Salinity affects the efficiency of a brackish aquaponics system of sea bass (Dicentrarchus labrax) and rock samphire (Crithmum maritimum)

Brackish aquaponics using euryhaline fish and halophyte plants may be a sustainable method of functional food production. In addition, they could have a great potential as high nutritional, commercial and pharmaceutical value. This study investigated the effect of three different salinity levels (8 ppt, 14 ppt and 20 ppt) on the growth performance of sea bass (Dicentrarchus labrax) and rock samphire (Crithmum maritimum), the first-time produc-tion of essential oil and the nutrient-removal efficiency of rock samphire in a brackish aquaponic system. A total of 135 sea bass (weight 8.2 +/- 0.15 g, length 9.5 +/- 0.33 cm) and 54 rock samphire individuals (height 7.7 +/- 0.20 cm) were distributed in the nine aquaponics systems (rearing temperature 20 +/- 0.2 omicron C). The seabass growth performance was significantly higher (p < 0.05) at 8 and 14 ppt salinity group than in 20 ppt, and FCR was significantly better at 8 and 14 ppt than in the 20 ppt (p < 0.05) salinity group. Rock samphire at 8 ppt showed significantly better growth and survival than those at 20 ppt (p < 0.05). Nitrate and phosphorous removal ef-ficiencies were significantly higher at 8 and 14 ppt than at 20 ppt. Heat shock proteins (HSPs) and mitogen-activated protein kinases (MAPK) were differentially expressed, showing tissue-specific responses. The highest yield of essential oils was obtained at a salinity of 14 ppt (0.31 +/- 0.03 mL per 100 g of dry plant weight). Seabass and rock samphire can have satisfactory growth performance in a tailored-made brackish aquaponic system and under the frame of sustainability and usage of saline water.

Automated summary

Brackish aquaponics using euryhaline fish and halophyte plants have potential as sustainable method for functional food production and high nutritional, commercial, and pharmaceutical value. The study found that sea bass exhibited better growth performance and feed conversion rate at 8 ppt and 14 ppt salinity levels compared to 20 ppt, while rock samphire showed better growth and survival at 8 ppt. Nitrate and phosphorous removal efficiency were higher at 8 ppt and 14 ppt, and essential oil yield of rock samphire was highest at 14 ppt. Overall, this research demonstrates the satisfactory growth performance of sea bass and rock samphire in a tailored brackish aquaponic system.