Aquaculture farms in Arkansas, USA routinely battle columnaris disease caused by Flavobacterium covae. Columnaris is prevalent during stressful events such as feed training and when fish are stocked at high densities in holding vats before sale. Kaolin clay was effective in laboratory trials as a treatment for columnaris in catfish. As a result, fish farmers are interested in applying kaolin products but were hesitant as they feared that the high doses of kaolin clay in vats might negatively affect the gills and overall health of fish. Therefore, we evaluated potential clay concentrations that might be used to prophylactically treat fish in vats. The effects of low to excessively high doses (0, 1, 2, 4, or 8 g/L) of kaolin clay (AkuaProTM, Imerys, GA, USA) were evaluated using a 72 h bioassay conducted in static tanks using Micropterus salmoides, Pomoxis nigromaculatus, Lepomis macrochirus, Ictalurus punctatus, Notemigonus crysoleucas, and Pimephales promelas. Results of these trials revealed a 100% survival rate across all six fish species exposed to kaolin clay at concentrations of up to 8 g/L for 48 h (followed by a 24 h recovery period in clean water) with no adverse effects to eyes, skin, gastrointestinal tract, or liver histology noted at any treatment. In addition, Micropterus salmoides analyzed for heavy metals due to exposure to the clay indicated that concentrations did not differ from control fish.
Keywords: Flavobacterium covae; columnaris; kaolin clay.