The effects of ozonation on select waterborne steroid hormones in recirculation aquaculture systems containing sexually mature Atlantic salmon Salmo salar

Authors: GOOD, CHRISTOPHER - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute; EARLEY, RYAN - University Of Alabama; STYGA, JOSEPH - University Of Alabama; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2017
Publication Date: 12/1/2017
Citation: Good, C., Davidson, J., Earley, R.L., Styga, J., Summerfelt, S.T. 2017. The effects of ozonation on select waterborne steroid hormones in recirculation aquaculture systems containing sexually mature Atlantic salmon Salmo salar. Aquacultural Engineering. 79:9-16. https://doi.org/10.1016/j.aquaeng.2017.08.004.
DOI: https://doi.org/10.1016/j.aquaeng.2017.08.004

Interpretive Summary: Steroid hormones have been shown to accumulate in recirculation aquaculture system (RAS) water over time; however, their influence on the reproductive physiology of fish within RAS remains unknown. Whether ozonation impacts waterborne hormone levels in RAS has likewise not been fully evaluated. To this end, a controlled 3-month study was conducted in 6 replicated RAS containing a mixture of sexually mature and immature Atlantic salmon Salmo salar to determine whether ozone, as typically applied in RAS to improve water quality, is associated with a reduction in waterborne hormones. We determined that estradiol was significantly reduced by ozonation, and that testosterone and 11-ketotestosterone (11-KT) were also reduced by ozonation although not observed in all instances. Biofiltration, regardless of water ozonation, significantly reduced both testosterone and 11-KT concentrations following water passage through the RAS fluidized sand biofilters. The results of this study demonstrate the potential for ozone to be used in RAS as a means of preventing the accumulation of steroid hormones. Further research is required to assess whether reducing hormones in this manner impacts precocious sexual maturation in RAS-produced Atlantic salmon.

Technical Abstract: A controlled 3-month study was conducted in 6 replicated water recirculation aquaculture systems (RAS) containing a mixture of sexually mature and immature Atlantic salmon Salmo salar to determine whether water ozonation is associated with a reduction in waterborne hormones. Post-smolt Atlantic salmon (1,253 plus or minus 15 g) were stocked into each RAS; 109 of 264 fish placed in each system were sexually mature males, and 5 were mature females. Water ozonation, controlled using an oxidation-reduction (ORP) set-point of 290-300 mV, was applied with the pure oxygen feed gas within the low-head oxygenators of 3 randomly selected RAS, while the remaining 3 RAS did not receive ozone. The RAS hydraulic retention time was 6.9 plus or minus 0.3 days. Study fish were raised under these conditions for 12 weeks; during weeks 10 and 12, triplicate water samples were collected from the following locations in each RAS: i) culture tank, ii) makeup water, iii) pre-biofilter, iv) post-biofilter, and v) post-gas conditioning. Concentrations of 3 waterborne hormones - testosterone, 11-ketotestosterone (11-KT), and estradiol (17ß-estradiol) - were quantified using enzyme immunoassays (EIA). Estradiol was significantly reduced by ozonation; testosterone and 11-KT were also reduced by ozonation, although these reductions were not observed across all sampling locations and events. Testosterone and 11-KT concentrations, however, were significantly reduced following water passage through the biofilters of both ozonated and non-ozonated RAS. The results of this study demonstrate the potential for ozone to be used in RAS as a means of preventing the accumulation of steroid hormones.