62 DECEMBER 2012 • WORLD AQUACULTURE • WWW.WAS.ORG This discussion about personal experiences related to progress in water quality management in pond culture of sportfish, channel catfish, and marine shrimp since the early 1960s is based on a presentation made in the Aquaculture Pioneers session of Aquaculture America 2012. Production levels in ponds were rather low 50 years ago; impaired water quality occurred infrequently and was not considered a major limitation. The emphasis was on finding and domesticating new aquaculture species, designing culture methods, developing feeds, and seeking ways to minimize losses to diseases and parasites. Improvements in these areas, however, allowed farmers to increase production intensity up to limits imposed by water quality — usually inadequate natural productivity in sportfish ponds and low dissolved oxygen (DO) concentration in commercial aquaculture ponds (Boyd and Tucker 1998). Sportfish Culture Ponds are common features of the landscape in the United States. Examination of satellite images revealed 8 to 9 million small water bodies in the United States (Renwick et al. 2005), and over 2 million of these entities are manmade ponds large enough for fish propagation (USDA-SCS 1982). These ponds were built mainly for farm water supply and conservation purposes, but investigations of sportfish culture in farm ponds by Homer S. Swingle and his associates that began in the 1930s at Auburn University popularized ponds for recreational fish culture — mainly a combination of sunfish Lepomis spp. and largemouth black bass Micropterus salmoides. A substantial but unknown proportion of ponds are managed to various degrees for this purpose. Research on fertilization, liming, and other sportfish pond water quality issues was recently reviewed (Boyd, in press) and the discussion here will be limited to comparing water quality management of sportfish ponds between the 1960s and today. The principles of liming were poorly understood in the 1960s. Procedures were not available for deciding whether or not a pond should be limed and for determining how much liming material to apply. Broadcast applications of granular fertilizers were used exclusively to promote phytoplankton blooms. Today, a bottom soil sample from a pond may be sent to a soil testing laboratory where a procedure developed specifically for pond bottom soils (Boyd 1974, Pillai and Boyd 1985) can be used to provide a liming recommendation. Liquid fertilizers were demonstrated to be more effective and easier to apply than granular fertilizers (Metzger and Boyd 1980, Boyd 1984); they have largely replaced granular fertilizers for use in sportfish ponds. Some pond owners also may apply feed to increase production beyond that possible in traditional, fertilized ponds (Halley et al. 2012). Aquatic macrophyte control in ponds was often by herbicide treatment when it could not be achieved through use of fertilizers to produce turbidity and shade underwater plants (Davison et al. 1962). The use of grass carp Ctenopharyngodon idella is now a common means of aquatic macrophyte control (Masser 2002). Removal of turbidity caused by suspended soil particles formerly was achieved by organic matter applications. Today, erosion control on watersheds and pond embankments and edges is promoted, and if turbidity still persists following application of these practices, it can be removed with coagulants such as aluminum sulfate or calcium sulfate (Boyd and Tucker 1998). Pond waters often stratify thermally and sudden destratification may follow heavy rain and strong wind associated with weather fronts in summer, leading to DO depletion and fish kills. Destratification devices — such as a grid of air diffusers placed on the pond bottom — may be used to prevent stratification (Boyd and Tucker 1998). Pond owners originally relied almost entirely on information from universities or state game and fish agencies as guidelines for pond management. Today, many pond owners contract with commercial pond management services to manage their ponds. Channel Catfish Culture Channel catfish Ictalurus punctatus culture apparently was first conducted in Kansas in the 1940s, but the present-day commercial industry began in the 1960s in Alabama and soon spread to other southern states — especially Mississippi and Arkansas. Production was initially less than 2000 kg/ha, but with development of better feeds, production could exceed the capacity of pond ecosystems to oxidize the resulting organic and nitrogenous wastes and maintain acceptable DO concentration for fish (Boyd and Tucker 1998). In the early days of catfish farming, the occurrence of low DO concentration usually was known only when fish were seen gasping at the surface. There were no DO meters and the Winkler method Personal Experiences in Pond Water Quality Management Claude E. Boyd1
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