Fish farming is very efficient in terms of the conversion of protein, which means an important ecological advantage in light of the sustainability of fish feed resources, says a report in the CONSENSUS brochure: 'Towards Sustainable Aquaculture in Europe'.

One of the most-frequently cited issues with the sustainable development of aquaculture is the capture of other fish as raw material to be used as fish feed in the form of fish meal and fish oil. It is seen as an issue because a food production sector is in part relying on a capture fishery for the supply of raw materials for the production of aquaculture feed.

Typically, these other fish species are small, oil-rich, bony pelagic fish that are not normally used for direct human consumption. Two decades ago, the majority of fish meal and oil was used to make feeds for land animal production. At present, over 50 percent of fishmeal and over 80 percent of fish oil is used for aquaculture.

If aquaculture is to fill the gap in demand for seafood, this raises important sustainability issues as to the availability of sufficient feed supply. This is particularly relevant given the fact that fishmeal and fish oil production has been, and is likely to remain, relatively constant at around 6 million and 0.9 million tonnes per year, respectively.

However, as the demand for fishmeal and fish oil in aquaculture has increased, so the price has risen. This has driven both terrestrial agriculture and aquaculture to seek nutritional alternatives to fishmeal and fish oil. This is an on-going process and estimates made by the International Fishmeal & Fish oil Organisation (IFFO) show that the growth of aquaculture and the substitution of fishmeal and fish oil can continue together. The IFFO has started to produce datasheets on fisheries for fish meal and fish oil and these are available at the IFFO web site.

Conversion of caught wild fish to farmed fish

It has been noted that certain types of fish, particularly salmon, are net consumers, requiring in the region of 3 kg of wild fish as feed to produce 1 kg of farmed fish. While it is true that growing high-quality salmon requires considerable amounts of fishmeal and oil, improved technology in fishmeal and oil production as well as better feeding practices on farms have reduced the ratio over time.

Salmon are an exception, because their diets require large amounts of fish oil. For aquaculture overall, the ratio is now well below one: less fish is used for feed than is produced at farms. For carnivorous species, the ratio is still decreasing and expected to reach 1.0 around 2012 (IFFO).

These figures do not include recent gains thanks to the recovery of meal and oil from aquaculture waste. Increasingly in Europe, waste from aquaculture is collected and processed, redirecting around 50 percent of the harvested weight to valuable products.

It should also be noted that wild carnivorous fish also need food. It is estimated that it takes 10 kg of forage fish to produce 1 kg of salmon caught in the wild. If by-catch values are added to the equation, another 5 kg of forage fish has to be added. Hence, even a 3 to 1 ratio for farmed salmon would be significantly better than a 10-15 to 1 ratio of salmon caught in the wild.

Efficiency of food conversion in farmed fish

The ‘food conversion ratio’ (FCR) is defined as the weight of food that is required to produce one kilogram of fish. In the early days of aquaculture, farmed fish were fed with whole ‘trash’ fish and FCRs were more than 20 to 1. Through the years, the ratio has dramatically declined. With the advent of dry, pelletised feeds and modern extrusion technologies, FCR levels are now almost 1 to 1. Certain trout and salmon farms achieve an FCR of less than 1:1, making them far more efficient converters of marine protein than their wild counterparts.

As fish feeds represent an increasingly high share of total production cost, fish farmers have every interest in using feeds as effectively as possible, thereby also reducing the potential environmental impacts of non-consumed feeds. Overfeeding or underfeeding would increase the FCR. Therefore, many farms are equipped with underwater surveillance and monitoring systems as well as devices controlling the supply and delivery of feed.

December 2008

the Fish Site Editor

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