EFFECTS OF SEMI-CONTINUOUS PERACETIC ACID DOSING ON RAINBOW TROUT Oncorhynchus mykiss PERFORMANCE, WATER QUALITY, AND OFF-FLAVOR COMPOUNDS IN RECIRCULATION AQUACULTURE SYSTEMS
Water clarifying and disinfection techniques such as ozonation and ultraviolet irradiation are commonly used in recirculation aquaculture systems (RAS); however, the capital and operating costs of these technologies are expensive. Cost-effective treatment options that maintain fish health and simultaneously improve water quality without impacting nitrification are still required. Peracetic acid (PAA) has shown potential as an effective aquaculture chemotherapeutant that, at certain doses, is compatible with biofiltration and may provide water quality advantages. The comprehensive effect of regular PAA dosing on RAS water quality, fish health and performance, and off-flavor compounds requires further study.
A trial was conducted using six replicated 9.5 m3 RAS; three operated with semi-continuous PAA dosing and three without PAA addition, while culturing rainbow trout (Oncorhynchus mykiss). Target PAA doses ranging from 0.05-0.30 mg/L were evaluated at 1-2-month intervals. Concentrated peracetic acid must be handled with caution, and as such, a safe and effective method for handling, storage, and dosing was developed. VigorOx®-SP15 (Peroxychem) was used as the PAA source and was dosed via peristaltic pumps to the inlet headspace of low head oxygenators (LHOs) of respective RAS. A water recycle rate >99% was maintained, and system hydraulic retention time averaged 2.7 days.
Rainbow trout growth performance was not affected by semi-continuous PAA addition at any of the doses evaluated. Preliminary analyses indicate that oxidative reduction potential (ORP) and true color were affected at certain PAA doses. ORP was generally greater in RAS where PAA was added and true color was slightly lower. Nitrification was not negatively impacted. In addition, concentrations of the off-flavor compounds geosmin and 2-methylisoborneol in water, biofilm, and trout fillets were not affected by PAA at the tested doses.
Overall, peracetic acid dosing within the selected concentration range was compatible with rainbow trout production and RAS operation. However, PAA dosing did not create dramatic improvements in true color and did not improve total suspended solids, biochemical oxygen demand, dissolved metals, or ultraviolet transmittance levels, as has been reported in previous experiments when applying a relatively low, non-disinfecting ozone dose. The effect of PAA on ORP is an important finding and indicates potential for continuously monitored ORP to be integrated as an on/off control for PAA dosing in RAS.