Recirculating Aquaculture Systems (RAS) present an innovative, clean and practical way of producing fish intensively. Stress caused by high concentrations of chemical species such as nitrite and un-ionized ammonia, affects fish health and growth and therefore the sustainability of RAS would require an online monitoring for those chemical stressors. This work reveals a study on the suitability of Aliivibrio fischeri as a toxicity sensor for un-ionized ammonia and nitrite. Temperature variation effects were also considered. An EC50 of 0.17 mg/L was found for nitrite and 0.57 mg/L for un-ionized ammonia. It was concluded that Allivibrio fischeri is suitable as an indicator for nitrite in aquaculture at optimal salinity and temperature conditions.