2.1. Recirculating aquaculture systems and ORP control
Two RASs, each consisting of three tanks, were located at Ifremer
(Palavas les Flots Station, Montpellier, France). The experimental
system, in which ORP was elevated by ozone injection into a skim-
mer, was called RAS-O3. The control system was referred to as
RAS-C. Details of the construction of the systems and of the ORP
controllers were reported in Li et al. (2014).
During the whole experimental period of 90 days, the ORP
level of the fish tanks in RAS-O3 was maintained between 300 and
320 mV. The ORP level of RAS-C was kept in the range 240–270 mV.
Four ODEON devices (Ponsel, France) were used to monitor the ORP
levels and other water quality parameters, including pH, oxygen
concentration, and temperature in the fish tanks of both RAS-C and
RAS-O3.
In both systems, the oxygen concentration was adjusted daily to
around 110% saturation at the outlets of the fish tanks, temperature
was maintained at 21 ◦C, and pH was maintained at about 7.8 at the
outlets by injecting sodium hydroxide into the pump tank.