Pollutionary effects of waste discharges from aquatic farms
In order to quantify and compare the pollutionary effect of waste discharges from large marine farms in Nordic countries, the Norwe-gian Institute of Water Research (NIVA) recently surveyed waste discharges from salmonid cage farms in Norway and found that production of about 290000 tonnes of salmonids in coastal cage culture in 1998 has led to a feed-based pollution of 4255tons of P and 20286tons of N into the environment of produced fish (Bergheim, 2000). This annual total load of nitrogen and phosphorus is not very high in comparison with the total load of these elements in the seawater (Hikanson et al., 1988). The load of nitrogen derived from agriculture, industries and waste water treatment in Denmark alone was estimated to be around 460000tons per year. The only logical reason for alarm about environmental degradation as a result of expansion and intensification is that it can cause appreciable increases in its pollutive effects. Being a new and emerging industry, its potential is greatly overrated, though social or political considerations may see an urgency in preventing its expansionIrrespective of how aquaculture compares with other sources of negative impacts, aquaculture development itself will be affected adversely if technologies adopted degrade the environment, as has been demonstrated in the collapse of shrimp farms or the pen culture of milkfish and tilapia in certain areas. Water quality can seldom be maintained economically in commercial farms if natural sources are polluted and the environmental integrity of the area is challenged.