World Aquaculture March 2019

WWW.WA S.ORG • WORLD AQUACULTURE • MARCH 2019 53 ( C O N T I N U E D O N P A G E 5 4 ) product is an equilibrium solution of these components that has long shelf stability. In addition, PAA breaks down quickly in the environment to water and acetic acid. It is a potent disinfectant and has replaced chlorine-based disinfectants or sanitizers in many industries. PAA has greater reactivity and lipid-penetrating properties than hydrogen peroxide alone and is not deactivated by catalase and peroxidase (naturally occurring on organismmembranes) like hydrogen peroxide. Thus, PAA eliminates unwanted organisms easier and faster. Most importantly, it is eco-friendly and does not leave dangerous residues, such as trihalomethanes and haloacetic acids when hypochlorite decomposes or reacts with naturally occurring organic matter. During a literature search, the earliest suggestion of using a PAA product as a disinfectant against fish pathogens was by the esteemed Wilhelm Schäperclaus (1991 translated from his 1986 German publication), who suggested a 1 percent solution of a commercially available 40 percent Wofasteril + 1 percent Graham’s salt as protection against corrosion. He stated that “the scope of disinfection includes fish parasites, bacteria, fungi, viruses, but not helminth eggs.” In the EU, PAA is approved for use in veterinary medicine and is one of the very few compounds approved for use in aquaculture as a disinfectant. PAA has been used in Denmark and Germany for some time to treat saprolegniasis and parasites such as Ichthyophthirius multifiliis (Ich). This approval is as a water disinfectant “for cleaning and disinfection of equipment and facilities in the presence, as well as in the absence, of aquaculture animals.” So, back to my quest in 2008. My first problemwas where to find a manufacturer of PAA in the U.S. There were only a few manufacturers: Enviro-Tech, FMC (now PeroxyChem), MinnTech and Solvay. I was familiar with FMC frommy toxicology days in grad school, so I contacted a chemist at the company to request a sample. I asked if they were interested in collaborating on aquaculture research but I was not sure if they were even familiar with aquaculture. Over the years I have built good relationships with the PeroxyChem people, who send us samples of PAA. I have been given credit for my “persistence.” Our initial studies were designed to study the toxicity of PAA to relevant aquaculture species and the effectiveness of PAA on aquatic pathogens at my research center in Stuttgart, Arkansas (SNARC). Thomas would investigate fungus and bacteria inhibition and experiment with parasites at his research center in Berlin, Germany (IGB). The addition of Dr. Lars-Fleming Pedersen to our collaboration in 2012 added expertise on PAA degradation, use in recirculating aquaculture systems (RAS) and stress and immune response, work undertaken at his research center in Hirtshals, Denmark (DTUAqua). We communicate by emails, video conferencing and occasional site visits. Accomplishments to Date As Thomas and I shared a research background working with Ich, we started there. Our first publication determined the acute toxicity of two products containing 4.5 percent and 40 percent PAA to Ich theronts, the free-swimming infective stage, from two geographically separate isolates (Straus and Meinelt 2007). We followed this up with another toxicity study on PAAwith Ich tomonts, the encysted reproductive stage, that was previously thought to be resistant to treatments (Meinelt et al. 2009). In 2009, I received a manuscript request from Lars-Fleming Pedersen, a Ph.D. student in Denmark, finishing his thesis on the fate of therapeutic treatments and their effects on biofilters in RAS (Pedersen 2009). He is now a Senior Researcher for DTUAqua in Hirtshals, Denmark. Several years later (~2012), I received a surprise phone call from Lars to discuss our individual research projects and to start collaboration efforts. Since Thomas was in closer proximity, he met with Lars and they have since shared research efforts on various national projects. Also in 2009, Thomas and his wife came for a working visit to my lab and to present our PAA research at the Aquaculture Drug Approval CoordinationWorkshop I was invited to organize in Little Rock, Arkansas. We continued our Ich publications with Dr. Eliška (nee Sudová) Zusková, one of Thomas’ collaborators from the Czech Republic to study the effectiveness of PAA on Ich-infested carp (Sudová et al. 2010). In 2011, I traveled to Thomas’ research center for a working visit to better understand his research approach and to present our PAA research at a conference held in Berlin, Germany. We then changed the focus of our research to using PAA to control fungus on catfish eggs (Straus et al. 2012a) and found that PAAwas 100 times more effective at controlling fungus than hydrogen peroxide. We followed that up with studies to determine the toxicity and histological effects of PAA on catfish fry (Straus et al. 2012b). Our next two publications came from one of Thomas’ Life-cycle of Ichthyophthirius multifiliis (Photo: Harry Dickerson). Catfish fingerlings covered with Ich (Photo: Cindy Ledbetter).