World Aquaculture March 2019

54 MARCH 2019 • WORLD AQUACULTURE • WWW.WA S.ORG students who carried out in vitro studies on Flavobacterium columnare and Saprolegnia parasitica to determine the effects of PAA on growth and determining the effect of water hardness on PAA toxicity to zebrafish embryos (Marchand et al. 2012, 2013). Lars’ research focused on verification of PAA concentrations under practical conditions of low dosage and the resultant PAA degradation. The difficulty in measuring PAA at low concentrations made it very challenging (Pedersen et al. 2013). We also had an opportunity to look at the effectiveness of PAA to treat a naturally occurring parasite outbreak in catfish (Farmer et al. 2013). In 2014, Dibo Liu, a student of Thomas, published some of his graduate research with investigations on the effects of salinity, dissolved organic carbon and water hardness on PAA degradation (Liu et al. 2014). Since then, he has been an extremely productive member of our collaboration. His research focus is on fish physiology, stress physiology, histopathology and biofilm degradation. Thomas came back to Arkansas in 2015 for a working visit to my lab and to present more of our collective PAA research at several meetings, culminating at Aquaculture America in NewOrleans. At the trade show, we were approached by AquaTactics Fish Health, as they were interested in gaining a label on a PAA product for the U.S. For the first time since starting this research, I saw a light at the end of the tunnel! Next, Dibo compared the toxicity of PAA products with different PAA:H 2 O 2 ratios to Daphnia to evaluate the effect of hydrogen peroxide on overall toxicity (Liu et al. 2015). To follow-up on Dibo’s research and continue with his in vitro studies, Thomas compared growth inhibition of bacteria exposed to six commercial PAA products (Meinelt et al. 2015). In 2015, Thomas, Dibo and I met for the International Conference on Diseases of Fish and Shellfish (EAFP) and introduced a new audience to our latest research, with three presentations about PAA, all of which were all very well- received. In early 2016, I talked with Dr. Chris Good at the Freshwater Institute in Shepherdstown, West Virginia, about incorporating PAA rather than hydrogen peroxide (we had indications it would work better) into his RAS research to reduce stress-derived fungus on fish. I also presented initial findings on our PAA toxicity studies at Aquaculture America 2016 and learned that people were using PAA to disinfect marine fish eggs (i.e., halibut, sablefish, baitfish). Learning this added more urgency to getting an EPA-approval for this disinfectant. Meanwhile, Dibo published the results of a study about using PAA products at concentrations (1 and 2 mg/L) that would not inhibit marine microalgae (Liu et al. 2016). The PAA researchers of our collaboration finally had a chance to meet at the 2016 International Conference on Recirculating Aquaculture in Roanoke, Virginia, where we gave several PAA presentations and got a chance to sit down and talk about future endeavors. Chris Good also presented his research using PAA to control post-vaccination saprolegniasis in Atlantic salmon in a RAS at several meetings (Good et al. 2016). At the end of the year, the folks at PeroxyChem informed me that they had submitted an aquaculture label request to EPA. More light!! In 2017, Dibo was awarded his Ph.D. with a dissertation on the Effect of Peracetic Acid at Low Concentrations on Fish Health and Water Quality (Liu 2016). He graduated summa cum laude and won the prestigious Federation of German Fisheries Administrators and Fisheries Scientists (VdFF) award in Germany for his innovative research. He has done several internships with Lars and is currently working as a post-doc in Thomas’ laboratory. Dibo continues to produce quality publications. Liu et al. (2017a) looked at two strategies for applying PAA and found that a single dose, two times per week, had advantages over continuous application. Liu et al. (2017b) applied PAA to a carp RAS every three or four days for five weeks and measured the stress response of the fish through plasma cortisol measurements once weekly. Results indicated that the fish adapted to the slight stress caused by PAA addition with no ill effects. Where We Are Now Two PAA products manufactured in the U.S. now have Environmental Protection Agency (EPA) registrations for use to sanitize harvesting equipment and disinfect culture facilities when fish are not present: PeroxyChem’s VigorOx ® SP-15 Antimicrobial Agent (EPA registration June 26, 2017) and AquaTactics Fish Health’s Aqua Des ™ (approved November 3, 2017). This would not have been possible without our international collaboration to bring attention to this compound. Our quest had been realized but our efforts are not done yet. Due to the very limited research on the safety of PAA to fish, Healthy catfish eggs (left) and eggs with fungus (right) (Photos: Cindy Ledbetter).