Issues in Ecology Number 8 Winter 2001 heavily.The more intensive the operation,of course,the China).In contrast,increased volumes of salmon,shrimp larger the volume of wastes generated and the greater the and other high-value species are marketed mainly in industr possibilities for the spread of disease. alized countries.Farmed output and markets for other lower From one aquaculture operation to another,the in- value species such as tilapia and milkfish have increased in tensity of culture practices and their impacts on marine eco- both developing and industrialized countries.Most farmed systems vary widely (Figure 2).Clams,oysters,and other mollusks are still consumed locally and regionally in China mollusks are generally farmed along coastlines. with wild and in other developing countries.However.production caught or hatchery-reared seed grown on the sea floor or on certain species for global markets has increased in severa suspended nets,ropes,or other structures. The animals feed developed countries.These species include the Pacific cuppec organic par oyster,blue mussel,New Zealand mussel,and Yesso scallop cages FEEDING FISH TO FISH migrate be en fresh anc supp Many and sem aquaculture sys Carp.catfish.and othe nwater finfis more fish prot odu n coastal n nds of both shrimp and freshwater finfish varies or no fish meal or fish oil.althoug greatly from one operation to anothe operators often add nutrient-rich ma in intensity and in reliance on form torials such a s cron wastes to the wa ter to stimulate owth of algae In the past decade.two distinct othe aturally available orga sectors have emerged within this diverse which the fish feed. industry.The first includes commercial Worldwide,about 80 percent farms that rely on intensive and semi- of carp and 65 percent of tilapia are intensive methods to produce commodi- farmed without the use of moderr ties for regional or global markets.The compound feeds -that is.feed second encompasses family and coop- formulated from multiple ingredients. erative farms that rely on less intensive In China,however,farmed production practices to produce low-value species of carp and other omnivorous species for household subsistence or local mar s intensifying,and new commercial kets.The line between these sectors is eed mills are being developed to serve n this industry.China is also the largest mporter of fish meal in the w rld.Suc ntensive systems,incl creasingly scarce fish are stocked at highe e can be produces cent of global Flaure 2 -Aquaculture is a diverse se com tha activity with a range of species such as of the e total.Alth percentag catfish and tiger prawns.From one one-tenth of the al aquaculture operation to another,the bal total.these regions consume the intensity and impacts vary widely.(Pho- mnivorous fish can also contain lo tos:K.Hammond,courtesy USDA (top) bulk of farmed seafood that is traded and J.Primavera (bottom) ra lvels of protein obtained internationally. from fish and terrestrial animals. Various species of carp domi By contrast.fish meal and fish nate the tonnage of farmed fish produced worldwide,and oil are dominant ingredients in compound feeds for camnivo carp production for local or regional use by relatively low- rous fish and shrimp.These two ingredients supply essential income households has increased dramatically in Asia (mainly amino acids(that is,lysine and methionine)that are deficient 3 Issues in Ecology Number 8 Winter 2001 Figure 2 — Aquaculture is a diverse activity with a range of species such as catfish and tiger prawns. From one aquaculture operation to another, the intensity and impacts vary widely. (Pho￾tos: K. Hammond, courtesy USDA (top) and J. Primavera (bottom). heavily. The more intensive the operation, of course, the larger the volume of wastes generated and the greater the possibilities for the spread of disease. From one aquaculture operation to another, the in￾tensity of culture practices and their impacts on marine eco￾systems vary widely (Figure 2). Clams, oysters, and other mollusks are generally farmed along coastlines, with wild￾caught or hatchery-reared seed grown on the sea floor or on suspended nets, ropes, or other structures. The animals feed entirely on ambient supplies of plankton and organic par￾ticles in the water. Finfish may be farmed in ponds, tanks, or cages. Most marine fish and species such as salmon that migrate between fresh and salt water are reared in floating net cages near shore, and all their nutrition is supplied by formulated feeds. Carp, catfish, and other freshwater finfish are usually grown in ponds, often integrated within agricul￾tural settings. Crustacean farming is dominated by shrimp, which are grown in coastal ponds. Farming of both shrimp and freshwater finfish varies greatly from one operation to another in intensity and in reliance on formu￾lated feeds. In the past decade, two distinct sectors have emerged within this diverse industry. The first includes commercial farms that rely on intensive and semi￾intensive methods to produce commodi￾ties for regional or global markets. The second encompasses family and coop￾erative farms that rely on less intensive practices to produce low-value species for household subsistence or local mar￾kets. The line between these sectors is growing more blurred, however. In China and other parts of Asia, for ex￾ample, many small-scale farming opera￾tions are intensifying as land and wa￾ter resources become increasingly scarce and valuable. Asia produces roughly 90 per￾cent of global aquaculture output, and China alone contributes more than two￾thirds of the total. Although Europe, North America, and Japan together produce just over one-tenth of the glo￾bal total, these regions consume the bulk of farmed seafood that is traded internationally. Various species of carp domi￾nate the tonnage of farmed fish produced worldwide, and carp production for local or regional use by relatively low￾income households has increased dramatically in Asia (mainly China). In contrast, increased volumes of salmon, shrimp, and other high-value species are marketed mainly in industri￾alized countries. Farmed output and markets for other lower￾value species such as tilapia and milkfish have increased in both developing and industrialized countries. Most farmed mollusks are still consumed locally and regionally in China and in other developing countries. However, production of certain species for global markets has increased in several developed countries. These species include the Pacific cupped oyster, blue mussel, New Zealand mussel, and Yesso scallop. FEEDING FISH TO FISH Many intensive and semi-intensive aquaculture sys￾tems use two to five times more fish protein, in the form of fish meal and fish oil, to feed the farmed animals than is produced in the form of farmed fish. By contrast, so-called extensive or tra￾ditional aquaculture systems use little or no fish meal or fish oil, although operators often add nutrient-rich ma￾terials such as crop wastes to the wa￾ter to stimulate growth of algae and other naturally available organisms on which the fish feed. Worldwide, about 80 percent of carp and 65 percent of tilapia are farmed without the use of modern compound feeds – that is, feeds formulated from multiple ingredients. In China, however, farmed production of carp and other omnivorous species is intensifying, and new commercial feed mills are being developed to serve this industry. China is also the largest importer of fish meal in the world. Such intensive systems, including U.S. catfish farms, must rely heavily on added feeds because fish are stocked at higher densities than can be supported by natural food sources. Generally these operations use compound feeds that contain high percentages of protein supplements from soybean meal, cottonseed meal, and peanut meal. But compound feeds for herbivorous and omnivorous fish can also contain low to moderate levels of protein obtained from fish and terrestrial animals. By contrast, fish meal and fish oil are dominant ingredients in compound feeds for carnivo￾rous fish and shrimp. These two ingredients supply essential amino acids (that is, lysine and methionine) that are deficient