Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment
Evaluation of Inorganic Nitrogen and Phosphorus Fertilization Techniques for Carp Ponds
David A. Culver, Lisa Babcock-Jackson, Hui Li, Lin Wu, Lin Zhang, Lei Gu, Jiaxi Wang, Min Guan, Jiang Chang
The ultimate goals of pond fertilization in fish aquaculture, whether raising fingerlings for stocking or growing fish for harvesting, are to increase growth rates and to get higher production in terms of number of surviving fish and weight of those fish (McLarney 1998). Pond fertilization is meant to achieve these goals by supplementing the provision of nutrients needed for bacterial and algal growth and hence zooplankton and benthos production. Bacteria, algae, and zooplankton form the basis of the food web structure necessary to support growth in fish that are planktonic feeders during larval and juvenile stages of growth or as adults (Wu et al. 1997). Although aquaculturists generally agree on the goals of increasing fish growth rate and production through fertilization (often in combination with feed supplementation), there is little real consensus on what type of fertilization regimen is best (Mazid et al. 1997). Low nitrogen-to-phosphorus ratios (N:P) in the fertilization regimen can encourage the growth of toxic cyanobacteria (bluegreen algae). Furthermore, concern is increasing over the negative effects of nutrient-rich discharges from aquaculture ponds on the environment in general (Tucker et al. 1996).
Aquaculture fertilization strategies typically involve adding organic (natural) fertilizers, inorganic (synthetic) fertilizers, or some combination of the two to ponds on a regular basis. In many cases, a fertilization regimen results from tradition or common usage without regard for the nitrogen and phosphorus content of the pond and whether the amounts of these elements in the fertilizer are of the appropriate amounts or ratios. Nitrogen and phosphorus contents are especially difficult to control with the organic fertilization practices that dominate in carp polyculture because hay, bran, and manure nutrients vary depending on the plant source or animal source (and the animal’s feed; Culver 1991), and release rates of individual nutrient elements from organic materials are not constant over time.