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Risks and Solutions to Feeding Fish with Fish

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Continuous advancements in the science of aquaculture has enabled farmers to produce ever greater varieties of fish. But whilst this allows industries to meet consumer demands, an unquenchable desire for large carnivorous fish is not sustainable, writes Adam Anson, TheFishSite reporter.

Technology has brought about many revelations in aquaculture. Of which, the ability to raise large carnivorous fish such as cod, tuna and salmon is regarded by many as one of the most dramatic. The explosive growth of the salmon industry, which now occupies the largest market of all finfish, would have been unattainable without the aid of aquaculture.

fish to be fed to fish to be fed to people
Image Credit: Oceana

Similarly, the recent collapse of bluefin tuna stocks has not eased human appetite. In Japan, Australia, Canada and Mexico, the solution to this collapse lies in a process called 'tuna fattening'. This involves capturing juvenile bluefin and feeding the voracious carnivore with frozen fish prey until they are large enough to be sold into lucrative sushi and sashimi markets.

Unfortunately, this solution is outbalanced by the weight of the problem that it poses: with dwindling worldwide fish stocks, even the fish that they are fed upon will soon run out. According to figures obtained in Oceana's Hungry Oceans report, an estimated 225,000 metric tonnes of prey fish is thrown into the Mediterranean tuna pens alone each year. The report describes an increasing pattern of ecosystem collapse throughout the oceans, beginning with the demise of even the smallest fish, previously believed to be indestructible.

This same problem applies for all farmed carnivorous fish, which all need to be subsidised from fish oils and fishmeal derived from ocean fish. This, somewhat ironic conundrum, has prompted many to ask how the aquaculture industry can ever hope to become sustainable if it takes more from the oceans by weight than it can produce. Rather than reducing the burden on the ocean's fish, many aquaculture operations are fueled on it.

Fishmeal Uses

Credit: Oceana

Currently one third of all capture fisheries worldwide are reduced into fish meal and oil each year. Of this, Oceana estimate that 81 per cent is destined for the aquaculture industry - the rest goes into pet food and livestock feed, with a small amount destined for human consumption in capsules and health foods.

A smaller percentage of fishmeal is derived from byproducts of fish processing. Within the European Union (EU) it is estimated that in 2002 about 33 per cent of the fishmeal produced in the EU-15 was manufactured from trimmings from food fish processing. Spain, France and Germany all produced 100 per cent of their fishmeal this way. An amount of fishmeal is also derived from unreported or illegal bycatch, but at present no official statistical information is available on this amount.

According to Oceana's report, among farmed fish, salmon consume more fish oil than all other aquaculture operations combined. In 2003, salmon pens alone consumed 51 per cent of world fish oil and 19 per cent of world fishmeal supplies respectively. "For salmon aquaculture, an estimated four to eleven pounds of prey fish are consumed to grow only one pound of farmed salmon," said the report.

Currently feed companies are unable to keep up with demands, which hampers the growth of these new aquaculture industries. But as the demand for fishmeal and fish oils rise so does the price. Unfortunately, there is no available method for raising salmon and tuna without fishmeal and fish oils, so the lucrative market incentives will lead to further overfishing in the oceans. Inevitably, these industries will consume so much that there will be little or nothing left to sustain them. This scenario will bring about the demise of other fish industries and the health of marine creatures in general, prompting many to ask where a solution can be found.

"Compared with other terrestrial animal and plant protein sources, fishmeal is unique in that it is not only an excellent source of high quality animal protein and essential amino acids, but is also a good source of digestible energy, essential minerals and vitamins, and lipids, including the essential polyunsaturated fatty acids," says Albert G.J. Tacon Ph.D., Aquaculture Research Director and author of the report State of Information on Salmon Aquaculture Feed and the Environment.

In his report, which was published by the World Wildlife Fund (WWF), Dr Tacon, says that two thirds of salmon feeds by weight are composed of fishmeal and fish oil. The average fish carnivore - such as eels, salmonids and marine finfish - consume fish feeds which are composed of 35-75 per cent of marine products as a starter, and 20-50 per cent as a grower. Even fish omnivores - such as carp, tilapia and catfish - consume feed composed of 10-25 per cent fishmeal and fish oils as a starter, and 2-15 per cent as a grower.

"The paradoxical situation has emerged that increased aquaculture production leads to increased pressure on wild fish stock"
Extract from the report, Are Dietary Recommendations for the Use of Fish Oils Sustainable?

Whilst the report goes on to say that salmon do not have a specific dietary requirement for fishmeal or fish oils, it also accept that the nutritional profile which most closely resembles their biological and digestive requirements is found within them. Whilst it is possible to replicate the proteins found in fishmeal with others derived from non-marine sources, there has been great difficulty in replicating essential fish oils. Currently, there are no commercial alternatives.

"Complete dietary fishmeal and fish oil replacement in salmonids has not been possible to date for a variety of different factors," says the report. The most important of these being "the higher apparent sensitivity of salmonids to the anti-nutritional factors present within plant meals", and the "higher nutrition skills required to formulate rations to preset available dietary nutrient levels." However, Dr Tacon estimates that it is currently possible for feed manufacturers to reduce up to 70 per cent and 50 per cent of the fishmeal and fish oil content of salmon feeds with alternative proteins and lipids. Dr Tacon believes that this could be partly resolved through the use of plant oils and animal fats.

A different report - Are Dietary Recommendations for the Use of Fish Oils Sustainable?, which was published in the Canadian Medical Association Journal - points to the lack of public awareness concerning the consumption of large, farmed, carnivorous fish. The report suggests that, rather than rectifying this problem with educational campaigns, current public information actually promotes it. The report points to misleading omega 3 health claims, leading to this unsustainable level of fish consumption in human diets.

"Because the aquaculture industry cannot eliminate fishery-derived products such as herring, sardines, anchovies and other edible small fishes from the diet of farmed fish, the paradoxical situation has emerged that increased aquaculture production leads to increased pressure on wild fish stock", says the report. Adding that, on average, it takes "2.5–5 kg of feed fish to make 1 kg of farmed carnivorous fish."

The world needs an alternative source of fishmeal and oils and there may be a solution on the horizon. Major corporations are currently working on genetically modified yeast and plants that could serve as factories for the synthesis of long-chain omega-3 fatty acids, including eicosapentaenoic acid. More recently, a university and non-GMO soybean company developed a sustainable alternative for farmed fish using seaweed oils. The company behind the product says that these microseaweed oils are capable of improving salmon, trout, cod and other farmed fish feeding with omega-3 and 6 fatty acids.

Whilst alternative feed sources will be found at some point in the uncertain future, limited ocean fish stocks cannot last forever. It isn't only consumer interests that are at risk, it is fisheries industries as a whole, both on-land, off-shore and at-sea. The value of the ocean, and all that lies within it, is at stake. For now the fate of these problems rests upon consumer awareness, government action and greater efficiency of what materials currently exist, but the arrival of a truly sustainable alternative to fishmeal and oils is almost certain to herald an aquaculture revelation bigger than any that has come before.

March 2009