Sustainable Marine Aquaponics: Effects of Shrimp to Plant Ratios and C/N Ratios

Integrated aquaponic food production systems are capable of producing more food on less land using less water than conventional food systems, and marine systems offer the potential of conserving freshwater resources. However, there have been few evaluations of species combinations or operational parameters in marine aquaponics. The goal of this experiment was evaluation of stocking density ratio of Pacific whiteleg shrimp (Litopenaeus vannamei) to three edible halophytes (Atriplex hortensis, Salsola komarovii, and Plantago coronopus) with two C/N ratios in a 3 × 2 factorial design. There were three stocking density ratios (shrimp: plant), 2:1, 3:1, and 5:1; and two C/N ratios, 12 and 15. The results indicated that stocking density ratio exerted a significant impact on shrimp growth. Shrimp reared in 2:1 and 3:1 treatments had better growth performance. In contrast, plants were affected by both stocking density ratio and C/N ratio. Halophytes grown in stocking density ratios of 3:1 and 5:1 with a C/N ratio of 15 had better growth performance and nutrient content. The concentrations of TAN and NO2– were below 0.2 mg/L throughout the experiment, including the higher stocking density ratio treatments. In conclusion, the stocking density ratio of 3:1 with a C/N ratio of 15 was suggested as the optimal condition for the operation of marine aquaponics in which whiteleg shrimp and the three halophytes are target crops.

Physiological Adaptation to Water Salinity in Six Wild Halophytes Suitable for Mediterranean Agriculture

Owing to the high interspecific biodiversity, halophytes have been regarded as a tool for understanding salt tolerance mechanisms in plants in view of their adaptation to climate change. The present study addressed the physiological response to salinity of six halophyte species common in the Mediterranean area: Artemisia absinthium, Artemisia vulgaris, Atriplex halimus, Chenopodium album, Salsola komarovii, and Sanguisorba minor. A 161-day pot experiment was conducted, watering the plants with solutions at increasing NaCl concentration (control, 100, 200, 300 and 600 mM). Fresh weight (FW), leaf stomatal conductance (GS), relative water content (RWC) and water potential (WP) were measured. A principal component analysis (PCA) was used to describe the relationships involving the variables that accounted for data variance. A. halimus was shown to be the species most resilient to salinity, being able to maintain FW up to 300 mM, and RWC and WP up to 600 mM; it was followed by C. album. Compared to them, A. vulgaris and S. komarovii showed intermediate performances, achieving the highest FW (A. vulgaris) and GS (S. komarovii) under salinity. Lastly, S. minor and A. absinthium exhibited the most severe effects with a steep drop in GS and RWC. Lower WP values appeared to be associated with best halophyte performances under the highest salinity levels, i.e., 300 and 600 mM NaCl.

Evaluation of Pacific Whiteleg Shrimp and Three Halophytic Plants in Marine Aquaponic Systems under Three Salinities

The effect of salinity on the growth performance of whiteleg shrimp (Litopenaeus vannamei) and three halophyte plants, red orache (Atriplex hortensis), okahijiki (Salsola komarovii), and minutina (Plantago coronopus), in a marine aquaponic system with biofloc was evaluated in this study. The experiment was conducted for 4 weeks, and the three treatments were 10, 15, or 20 ppt (parts per thousand). The growth performance of the shrimp and the three halophytes were affected by the salinity. Compared to the shrimp reared in 10 ppt, those reared in 15 and 20 ppt had higher final weight, weight gain rate (WGR), and specific growth rate (SGR), and lower feed conversion ratio (FCR). The results from shrimp raised in 15 ppt were 2.0 ± 0.1 g, 89.9 ± 2.2%, 2.3 ± 0.0%, and 1.5 ± 0.0, respectively, and those in 20 ppt were 2.0 ± 0.1 g, 93.9 ± 5.4%, 2.4 ± 0.1%, and 1.4 ± 0.1, respectively. On the other hand, the growth performance and nutrient content in halophyte plants decreased with the increasing salinity. In general, the three halophyte plants had better results in the 10 and 15 ppt treatments than those in 20 ppt. Therefore, the salinity of 15 ppt was suggested as the optimal condition for the integrated cultivation of whiteleg shrimp and the three halophytes in marine aquaponics. Additionally, they are compatible species for the development of marine aquaponics.