Investigating Salinity Effects in Brackish Aquaponics Systems: Evidencing the Co-Cultivation of the Halophyte Crithmum maritimum with the Euryhaline Sparus aurata

The possibility of simultaneous production of halophyte and euryhaline fish creates huge interest in both commercial aquaponics systems and in research. The aim of the present study was to investigate the effect of three different salinities (8, 14, and 20 ppt) on the growth performance and survival rate of sea bream (Sparus aurata) and rock samphire (Crithmum maritimum) in an experimental brackish aquaponic system. Furthermore, induction of heat shock proteins (Hsps) and phosphorylation of mitogen-activated protein kinases (MAPKs) were assessed through the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analysis. A total number of 234 sea bream individuals were divided into nine autonomous aquaponic systems. The experiment lasted 45 days. In total, 54 individuals of rock samphire were used and were distributed into groups of six individuals per hydroponic tank using the raft method. Water quality showed stable fluctuation throughout the experiment, strongly supporting fish and plant growth performance and survival in both treatments. The results show that better growth performance for both sea bream and rock samphire (height increase) was evident in salinity 8 ppt compared to salinities 14 ppt and 20 ppt. Minimal or mild histopathological alterations were detected in gills, midgut, and liver for all three salinity groups. Exposure to different salinities modified Hsp60 and MAPKs expression in a tissue- and time-specific manner. During exposure to 8 ppt, constant Hsp60 levels and phosphorylation of MAPKs at 15 days may indicate a prominent protective role in the gills. The results show that sea bream and rock samphire can be used in brackish aquaponics systems with satisfactory growth performances, thus allowing for a range of commercial applications generating interest in their production.