production and decomposition, and the role of inorganic turbidity) into pond fertilization recommendations for semi-intensive aquaculture. Pond management decisions on where to place the ponds, types of source water, pond depth and surface area, and managing pond sediments are all affected by pond dynamic considerations. In particular, understanding pond ecology promotes knowledgeable choices of appropriate fertilizers to both optimize fertilization efficiency and minimize unwanted environmental impacts (Shevgoor et al., 1994; Knud-Hansen, 1998).
In addition to studying pond dynamics, MSU also developed the ABFS to determine pond fertilization requirements on a pond- and time-specific basis (Knud-Hansen, 1998; Knud-Hansen et al., in press). The algal bioassay is a simple, ecologically-responsive test where pond or lake water subsamples are fertilized (spiked) with algal nutrients (e.g., N, P, and C) individually and in combination. Fertilizing with the primary limiting nutrient(s) will cause algae to grow. A secondary limiting nutrient is one that becomes limiting once the primary limiting nutrient is supplied. For example, algae in pond water with no soluble N and little soluble P will grow with N added, but not with additional P. N is the primary limiting nutrient. With N added, however, the available P is soon depleted and algal growth stops. When N and P are added together, however, algal growth is much greater than with the addition of N alone. P is the secondary limiting nutrient and must be added with N to get the pond green. The ABFS also identifies co-limitation (e.g., when N and P are both primarily limiting and the addition of either N or P alone does not stimulate algal growth), and light limitation (e.g., due to high algal biomass and/or inorganic turbidity causing insufficient light availability for the algae to utilize the added nutrients). Recommended fertilization is at a full rate for primary limiting nutrient(s), half rate for secondarily limiting nutrient(s), and no fertilization if the nutrient is not limiting at all.
The ABFS has been tested under controlled and field conditions, and it has proven superior in terms of nutrient fertilization efficiencies and farm economics to standard fertilization recipes and fertilization requirements determined by computer modeling (Knud-Hansen et al., in press). Variabilities between ponds (and within the same pond over time) limit the utility of fixed-input fertilization recipes, and explain why ponds fertilized identically will give an unpredictable range of fish yields. Although both computer models and the ABFS are ecologically based, the time, costs, and level of expertise required to use computer models makes farmer adoption impractical. The benefits of the ABFS are both economical and environmental. Fertilization requirements are fine-tuned on a pond-by-pond basis, so algal productivity is maximized with the minimal amounts of nutrients added. Fish yields are more consistent and predictable,
and there is minimal excess accumulation of N and P in the pond water, so environmental effects upon discharge are reduced. Furthermore, the ABFS eliminates the risk of ammonia toxicity because over-fertilization with N is impossible. In 2002, MSU developed a portable algal bioassay kit (described below) that requires no water chemistry, electricity, computers, or even literacy to use.
The activity described by this final report consisted of making about 130 algal bioassay test kits and giving three-day workshops at different institutions in South and Southeast Asia where the Aquaculture CRSP or the Asian Institute of Technology (AIT) aquaculture program or both have established formal connections. The primary objective of the workshops was to transfer existing scientific knowledge, generated through the Aquaculture CRSP, on how to improve the predictability of pond management and productivity through a practical understanding of pond dynamics.
Methods and Materials
Workshop Locations and Dates:
The three-day workshops were given by Knud-Hansen at the following dates and locations where the Aquaculture CRSP or the AIT aquaculture program or both have established formal connections. AIT served as the "home base" between workshops at other sites:
31 MayÐ3 June 2002 Aquaculture and Aquatic Resources Management (AARM), AIT, Pathumthani, Thailand
5Ð7 June 2002 Udornthani College of Agriculture and Technology (UCAT), Udornthani, Thailand
10Ð12 June 2002 Regional Development Coordination for Livestock and Fisheries (RDC), Savannakhet, Laos
17Ð19 June 2002 Faculty of Fisheries, University of Agriculture and Forestry (UAF), Ho Chi Minh City, Vietnam
20Ð22 June 2002 School of Agriculture Prek Leap (SAPL), Phnom Penh, Cambodia
27Ð29 June 2002 Research Institute for Aquaculture (RIA-1), Bac Ninh, Vietnam
3Ð5 July 2002 Fisheries and Aquaculture Department, Institute of Agriculture and Animal Science (IAAS), Tribhuvan University, Rampur Campus, Chitwan, Nepal
9Ð11 July 2002 Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh
Workshop Topics:
The workshop objectives were to teach principles of pond ecology which have a direct relationship towards efficient pond management through demonstrations, presentations,