Resource use and waste production at a semi-intensive, black tiger prawn Penaeus monodon farm.

摘要

A study of resource use and waste production was conducted at the Aqualma shrimp farm in Madagascar. This farm has 685 ha of grow-out ponds where black tiger prawn Peneaus monodon are produced by semi-intensive production techniques. The farm has consistently produced around 3,000 mt/year since it began operations more than 10 years ago.; Three typical production ponds, each roughly 10-ha in area and slightly above 1 m average depth, were selected for measurement of all management inputs and outputs. These budgets allowed calculation of amounts of nutrients applied via the water supply source, and in fertilizers and feeds as well as quantities of nutrients assimilated by the ponds or discharged in effluents. This study revealed that effluents discharged during a single crop contributed 433 kg nitrogen, 288 kg phosphorus, 3,967 kg organic carbon, and 7,994 kg 5-day biochemical oxygen demand (BOD5) per crop. Based on these estimates, the annual discharge of the farm was 65,702 kg nitrogen, 43,704 kg phosphorus, 601,293 kg organic carbon, and 1,211,628 kg BOD5. Although these are large amount of unused nutrients, the Mahajamba Bay that receives the farm effluents has a large volume (4.8 x 109 m3). The total annual quantities of effluent nutrients, if introduced in a single dose and mixed thoroughly into the bay, would cause concentration increases of 0.0136 mg/L nitrogen, 0.0091 mg/L phosphorus, 0.125 mg/L organic carbon, and 0.252 mg/L BOD5. The daily increase would be too small to measure. Of course, the bay assimilates wastes by natural processes, and wastes are flushed out by tidal action and freshwater flow. It seems unlikely that the farm is a serious pollution threat to the bay.; Phosphorus not discharged in effluent was adsorbed by bottom soil causing an increase in soil phosphorus concentration in the upper 10-cm layer of the bottom. Physical, chemical, and biological processes in ponds converted much of the nitrogen and organic carbon to gaseous form (ammonia, nitrogen, carbon dioxide, and methane). The increases in soil nitrogen and soil carbon during the crop were small.; Resource use and waste generation by the farm were assessed per tonne of shrimp production. The total land required for the production of 1 tonne of shrimp was 0.96 ha, including grow-out area, land for farm infrastructure, and land for producing plant meals for feed. The production of 1 tonne of shrimp required 2.067 tonnes of feed containing 0.908 tonne of crude protein (143.5 kg nitrogen), and 0.672 tonne fish meal. About 3.024 tonnes wet weight of marine fish were used to make the fish meal needed in feed for 1 tonne of shrimp. Water use was 90,855 m3/tonne, and the energy use for pumping this water into the farm was estimated to be 868.8 kW·hr/tonne of shrimp produced. Nutrient inputs in feed and fertilizer were 163.2 kg nitrogen/tonne and 31.8 kg phosphorus/tonne. The percentage recovery of these two nutrients in shrimp was 18.9% for nitrogen and 8.2% for phosphorus. Only 3.7% of total organic carbon input to ponds was recovered in shrimp. The amount of liming material applied to the ponds was equivalent to 655 kg CaCO3/tonne.; Unused nutrients in the production of one tonne of shrimp were equivalent to the annual waste contribution of 54.1 people for nitrogen, 68.6 people for phosphorus, and 20.6 people for BOD5. The farm, however, produced enough shrimp to supply the average annual consumption of nearly 2,000,000 Americans who eat about 1.54 kg of shrimp per year.