Issues in Ecology Number 8 Winter 2001 trade organizations,adopt four major priorities:1)expan- content of some feeds for example feed for salmon-has sion of the farming of non-carnivorous fish:2)reduction of been reduced considerably.albeit largely by substituting fish meal and fish oil inputs in feed:3)development of inte- cheaper fish oil for fish meal Nevertheless.severe barriers grated farming systems that use multiple species to reduce exist to complete replacement of fish meal and fish oil in aquac costs and wastes and increase productivity:and 4)promo- ulture feeds,especially for carnivorous fishes,because veg tion of environmentally sound aquaculture practices and re- etable proteins have inappropriate amino acid balance and source management. poor protein digestibility. We believe more scientific research is also needed on Farming Lower on the Food Web the feed requirements of herbivores and omnivoresin orde toward add ling fish meal an sp diets stituting vegetabl found in nically possible arps and manne ids fish oil are not essen al in the di ent nt glo spe Ho n appear to robus n fish o ent But and marke P0 etableo d st t of fa s that th rat 3 weight,but almost 20er acids in human diets is already too in addition.fish meal and fish oil are increasind gly be alternatives to finfish as sources of atty acids for hu ina added to carn and tilapia feeds to boost mans including mollusks and other 20 especially in Asia where far vstems are inte research is underway to increase the n-3 fatty acid conten a result of the increased scarcity and value of land and f in poultry pr oducts and in oilseeds used for feed. water resources.given the huge volume of farmed carn and A move toward partial substitution of plant and tilapia in Asia,significant increases in the fish meal and fish terrestrial animal proteins for fish proteins now used in feec oil content of feed would place even more pressure on open is widely accepted as necessary within the aquacultur ocean fisheries.resultina in hiaher feed prices as well as harm industry.yet there is disagreement over the urgency of such to marine ecosystems a move.because over-exploitation of ocean fisheries has we believe new initiatives by aovernments and inter negative ecological and social consequences,developing a national donor agencies are needed to further encourage strategy to replace fish meal and fish oil in feeds should be a farming of species lower on the food web- that is.fish with priority for governments and development organizations as nerbivorous diets. At the same time,we believe more scien- well as industry. tific research on the feed requirements of herbivores and omnivores is required to lessen the drive to add fish meal and Integrating Production Systems fish oil to their feeds. The farming of multip polyculture in a single ponc Reducing Fish Meal and Fish Oil in Fish Feed centu he adven of dustrial-scale quac tur ven today,Io The cost of ly cu spe p00 of and shrim 9d53 carp (a meal filte lative to plants ha pa e d arp (az h of fish meal and fish oil could nine the fror thereby reducingc many aquaculture enterprises.For these reasons.research to and wastes while increasing improve feed efficiency in industrial systems is already a pri rated systems can also be used for hiah-value fish ority in the aquaculture industr such as salmon and shrimp in order to reduce waste out ffforts to develop substitutes for fish-derived feed in puts.diversify products.and increase productivity.Some stud gredients are now focused on commodities such as oilseed ies show tha seaweed and mussels arow well in wastewate (especially sovbeans).meat byproducts (such as blood meal from intensive and semi-intensive aquaculture systems,and and bone meal).and microbial proteins.Already the fish meal as a result,reduce nutrient and particulate loads to the envi- 9 Issues in Ecology Number 8 Winter 2001 trade organizations, adopt four major priorities: 1) expan￾sion of the farming of non-carnivorous fish; 2) reduction of fish meal and fish oil inputs in feed; 3) development of inte￾grated farming systems that use multiple species to reduce costs and wastes and increase productivity; and 4) promo￾tion of environmentally sound aquaculture practices and re￾source management. Farming Lower on the Food Web Farmed fish species fed mainly on herbivorous diets account for most of the 19 Mt gain in fish supplies that aquaculture now provides to the world. Carps and marine mollusks make up 75 percent of current global aquaculture output, and tilapia, milkfish, and catfish contribute another 5 percent. But market forces and government policies in many countries favor rapid expansion in production of high￾value, carnivorous species, such as salmon and shrimp. Glo￾bally, these species represent only 5 percent of farmed fish by weight, but almost 20 percent by value. In addition, fish meal and fish oil are increasingly be￾ing added to carp and tilapia feeds to boost weight gain, especially in Asia where farming systems are intensifying as a result of the increased scarcity and value of land and fresh￾water resources. Given the huge volume of farmed carp and tilapia in Asia, significant increases in the fish meal and fish oil content of feed would place even more pressure on open ocean fisheries, resulting in higher feed prices as well as harm to marine ecosystems. We believe new initiatives by governments and inter￾national donor agencies are needed to further encourage farming of species lower on the food web — that is, fish with herbivorous diets. At the same time, we believe more scien￾tific research on the feed requirements of herbivores and omnivores is required to lessen the drive to add fish meal and fish oil to their feeds. Reducing Fish Meal and Fish Oil in Fish Feed The cost of purchasing feed is the largest production expense for commercial aquaculture, including most farming of salmon, other marine finfish, and shrimp. Moreover, the price of fish meal relative to other protein substitutes has risen in real terms in the past few decades and is likely to continue to escalate as demand grows. Increases in the prices of fish meal and fish oil could undermine the profitability of many aquaculture enterprises. For these reasons, research to improve feed efficiency in industrial systems is already a pri￾ority in the aquaculture industry. Efforts to develop substitutes for fish-derived feed in￾gredients are now focused on commodities such as oilseeds (especially soybeans), meat byproducts (such as blood meal and bone meal), and microbial proteins. Already the fish meal content of some feeds — for example, feed for salmon — has been reduced considerably, albeit largely by substituting cheaper fish oil for fish meal. Nevertheless, severe barriers exist to complete replacement of fish meal and fish oil in aquac￾ulture feeds, especially for carnivorous fishes, because veg￾etable proteins have inappropriate amino acid balance and poor protein digestibility. We believe more scientific research is also needed on the feed requirements of herbivores and omnivores in order to reverse the trend toward adding fish meal and fish oil to their feeds. Substituting vegetable oils for fish oils in fresh￾water fish diets is technically possible since the n-3 fatty ac￾ids found in fish oil are not essential in the diets of these species. However, some herbivorous fish appear to have more robust immune systems when fish oil is included in their diet. In addition, substitution of fish oil with cheaper veg￾etable oil in aquaculture feeds may also affect the fatty acid profile and thus flavor and marketability of the fish to con￾sumers. Evidence suggests that the ratio of n-6 to n-3 fatty acids in human diets is already too high. There are, however, alternatives to finfish as sources of n-3 fatty acids for hu￾mans, including mollusks and other types of seafood, and research is underway to increase the n-3 fatty acid content in poultry products and in oilseeds used for feed. A move toward partial substitution of plant and terrestrial animal proteins for fish proteins now used in feed is widely accepted as necessary within the aquaculture industry, yet there is disagreement over the urgency of such a move. Because over-exploitation of ocean fisheries has negative ecological and social consequences, developing a strategy to replace fish meal and fish oil in feeds should be a priority for governments and development organizations as well as industry. Integrating Production Systems The farming of multiple species in a single pond — polyculture — was practiced for centuries before the advent of industrial-scale aquaculture. Even today, four of the most widely cultivated fish species are sometimes produced together in the same ponds in China: silver carp (a phytoplankton filter feeder), grass carp (a herbivore that grazes aquatic plants), common carp (an omnivorous bottom feeder that eats detritus), and bighead carp (a zooplankton filter feeder). This type of system efficiently uses food and water resources from all levels of the pond ecosystem, thereby reducing costs and wastes while increasing productivity. Integrated systems can also be used for high-value fish, such as salmon and shrimp, in order to reduce waste out￾puts, diversify products, and increase productivity. Some stud￾ies show that seaweed and mussels grow well in wastewater from intensive and semi-intensive aquaculture systems, and as a result, reduce nutrient and particulate loads to the envi-