Post by Brad Richardson.—In July of 2015, I began my first summer of work on my doctoral research. My research is focused on a bacterial disease having a huge detrimental impact on the catfish aquaculture industry that is so prevalent in the southeastern United States. The disease had been around for approximately 6 years and showed no signs of slowing down, costing the catfish industry tens of millions of dollars in lost revenue each year. At that time, channel catfish (Ictalurus punctatus) was the primary species being cultured in the ponds of Alabama, Mississippi, and Arkansas. However, a new group of fish was also on the rise – hybrids. Hybrid catfish are the product of fertilizing the eggs of a female channel catfish with sperm from male blue catfish (Ictalurus furcatus). Hybrid species often express a phenomenon called "hybrid vigor" which can manifest in a variety of ways including increased growth and disease resistance. The hybrid catfish were no different! The fish showed significant increases in growth rates, feed conversion (e.g. amount of feed needed to produce 1 lb. of fish), and disease resistance.

This new stock of fish was praised by the farmers, and as their popularity grew so did the number of farmers stocking them. This left my research in vulnerable position; our primary goal was to help the catfish industry…but we still needed disease outbreaks. As you can imagine, that's not easy to tell a farmer that is trying to make a living. Over the last 4 years, the proportion of Mississippi farms using hybrid catfish has increased from approximately 15% to nearly 50%. Unfortunately, many of these farms are discovering that the hybrid vigor that lead to the increased resistance to channel catfish diseases had little/no effect on other diseases. Problems, new and old, have continued to plague the hybrid catfish including Edwardsiella piscicida (bacterial disease), Columnaris (bacterial disease), and Proliferative Gill Disease (parasite disease). So, the hybrid expansion has begun to slow as farmers are starting to stock both species of catfish on their farms.

Changing fish stocks is the not the only industry shift we have experienced in the last 4 years, changing feed compositions, feeding rates, stocking rates, pond management, disease monitoring, and water quality management have all seen some degree of change. These changes each provide their own set of challenges when conducting fish disease research. And you have to find a way to maintain some type of continuity in the face of the constantly changing industry.