World Aquaculture Magazine - September 2021

WWW.WA S .ORG • WORLD AQUACULTURE • SEP TEMBER 2021 53 IncreasedAeration The adoption of intensive farming practices that increases aeration rate has resulted in a 68 percent increase in average paddlewheel aeration rate in the last decade. In addition to intensively aerated small ponds and split ponds, farmers have also increased aeration in traditional ponds. This was primarily due to the increased adoption of intensive systems and partly due to the availability of excess available aerators due to the reduction of the total number of ponds in the industry. AutomatedOxygenMonitoring Systems The increased adoption of intensive systems and increased aeration rates in the industry also resulted in greater adoption of automatic oxygen monitoring systems. A recent survey revealed that 96 percent of the surveyed catfish farms had adopted automated oxygen monitoring systems as a complementary technology to manage pond dissolved oxygen levels. Vaccines In 2008, Dr. David Wise at the Mississippi State University – Thad Cochran National Warmwater Aquaculture Center, began work developing an oral vaccination platform to immunize fish against enteric septicemia of catfish (ESC), a bacterial disease causing significant economic losses in the US catfish industry. There is also evidence that the ESC vaccine cross-protects against E. piscicida , an emerging pathogen in larger hybrid catfish (Griffin et al. 2020). A crucial step in this process was the development of a mechanized system for preparing the vaccine-feed mixture at the point of delivery. Large-scale commercial trials began in 2016 and the vaccine became commercially available in 2018. The patented vaccine and vaccine delivery system (Wise et al. 2015) are currently being used to vaccinate channel and hybrid catfish resulting in increased yield and economic returns in fingerling and foodfish production. Improvements in survival, feed consumption and feed conversion resulting from vaccination are producing additional economic benefits as a result of diffusion of benefits from the fingerling production phase to the stocker ( C O N T I N U E D O N P A G E 5 4 ) ponds (3-6 ha) used in catfish farming. Smaller ponds are easier to completely mix with aerator currents. Currents produced by paddlewheel aerators tend to dissipate in larger ponds beyond a particular zone of influence by aerators, leaving large areas of the pond non-aerated. Also, it is possible to produce 10-20 t of catfish/ha per year (Kumar and Engle 2017a,b) under commercial conditions in intensively aerated small ponds. This level of production in large ponds would increase risk and make it difficult to coordinate harvest with processing plants. Complementary Technologies The advent of these intensive production systems has led to increased adoption of complementary technologies such as hybrid catfish fingerlings, increased aeration rates, automated oxygen monitoring systems and vaccines. These complementary technologies are essential productivity increasing inputs in intensively aerated ponds and split-pond systems. Hybrids Hybrid catfish are considered as a complementary technology in intensive catfish production systems. Hybrid catfish have the advantage of increased resistance to disease and parasites, better tolerance of crowded systems and more aggressive feeding behavior resulting in faster growth. Research and outreach efforts by the USDA-ARS Warmwater Aquaculture Research Unit and Auburn University helped commercial producers increase production of hybrid catfish from an estimated 5 million hybrid fingerlings in 2005 to 315 million in 2019. The recent industry survey (Hedge et al. 2021) found that 53 percent of the US catfish production area was in hybrid catfish production. The survey of fingerling producers found that about 60 percent of the catfish fingerlings produced in the industry were hybrid catfish. An alternative metric of adoption of hybrid catfish obtained from catfish processing plants suggested that 58 percent of the round weight processed were hybrid catfish. All three measurements found increased adoption of hybrid catfish in the catfish industry with adoption ranging from 53-60 percent depending on the metric considered. FIGURE 4. Percentage of catfish production area under various production technologies. FIGURE 3. Gross yield (kg/ha) for traditional ponds (n=218), intensively aerated ponds (n=54) and split ponds (n=102).