Environmental issues in integrated agriculture-aquaculture and wastewater-fed fish culture systems
1993
Edwards, P. (Asian Inst. of Technology, P.O. Box 2754, Bangkok 10501 (Thailand). Div. of Agricultural and Food Engineering)
Data are presented from two experimental semi-intensive systems, involving bagged chicken manure supplemented with inorganic fertilizers and clarified sewage effluent: only 15 and 11% of the fertilizer N and 8 and 6% of the fertilizer P, respectively, were removed in harvested fish; only 2 and 6% of the N and 6 and 10% of the P, respectively, were released to the environment on draining the ponds at the end of the experiment; the remaining 83% of the N and 86 and 84% of the P, respectively, "disappeared" within the culture system, and probably most accumulated in the sediments. While 21-53% of the N and 11-28% of the P in feed are removed in harvested fish in the intensive system (with a higher feed nutrient conversion efficiency to fish than the semi-intensive system), the remainder of the nutrients in the feed are voided to the environment continuously throughout the culture cycle. In terms of weight of N and P released to the environment per kg of fish produced, the intensive system is 7-31 and 3-11 times more polluting than the semi intensive system, respectively, depending on the FCR of complete feed. The feeds in the intensive systems are consumed directly by fish, whereas fertilizer nutrients are utilized indirectly through natural feed production in the semi-intensive pond system. However, the nutrient conversion efficiency of the semi-intensive system (with N supplied as fertilizer) is only slightly less than that of the intensive system (with N supplied in the form of feed protein): less than one-tenth the difference that might be expected from the extra step in the food chain in the fertilized system
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