Effects of ozone on post-smolt Atlantic salmon (Salmo salar) performance, health, and maturation in freshwater recirculation aquaculture systems

Authors: DAVIDSON, JOHN - Freshwater Institute; SUMMERFELT, STEVEN - Superior Fresh; MOTA, VASCO - Nofima; ESPMARK, ASA MARIA - Nofima; MARANCIK, DAVID - St George'S University; EARLEY, RYAN - University Of Alabama; SNEAD, ANTHONY - University Of Alabama; GOOD, CHRISTOPHER - Freshwater Institute

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2020
Publication Date: 12/2/2020
Citation: Davidson, J., Summerfelt, S., Espmark, A.O., Mota, V., Marancik, D., Earley, R., Snead, A., Good, C. 2020. Effects of ozone on post-smolt Atlantic salmon (Salmo salar) performance, health, and maturation in freshwater recirculation aquaculture systems. Aquaculture. 533, 736208. https://doi.org/10.1016/j.aquaculture.2020.736208.
DOI: https://doi.org/10.1016/j.aquaculture.2020.736208

Interpretive Summary: Precocious maturation is a consistent problem for the production of market-size Atlantic salmon in recirculation aquaculture systems (RAS), because it results in reduced fillet quality, slow growth, poor feed conversion, and decreased revenue for farmers. Reproductive maturity is triggered by a range of environmental and biological cues, and the exact reason(s) for increased salmon maturation in RAS are therefore unknown. As such, a study was carried out to investigate the potential for ozone (a water treatment technology) to oxidize and reduce waterborne hormone concentrations and their effect on salmon maturation. Replicate RAS were operated with and without ozone addition while rearing immature, mixed-sex Atlantic salmon. Certain dissolved hormone concentrations were reduced by ozone; however, salmon maturation was not inhibited. Nevertheless, the use of ozone resulted in significant water quality improvements and faster Atlantic salmon growth, which could reduce the fish production duration and result in diminished production costs. Additional research is still required to define the environmental and biological variables that limit early Atlantic salmon maturation in RAS.

Technical Abstract: Steroid hormones accumulate in recirculation aquaculture systems (RAS) and may influence the reproductive physiology of fish. Ozone reduces waterborne hormones in freshwater RAS used to rear maturing Atlantic salmon, but its effect on reproductive onset is unknown. Accordingly, a study was carried out to evaluate the growth, health, and reproductive physiology of post-smolt Atlantic salmon (296 ± 4 g initial weight) in replicated freshwater RAS operated with or without ozone (N = 3). Residual ozone levels were maintained via oxidation reduction potential at a setpoint of 300-320 mV. Atlantic salmon growth was faster in ozonated RAS throughout the experiment. Salmon from RAS with and without ozone weighed 2,156 ± 101 and 1,810 ± 15 g, respectively by the end of the 8-month trial. Caudal, anal, and pelvic fin damage was greater for salmon reared in ozonated RAS early in the study but improved thereafter. Waterborne estradiol was lower in ozonated RAS at each sampling point, and testosterone and 11-ketotestosterone were generally lower, albeit not significantly. Nevertheless, maturation onset occurred sooner and was more prevalent for salmon reared in ozonated RAS. By study’s end, percent maturation for salmon reared in RAS with and without ozone was 63 ± 7 and 48 ± 1 % of the population, respectively. Under conditions of this study, ozone did not inhibit the onset or prevalence of Atlantic salmon maturation, but significant improvements in water quality and salmon growth performance resulted from its use.