In conclusion, the results of the current research indicated that ORP around 300–320 mV in fish tank had a negative influ-ence on the feed intake, feed conversion rate and growth rate.Meanwhile considering hematological parameters, it appears a simpossible for seabass to adapt to ORP of 300–320 mV. How everfish under 300–320 mV were less sensible to bacterial infection,which suggests that a slightly increased and well controlled ORPlevel (above 240–270 mV) has a positive effect. Consequently, wesuggest that ORP for seabass in RAS should be elevated but notexceeding 300 mV. A slight increase of the ORP level in RAS seems toimprove the water quality and the ability of the fish to react again stpathogenic bacteria. Moreover a strict control of the TRO level isstrongly suggested and further studies are necessary to identifyhow ORP alters the physiological fish parameters and microbe com-munity in both water and fish.