World Aquaculture Magazine -December 2021

WWW.WA S .ORG • WORLD AQUACULTURE • DECEMBER 2021 41 Nuño et al. 2019, 2018, Wiyoto et al. 2016). The regular use of Eh in relation to pH and EC to predict plant health and the development of pests or pathogens in soil systems has become more standardized in recent years (Bousset et al. 2019, Cottes et al. 2020, Husson 2012, 2013, Husson et al. 2018a, 2018b). Similarly, pH and EC are widely used to manage aquatic animal health, although Eh is a less informative metric in comparison to DO (Boyd 2016). Nonetheless, the impact of Eh on organisms at a cellular level is similar in eukaryotes and prokaryotes (Santos et al. 2018). When challenged, biological processes counterbalance oxidative stress (severe shift in local Eh) via the production of antioxidants (e.g., superoxide dismutases, catalases, glutathione peroxidases, and glutathione reductases) (Go and Jones 2017, Million and Raoult 2018, Sánchez-Nuño et al. 2019). Biological systems that fail to reestablish redox balance after a stress event suffer from long-term effects such as decreased growth rate, reproductive inhibition and chronic inflammation (Franco and Vargas 2018, Kohen and Nyska 2002, Li et al. 2015, Pradedova et al. 2017, Wang et al. 2018). The further homeostasis is perturbed —whether reduced or oxidized — the more difficult the rebound, leading to increased susceptibility to injury, predation and disease (Million and Raoult 2018, Sánchez-Nuño et al. 2019, Khattak 2020). Extreme shifts in pH on a cellular level can disrupt proton membrane transport resulting in decreased growth rates, weakened defensive mechanisms and cellular inactivation (Aoi and Marunaka 2014). Indirect effects such as changes in mineral mobility may result in disparate nutrient bioavailability or, at a lower pH, may Introduction Aquaponics is a rap- idly growing industry at the crossroads between two of the fastest-growing agricultural sectors — aquaculture and hydropon- ics — uniquely oriented as an ecologically sustainable and water-efficient food production system. Man- agement of aquaculture wastes and water for opera- tion of hydroponic systems creates unique challenges inasmuch as the reuse of nutrients in an integrated system limits the avail- able intervention for health management. Extensive research in agronomy and aquaculture have established the biological significance of parameters such as the redox potential (Eh), H (aq) + con- centration (pH), and electric conductivity (EC) to monitor the health of aquaculture and hydroponic systems. Howev- er, the interplay between Eh, pH and EC in relation to disease and pest management is underex- plored despite extensive research on the individual significance of these factors. Here we examine how knowledge of Eh, pH and EC can serve as key metrics of fish and plant health when considering the interrelationships among these factors. Physicochemical parameters are regularly measured as proxies for water quality metrics in the aquaculture industry (Boyd and Tucker 2015). These relationships rely on an underlying causality between the measured parameter and essential biological functions within the cultured organisms and environmental microorganisms. What is currently lacking in the literature is a contextualization of the interplay between common physicochemical parameters within target organism productivity and health in aquaponics systems. Interpreting physicochemical parameters has direct implications for farmers, as these parameters have been directly associated with disease and pest susceptibility in plants and animals (Li et al. 2015, Robinson et al. 2015, Sánchez- Improving Fish and Plant Health through Manipulation of Eh, pH and EC Interplay in Aquaponic Systems George J. Pate, Victor Lobanov and Alyssa Joyce Plant nutrient availability and toxicity in soils with respect to Eh and pH, and how they may dictate the occurrence of pests and diseases in plants. ( C O N T I N U E D O N P A G E 4 2 ) Extensive research in agronomy and aquaculture have established the biological significance of parameters such as the redox potential (Eh), H(aq)+ concentration (pH), and electric conductivity (EC) to monitor the health of aquaculture and hydroponic systems. However, the interplay between Eh, pH and EC in relation to disease and pest management is underexplored despite extensive research on the individual significance of these factors.