Fish oil and fishmeal from wild fish are extensively used in fish farming (also known as aquaculture) as a foodstuff for the farmed fish. But ironically, production of these fish products is also depleting the oceans of some species of forage fish, i.e. fish that are typically eaten by other fish and other predators higher up the food chain.
Globally, fish farming now accounts for 68% and 88% of fish oil and fishmeal production.
Alice Chiu from Stanford University, together with her colleagues from the US, Canada, Norway and Australia, studied trends in fish oil and fishmeal use in industrial aquafeeds between 1995 and 2007. Her team found that the use of fish oil in aquaculture feeds has a much higher impact on forage fisheries than the use of fishmeal.
Forage fish, such as herrings, sardines, menhaden, sprats and anchovies, are often a vital part of oceanic food webs, supporting a number of predators such as larger fish, marine mammals and seabirds. This means that their removal from the food web for fish farming can have a large impact on oceanic ecosystems. In addition, most such fisheries are fully exploited, overexploited or recovering from overexploitation.
Europe currently uses around half the world's production of fish oil, which is used most heavily in salmon farming.
"As consumers increasingly seek out heart-healthy omega-3 oils, elevated demand for fish oil could cause increased pressure on marine fisheries," says Chiu. The maintenance of high omega-3 oil levels in farmed salmon requires a relatively high use of fish oil in their feed, although research into alternatives, such as the plant oil stearidonic acid, is underway.
If fish farming is to continue to grow, alternatives to fish oil and fishmeal will have to be found. Already, algal meals and oils, plant proteins and oils, and seafood and animal processing by-products are sometimes used. But these all have their own ecological, technological and economic problems and challenges, so more research is needed to deal with these challenges.
In the short-term, strategies can be adopted to conserve fishmeal and fish oil resources. These include blending non-fish feed ingredients to satisfy fish nutritional requirements and reserving the use of fish oil for the final feeding stages of the fish lifecycle, so that the health benefits of the oil are retained in the final product.