initial height of 11.78 ± 0.074 cm over a 45-day trial period. FF2 fish group showed a significantly lower final weight, weight gain and specific growth rate than the FF4 and FF8 groups. Voluntary feed intake was similar for all the three feeding frequencies treatmens (p > 0.05). No plant mortality was observed during the 45-day study period. All three aquaponic systems resulted in a similar leaf fresh weight and fresh and dry aerial biomass. The results of the present study showed that the FF4 or FF8 feeding frequency contributes to the more efficient utilization of nutrients for better growth of sea bass adapted to fresh water while successfully supporting plant growth to a marketable biomass.