The Use of Kaolin as a Prophylactic Treatment to Prevent Columnaris Disease (Flavobacterium covae) in Commercial Baitfish and Sportfish Species

SIMPLE SUMMARY: The aquaculture industry suffers large financial losses every year to a bacterial disease known as columnaris. Columnaris can be treated with antibiotics in the feed, but this is expensive and can lead to antibiotic resistance. Alternative inert substances that are inexpensive and that would not lead to antibiotic resistance are needed. One such alternative is kaolin clay. This clay is added to the water and has been shown to bind to columnaris bacteria in laboratory studies. This study used kaolin clay on several species of game and sportfish stocked at commercial rates. When added to the water as a prophylactic treatment, the kaolin clay bound to columnaris. The kaolin clay did not damage the organs of the fish, nor did it cause mortalities. We have shown that kaolin clay is safe to use as a prophylactic treatment in several freshwater fish species raised in Arkansas, USA. ABSTRACT: 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 (AkuaPro(TM), 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.