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Effects of Aquaculture on Effects of Aquaculture on Effects of Aquaculture on World Fish Supplies ish Supplies ish Supplies I Published by the Ecological Society of America Number 8, Winter 2001 ssues in Ecology
Issues in Ecology Number 8 Winter 2001 Effects of Aquaculture on World Fish Supplies SUMMARY Global production of farmed fish,shrimp,clams,and oysters more than doubled in weight and value during the 1990s while landings of wild-caught fish remained level.Many people look to this growth in aquaculture to relieve pressure on ocean fish stocks,most of which are now fished at or beyond capacity,and to allow wild populations to recover.Production of farmed fish and shellfish does increase world fish supplies.Yet by using increasing amounts of wild- caught fish to feed farmed shrimp and salmon,and even to fortify the feed of herbivorous fish such as carp,some sectors of the aquaculture industry are actually increasing the pressure on ocean fish populations. The available scientific evidence indicates that some types of aquaculture are on a destructive path that poses a threat not only to wild fish stocks but also to the industry's own long-term potential.One of the most disturbing trends is the rapid expansion and intensification of shrimp and salmon farming and culture of other high-value carnivorous marine fish such as cod,seabass,and tuna.Production of a single kilogram of these species typically uses two to five kilograms of wild-caught fish processed into fish meal and fish oil for feed. Besides this direct impact on wild fish stocks,some aquaculture as currently practiced degrades the marine environment and diminishes the ecological life support services it provides to fish,marine mammals,and seabirds,as well as humans.These impacts include Destruction of hundreds of thousands of hectares of mangrove forests and coastal wetlands for construction of aquaculture facilities Use of wild-caught rather than hatchery-reared finfish or shellfish fry to stock captive operations,a practice that often leads to a high rate of discarded bycatch of other species Heavy fishing pressure on small ocean fish such as anchovies for use as fish meal,which can deplete food for wild fish such as cod,as well as seals and seabirds Transport of fish diseases into new waters and escapes of non-native fish that may hybridize or compete with native wild fish As aquaculture production continues to expand and intensify,both its reliance and its impact on ocean fisheries are likely to increase.The balance between farmed and wild-caught fish,as well as the total supply of fish available for human consumption,will depend on future trends in aquaculture practices.If the goal of aquaculture is to produce more fish for consumers than can be produced naturally,then it will become increasingly counterproductive to farm carnivores that must be fed large amounts of wild-caught fish that form the foundation of the ocean food chain.Indeed,non-carnivorous species such as marine mollusks and carps account for most of the current net gain in world fish supplies from aquaculture. Without clear recognition of its dependence on natural ecosystems,the aquaculture industry is unlikely to develop to its full potential or continue to supplement ocean fisheries.We recommend the adoption of four priority goals for aquaculture: Encourage farming of species lower on the food web-that is,fish with herbivorous or omnivorous diets or filter feeders such as oysters Improve feed management and efficiency in industrial aquaculture systems and develop substitutes for fish- derived feed ingredients Develop integrated fish farming systems that use multiple species to reduce costs and wastes while increasing productivity Promote environmentally sound aquaculture practices and resource management Governments have a key role to play in developing regulations to protect coastal ecosystems and in reexamining subsidies to unsustainable marine fisheries.Development agencies are strategically placed to help in developing and implementing sustainable production practices and in financing otherwise economically and socially unattainable reforms in developing countries.If public and private interests act jointly to reduce the environmental costs generated by fish farm- ing,present unsustainable trends can be reversed and aquaculture can make an increasingly positive contribution to global fish supplies. Cover(clockwise from top):shrimp ponds in Honduras(courtesy CODDEFFAGOLF):basket of milkfish (J.Primavera);harvesting catfish in Mississippi(K.Hammond,courtesy USDA)
1 Issues in Ecology Number 8 Winter 2001 Effects of Aquaculture on World Fish Supplies ish Supplies SUMMARY Global production of farmed fish, shrimp, clams, and oysters more than doubled in weight and value during the 1990s while landings of wild-caught fish remained level. Many people look to this growth in aquaculture to relieve pressure on ocean fish stocks, most of which are now fished at or beyond capacity, and to allow wild populations to recover. Production of farmed fish and shellfish does increase world fish supplies. Yet by using increasing amounts of wildcaught fish to feed farmed shrimp and salmon, and even to fortify the feed of herbivorous fish such as carp, some sectors of the aquaculture industry are actually increasing the pressure on ocean fish populations. The available scientific evidence indicates that some types of aquaculture are on a destructive path that poses a threat not only to wild fish stocks but also to the industry’s own long-term potential. One of the most disturbing trends is the rapid expansion and intensification of shrimp and salmon farming and culture of other high-value carnivorous marine fish such as cod, seabass, and tuna. Production of a single kilogram of these species typically uses two to five kilograms of wild-caught fish processed into fish meal and fish oil for feed. Besides this direct impact on wild fish stocks, some aquaculture as currently practiced degrades the marine environment and diminishes the ecological life support services it provides to fish, marine mammals, and seabirds, as well as humans. These impacts include • Destruction of hundreds of thousands of hectares of mangrove forests and coastal wetlands for construction of aquaculture facilities • Use of wild-caught rather than hatchery-reared finfish or shellfish fry to stock captive operations, a practice that often leads to a high rate of discarded bycatch of other species • Heavy fishing pressure on small ocean fish such as anchovies for use as fish meal, which can deplete food for wild fish such as cod, as well as seals and seabirds • Transport of fish diseases into new waters and escapes of non-native fish that may hybridize or compete with native wild fish As aquaculture production continues to expand and intensify, both its reliance and its impact on ocean fisheries are likely to increase. The balance between farmed and wild-caught fish, as well as the total supply of fish available for human consumption, will depend on future trends in aquaculture practices. If the goal of aquaculture is to produce more fish for consumers than can be produced naturally, then it will become increasingly counterproductive to farm carnivores that must be fed large amounts of wild-caught fish that form the foundation of the ocean food chain. Indeed, non-carnivorous species such as marine mollusks and carps account for most of the current net gain in world fish supplies from aquaculture. Without clear recognition of its dependence on natural ecosystems, the aquaculture industry is unlikely to develop to its full potential or continue to supplement ocean fisheries. We recommend the adoption of four priority goals for aquaculture: • Encourage farming of species lower on the food web – that is, fish with herbivorous or omnivorous diets or filter feeders such as oysters • Improve feed management and efficiency in industrial aquaculture systems and develop substitutes for fishderived feed ingredients • Develop integrated fish farming systems that use multiple species to reduce costs and wastes while increasing productivity • Promote environmentally sound aquaculture practices and resource management Governments have a key role to play in developing regulations to protect coastal ecosystems and in reexamining subsidies to unsustainable marine fisheries. Development agencies are strategically placed to help in developing and implementing sustainable production practices and in financing otherwise economically and socially unattainable reforms in developing countries. If public and private interests act jointly to reduce the environmental costs generated by fish farming, present unsustainable trends can be reversed and aquaculture can make an increasingly positive contribution to global fish supplies. Cover (clockwise from top): shrimp ponds in Honduras (courtesy CODDEFFAGOLF); basket of milkfish (J. Primavera); harvesting catfish in Mississippi (K. Hammond, courtesy USDA)
Issues in Ecology Number 8 Winter 2001 Effects of Aquaculture on World Fish Supplies by Rosamond L.Naylor,Rebecca J.Goldburg,Jurgenne Primavera,Nils Kautsky,Malcolm C.M.Beveridge, Jason Clay,Carl Folke,Jane Lubchenco,Harold Mooney,and Max Troell INTRODUCTION oil for use in manufacturing feed for livestock and farmed fish.Between 1986 and 1997,four of the top five,and Global production of farmed fish and shellfish has eight of the top 20 wild species harvested from the ocean more than doubled in weight and value during the past 15 were small fishes used in production of animal feed:ancho- years,growing from 10 million metric tons or megatons(Mt) veta,Chilean jack mackerel,Atlantic herring,chub mack- in the late 1980s to 29 Mt in 1997.Meanwhile,harvests of erel,Japanese anchovy,round sardinella,Atlantic mackerel, ocean fish have remained at around 85 to 95 Mt,and there and European anchovy. is wide acknowledgment that most wild fish stocks are either As aquaculture production continues to increase and over-fished or fished at maximum capacity.Today aquaculture intensify,both its reliance and impact on ocean fisheries are -the farming of fish,shrimp,clams,and oysters-supplies likely to expand even further.The future balance between more than one-fourth of all fish that humans eat.Many farmed and wild-caught fish,the total supply of fish avail- people believe continued growth in aquaculture will relieve able for human consumption,and the very health of the pressure on deteriorating wild fish stocks,allowing their marine environment will depend on trends in aquaculture prac- populations to recover while supplying an ever-increasing tices. demand for protein to nourish a growing human population. Current trends in the aquaculture industry,however, AQUACULTURE IS A DIVERSE ACTIVITY do not support that belief.As practiced today,aquaculture is a mixed blessing for the sustainability of ocean fisheries. Three-fourths of global aquaculture production by The diversity of production systems leads to an underlying weight involves finfish and shellfish;the other fourth is sea- paradox:aquaculture is a possible solution,but also a con- weed.Worldwide,more than 220 species of finfish and shell- tributing factor,to the collapse of fisheries stocks worldwide. fish are farmed.The range of species includes giant clams The farming of carnivorous species such as salmon that obtain most of their nourishment from symbiotic algae, and shrimp,for example,requires vast quantities of wild-caught mussels that filter plankton from the water,carps that largely fish to feed confined stocks-indeed,the norm is that two graze on plants,and salmon that prey on smaller fish(Figure to five kilograms of wild fish biomass are required to produce 1).Typically,the farmed species are enclosed in a secure a single kilogram of these high-market-value species.Con- system such as a pond or floating pen in which they can be fining large numbers of fish in coastal waters,especially in raised under suitable conditions,sheltered from predators and mangroves and wetlands,can also degrade the marine envi- competitors,and sometimes fed and medicated with antibi- ronment and threaten wild species by destroying nursery otics and other drugs.As the intensity of an aquaculture habitat,generating large quantities of nutrients and other operation increases,fish are confined at higher densities,sup- wastes,importing diseases that can spread to wild fish,or plied with all nutritional requirements,and managed more allowing exotic species to escape and thus compete or hy- bridize with wild fish. In contrast,the farming of species such as carp and tilapia that can eat aquatic plants,or oysters,clams,and mussels that filter plankton from the water,can make a large contribution to global fish supplies and food security.How- ever,the trend toward industrial-scale production of carp and other herbivores-and omnivores such as tilapia,cat- fish,and some varieties of shrimp-has led to increasing use of manufactured feed that incorporates fish meal and fish oil. Despite the surge in production of farmed fish,the tonnage of wild fish harvested has not declined.Moreover, as catches of large,valuable carnivorous fish such as cod and haddock have decreased,there has been a gradual shift to Figure 1-Salmon are farmed in floating ponds where harvest of smaller,less valuable species such as anchovy- they can be raised under managed conditions.(Photo:G. species destined,in fact,to be ground into fish meal or fish Daigle,Multi Images,Inc)
2 Issues in Ecology Number 8 Winter 2001 Effects of Aquaculture on World Fish Supplies ish Supplies by Rosamond L. Naylor, Rebecca J. Goldburg, Jurgenne Primavera, Nils Kautsky, Malcolm C. M. Beveridge, Jason Clay, Carl Folke, Jane Lubchenco, Harold Mooney, and Max Troell Figure 1 — Salmon are farmed in floating ponds where they can be raised under managed conditions. (Photo: G. Daigle, Multi Images, Inc). INTRODUCTION Global production of farmed fish and shellfish has more than doubled in weight and value during the past 15 years, growing from 10 million metric tons or megatons (Mt) in the late 1980s to 29 Mt in 1997. Meanwhile, harvests of ocean fish have remained at around 85 to 95 Mt, and there is wide acknowledgment that most wild fish stocks are either over-fished or fished at maximum capacity. Today aquaculture — the farming of fish, shrimp, clams, and oysters — supplies more than one-fourth of all fish that humans eat. Many people believe continued growth in aquaculture will relieve pressure on deteriorating wild fish stocks, allowing their populations to recover while supplying an ever-increasing demand for protein to nourish a growing human population. Current trends in the aquaculture industry, however, do not support that belief. As practiced today, aquaculture is a mixed blessing for the sustainability of ocean fisheries. The diversity of production systems leads to an underlying paradox: aquaculture is a possible solution, but also a contributing factor, to the collapse of fisheries stocks worldwide. The farming of carnivorous species such as salmon and shrimp, for example, requires vast quantities of wild-caught fish to feed confined stocks — indeed, the norm is that two to five kilograms of wild fish biomass are required to produce a single kilogram of these high-market-value species. Confining large numbers of fish in coastal waters, especially in mangroves and wetlands, can also degrade the marine environment and threaten wild species by destroying nursery habitat, generating large quantities of nutrients and other wastes, importing diseases that can spread to wild fish, or allowing exotic species to escape and thus compete or hybridize with wild fish. In contrast, the farming of species such as carp and tilapia that can eat aquatic plants, or oysters, clams, and mussels that filter plankton from the water, can make a large contribution to global fish supplies and food security. However, the trend toward industrial-scale production of carp and other herbivores — and omnivores such as tilapia, catfish, and some varieties of shrimp — has led to increasing use of manufactured feed that incorporates fish meal and fish oil. Despite the surge in production of farmed fish, the tonnage of wild fish harvested has not declined. Moreover, as catches of large, valuable carnivorous fish such as cod and haddock have decreased, there has been a gradual shift to harvest of smaller, less valuable species such as anchovy — species destined, in fact, to be ground into fish meal or fish oil for use in manufacturing feed for livestock and farmed fish. Between 1986 and 1997, four of the top five, and eight of the top 20 wild species harvested from the ocean were small fishes used in production of animal feed: anchoveta, Chilean jack mackerel, Atlantic herring, chub mackerel, Japanese anchovy, round sardinella, Atlantic mackerel, and European anchovy. As aquaculture production continues to increase and intensify, both its reliance and impact on ocean fisheries are likely to expand even further. The future balance between farmed and wild-caught fish, the total supply of fish available for human consumption, and the very health of the marine environment will depend on trends in aquaculture practices. AQUACULTURE IS A DIVERSE ACTIVITY Three-fourths of global aquaculture production by weight involves finfish and shellfish; the other fourth is seaweed. Worldwide, more than 220 species of finfish and shellfish are farmed. The range of species includes giant clams that obtain most of their nourishment from symbiotic algae, mussels that filter plankton from the water, carps that largely graze on plants, and salmon that prey on smaller fish (Figure 1). Typically, the farmed species are enclosed in a secure system such as a pond or floating pen in which they can be raised under suitable conditions, sheltered from predators and competitors, and sometimes fed and medicated with antibiotics and other drugs. As the intensity of an aquaculture operation increases, fish are confined at higher densities, supplied with all nutritional requirements, and managed more
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. (Photos: 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 intensity of culture practices and their impacts on marine ecosystems vary widely (Figure 2). Clams, oysters, and other mollusks are generally farmed along coastlines, with wildcaught 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 particles 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 agricultural 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 formulated feeds. In the past decade, two distinct sectors have emerged within this diverse industry. The first includes commercial farms that rely on intensive and semiintensive methods to produce commodities for regional or global markets. The second encompasses family and cooperative farms that rely on less intensive practices to produce low-value species for household subsistence or local markets. The line between these sectors is growing more blurred, however. In China and other parts of Asia, for example, many small-scale farming operations are intensifying as land and water resources become increasingly scarce and valuable. Asia produces roughly 90 percent of global aquaculture output, and China alone contributes more than twothirds of the total. Although Europe, North America, and Japan together produce just over one-tenth of the global total, these regions consume the bulk of farmed seafood that is traded internationally. Various species of carp dominate the tonnage of farmed fish produced worldwide, and carp production for local or regional use by relatively lowincome households has increased dramatically in Asia (mainly China). In contrast, increased volumes of salmon, shrimp, and other high-value species are marketed mainly in industrialized countries. Farmed output and markets for other lowervalue 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 systems 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 traditional aquaculture systems use little or no fish meal or fish oil, although operators often add nutrient-rich materials such as crop wastes to the water 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 carnivorous fish and shrimp. These two ingredients supply essential amino acids (that is, lysine and methionine) that are deficient
Issues in Ecology Winter 2001 Marine finfish .16 Fel Marine shrimp Salmon Trout Tilapla Carp (fed) Mollusks TOTAL ratlo of wild fsh used for fshmeal to farmed fish produced Figure 3 Wild fish inputs used in feeds for the ten types of fish and shellfish most commoy farmed in1997 presente ratio of wild fish used for farmed fish produce using compound amount of v sed in compound t that her th arp speci d catla)are no ds a not included here. are filte ed compound in plant proteins and fatty acids (eicosapentaenoic acid ifpa marine fish such as flounder.halibut.sole.cod.hake.had and docosahexaenoic acid [DHA],known as n-3 fatty acids) dock,redfish,seabass,congers,tuna,bonito,and billfish not present in vegetable oils.The fish oil and protein also Many salmon and shrimp operations use roughly three kilo provide energy,which is important because fish tend to be grams of fish biomass for each one produced (Figure 4). poor at using carbohydrates for enerqy. Only three of the ten types of fish most commonl All fish,whether omnivorous,herbivorous,or farmed. catfish.milkfish.and carp-use less fish as inputs carnivorous,require about the same quantity of dietary than is ultimately harvested.(Marine mollusks and many protein per kilogram. But freshwater herbivores and filter-feeding carp are not fed compound feeds at all.) omnivores such as carp,tilapia,and catfish are better than Aquaculture is not the world's largest consumer of carnivores at using plant-based proteins and oils,and fish meal.That distinction belongs to the poultry and swine consequently,they need only minimal quantities of fish mea industries. Aquaculture,however,has the fastest growing to supply essential amino acids.Nevertheless,compound feeds demand for fish meal and fish oil. Its share of fish meal sup for tilapia er omnivorous fish often contain about 15 plies rose from o pe rcent in 1988 to 17 percent in 199 percent me mu mor than required over-formulat and 33 percenti 99 fish than in poultry and atio dietary requirements for particular fish age o on ture fee high leve of fish meal and fish y us ake s to nly a fe ed spe spe Fo of ten type m of carnivorous h can use up to of wild fish 1 o kilo of wild fish ired for kilograms farmed fish production rea culture proponents arg ethat even it farmed fish nroduced usin re 2) The s more wild fish biomass thar highest inputs of wild-caught fish more than five kilo is ultimately harvested.it is still more efficient than the mak grams for each kilogram produced are used in raising ing of big fish from little fish in the wild.n other words.ever
4 Issues in Ecology Number 8 Winter 2001 Figure 3 — Wild fish inputs used in feeds for the ten types of fish and shellfish most commonly farmed in 1997 presented as the ratio of wild fish used for fishmeal to farmed fish produced using compound feeds. In calculating the amount of wild fish used in compound feeds, we assumed a 5:1 conversion rate of fish to fishmeal and that one-sixteenth of fishmeal is obtained from processing by-products. 1 Marine finfish (other than salmon, which is listed separately because of its market significance) include flounder, halibut, sole, cod, hake, haddock, redfish, seabass, congers, tuna, bonito, and billfish. 2 Fed carp refers to carp species that are sometimes fed compound feeds. Filterfeeding carp (silver carp, bighead carp, and catla) are not fed compound feeds and are not included here. 3Mollusks are filter-feeders and are not fed compound feeds. 5.16 4.69 2.81 3.16 2.46 1.41 0.94 0.84 0.75 1.90 Marine finfish1 Eel Marine shrimp Salmon Trout Tilapia Catfish Carp (fed) Carp (fed)2 Mollusks3 TOTAL Milkfish Based on Table 2 of Naylor et al. (2000). ratio of wild fish used for fishmeal to farmed fish produced in plant proteins and fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA], known as n-3 fatty acids) not present in vegetable oils. The fish oil and protein also provide energy, which is important because fish tend to be poor at using carbohydrates for energy. All fish, whether omnivorous, herbivorous, or carnivorous, require about the same quantity of dietary protein per kilogram. But freshwater herbivores and omnivores such as carp, tilapia, and catfish are better than carnivores at using plant-based proteins and oils, and consequently, they need only minimal quantities of fish meal to supply essential amino acids. Nevertheless, compound feeds for tilapia and other omnivorous fish often contain about 15 percent fish meal — much more than required. Indeed, manufacturers often over-formulate feeds, in part because information on the dietary requirements for particular fish species is inadequate. Because of these high levels of fish meal and fish oil in aquaculture feeds, it takes more fish biomass to raise some farmed species than those species produce. For the ten types of fish most commonly farmed, for instance, an average of 1.9 kilograms of wild fish are required for every kilogram of farmed fish produced using compound feeds (Figure 3). The highest inputs of wild-caught fish — more than five kilograms for each kilogram produced — are used in raising marine fish such as flounder, halibut, sole, cod, hake, haddock, redfish, seabass, congers, tuna, bonito, and billfish. Many salmon and shrimp operations use roughly three kilograms of fish biomass for each one produced (Figure 4). Only three of the ten types of fish most commonly farmed — catfish, milkfish, and carp — use less fish as inputs than is ultimately harvested. (Marine mollusks and many filter-feeding carp are not fed compound feeds at all.) Aquaculture is not the world’s largest consumer of fish meal. That distinction belongs to the poultry and swine industries. Aquaculture, however, has the fastest growing demand for fish meal and fish oil. Its share of fish meal supplies rose from 10 percent in 1988 to 17 percent in 1994 and 33 percent in 1997. Also, the proportion of fish meal in aquaculture feeds is much higher than in poultry and livestock feeds, which contain an average of only 2 to 3 percent fish meal as a protein supplement. The production of a kilogram of pork or poultry typically uses large amounts of plant proteins, but only a few hundred grams of fish, whereas production of a kilogram of carnivorous fish can use up to five kilograms of wild fish. Some aquaculture proponents argue that even if farmed fish production requires more wild fish biomass than is ultimately harvested, it is still more efficient than the making of big fish from little fish in the wild. In other words, even