Production of farmed fish and shellfish currently adds to net global fish supplies, although many types of aquaculture result in a net loss of fish. Rapid growth in this net-loss sector is severely limiting the potential contribution of aquaculture to future world food supplies.
The benefits of aquaculture, and indeed the potential growth of the industry itself, are diminished by escalating production of species fed carnivorous diets and by aquaculture practices that lead to coastal habitat destruction, biological pollution, and discharge of untreated fish wastes into some of the world’s most diverse and productive marine habitats.
Continued expansion of aquaculture will require healthy coastal and freshwater ecosystems.
Without clear recognition by the industry of its dependence on natural ecosystems, aquaculture is unlikely to develop to its full potential or continue to supplement ocean fisheries. We therefore suggest that governments and development agencies, as well as the aquaculture industry and its trade organizations, adopt four major priorities:
- expansion of the farming of non-carnivorous fish;
- reduction of fish meal and fish oil inputs in feed;
- development of integrated farming systems that use multiple species to reduce costs and wastes and increase productivity;
- promotion of environmentally sound aquaculture practices and resource 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.
Globally, 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 being 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 freshwater 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 international 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 scientific 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 priority in the aquaculture industry.
Efforts to develop substitutes for fish-derived feed ingredients are now focused on commodities such as oil seeds (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 aquaculture feeds, especially for carnivorous fishes, because vegetable 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 freshwater fish diets is technically possible since the n-3 fatty acids 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 vegetable oil in aquaculture feeds may also affect the fatty acid profile and thus flavor and marketability of the fish to consumers. 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 humans, including mollusks and other types of seafood, and research is underway to increase the n-3 fatty acid content in poultry products and in oil seeds 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.
Information Sourced From:
