64 DECEMBER 2012 • WORLD AQUACULTURE • WWW.WAS.ORG The paddlewheel design was presented at a scientific meeting in Las Vegas, Nevada in 1988. The next week, I looked out the window of my office and saw a truck entering the parking lot, carrying an aerator with a paddlewheel that conformed to the design presented at the meeting (Fig. 2). A machine shop owner who sold equipment to catfish farmers had heard the presentation, made an aerator following our recommendations, and offered it for testing. The device performed quite well, and soon several machine shops were fabricating aerators according to the improved design — of course, each fabricator added his own touch. The success of the aerator design brought me a lot of grief. The owner of a company that manufactured another type of aerator for catfish ponds began complaining about losses of sales and even threatened legal actions against the university. Eventually I was asked to stop research on aerators. Nevertheless, the project had been successful, and aeration allowed an increase in catfish production. The research on aerators had been partially funded by a grant from the USDA-BARD program. In 1998, an economic consultant was employed by BARD to assess the monetary benefits attributable to some of their grants. According to the consultant’s assessment, the paddlewheel design lead to a 20 percent increase in catfish yield at a production cost increase of 11 percent. The adoption rate by the industry was estimated at 80 percent and benefits in 1998 alone were placed at US$87 million with projected cumulative benefits of US$1.5 billion by 2010. Obviously I should have patented the design! Automation of aeration by using sensors that turn aerators on and off in response to DO concentration can save energy (Hoagland et al. 2001) and is becoming quite common. The first attempt to commercialize aerator controllers for catfish farming was by a retired electrician. The prototypes were installed in ponds at Auburn University and they functioned quite well for short periods. However, DO sensor probes malfunctioned often because of biofouling, and circuitry controlling the aerators was sensitive to lightning strikes in the vicinity. This unfortunate fellow went broke for trying, but others took up his idea and made fairly reliable automation systems that have received a modest degree of adoption by catfish farmers. Other important advances in water quality management for catfish ponds were the use of sodium chloride to counteract nitrite toxicity, copper sulfate to control phytoplankton responsible for off-flavor, more precise information on the effects of low DO concentration, and a better understanding of nitrogen dynamics in ponds. Most of this research was conducted at the Mississippi State University Delta Research and Extension Center, and the findings have been summarized (Tucker and Hargreaves 2004, 2011). Marine Shrimp In 1985, Auburn University had USAID-funded aquaculture projects in Panama and Ecuador. During visits there, project leaders arranged for me to give workshops on water quality management at which several shrimp farmers were among the attendees. There had been little research on water quality in shrimp ponds up to that time but there were many real and perceived water quality issues. As a result of these workshops, I was suddenly in demand as an advisor to shrimp farms, international development agencies, shrimp farm suppliers in Central and South America, and later in Asian countries and Madagascar. For several years, I relied on modifying water quality findings from sportfish and channel catfish pond aquaculture for use in shrimp aquaculture. I presented many workshops to shrimp farmers and my water quality book, originally published in 1979 and later revised in 1990, became popular. Around 17,000 copies of the English version have been sold and it has been translated to Thai, Spanish, Indonesian, and Chinese. Some large farms sponsored several of my Ph.D. students to conduct on-site research on shrimp pond water quality. Moreover, several universities and research organizations began to conduct research on water quality in shrimp ponds. Today, there is a large body of research findings to support water quality management in shrimp ponds. Shrimp farmers originally applied high rates of water exchange for improving water quality. After the onset of devastating viral diseases in the 1990s, farmers came to understand that water exchange could spread shrimp diseases. Today, many shrimp producers disinfect water in ponds before stocking shrimp, exchange no water during the grow-out period, and disinfect “make-up” water for replacing evaporation and seepage losses. In Asia, shrimp farmers apply many amendments to ponds in hopes of improving water quality (Gräslund et al. 2003). The most commonly-used products are mineral mixtures, zeolite, living bacterial cultures, and enzyme preparations. Research findings or logic do not support use of these products (Boyd and Tucker TOP TO BOTTOM: Early catfish pond aerator. Impressive but inefficient aerator. Basin for testing aerators at Auburn University.
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