Aquaculture CRSP 21st Annual Technical Report
Workshops on Using Principles of Pond Dynamics to Optimize Fertilization Efficiency
Tenth Work Plan, Pond Dynamics Research 2 (10PDR2)
Ted R. Batterson, Christopher F. Knud-Hansen, and Donald Garling
Department of Fisheries and Wildlife
Michigan State University
East Lansing, Michigan, USA
School of Environmental Research and Development
Asian Institute of Technology
Eight, three-day workshops were given in Bangladesh, Cambodia, Laos, Nepal, Thailand, and Vietnam during June to July 2002. These workshops focused on practical aspects of how to use principles of pond dynamics to improve pond management and optimize fertilization efficiencies for natural food production in semi-intensive aquaculture systems. The centerpiece of the workshops was learning how to apply the algal bioassay fertilization strategy (ABFS) using the simple algal bioassay test kit developed by Michigan State University (MSU) through the Aquaculture Collaborative Research Support Program (CRSP). Fifteen test kits were left at each workshop site. Nearly 150 total participants representing universities, government fisheries offices, non-profit organizations, and community farming groups participated in the workshops. Responses to the workshops have been very positive. Reports from several countries indicate that researchers and farmers alike are adopting the ABFS because it is practical and promotes economically-efficient natural food production by using a simple ecological approach to identify pond-specific fertilization requirements.
Pond fertilization in aquaculture is intended to stimulate phytoplankton productivity in order to provide natural foods for culture organisms (Colman and Edwards, 1987; Schroeder et al., 1990). Research on pond fertilization to increase yields of planktivorous fish, particularly Nile tilapia (Oreochromis niloticus), has received considerable attention at Aquaculture CRSP research sites located in Southeast Asia, Latin America, and Africa (Egna, 1997). The scientific foundation for this research is the well-established, empirical positive relationship between algal productivity and the net fish yield (NFY) of planktivorous and detritus-feeding fish (e.g., McConnell et al., 1977; Almazan and Boyd, 1978; Oláh et al., 1986; Knud-Hansen et al., 1993). This relationship is quite logical because algal productivity is the energetic foundation for secondary production and detritus formation, and all three are basic and valuable food sources for omnivorous and detritivorous fish (Schroeder et al., 1990).
The five principle factors that regulate algal productivity in ponds are the availabilities of soluble inorganic nitrogen (N), phosphorus (P), carbon (C), light, and suitable water temperatures (Fogg, 1975). Pond fertilization supplies
soluble N, P, and C for algal uptake and growth, while the availabilities of sufficient solar radiation and appropriate temperatures are functions of weather, pond location, and pond turbidity. Relative deficiencies in any one or more of these requirements will depress and possibly cease phytoplankton productivity until that requirement is satisfied. When such a requirement has become a limiting factor, phytoplankton growth will be controlled by the availability of that factor regardless of the concentrations of non-limiting nutrients (O'Brien, 1974). For example, N fertilization of a pond in which P availability limits algal growth will have little or no effect on algal productivity in that pond (e.g., Boyd and Sowles, 1978). To maximize fertilization efficiency, inputs of N, P, and C must neither limit phytoplankton growth nor exceed phytoplankton demands. When all algal nutrient requirements are met, algal productivity may be limited by physical factors such as unfavorable water temperatures or insufficient light availability due to algal self-shading and/or inorganic turbidity.
Since the mid-1980s, research conducted by MSU through the Aquaculture CRSP has focused on incorporating ecological principles of pond dynamics (e.g., N and P cycling, dissolved oxygen dynamics, thermal stratification, primary