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.
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 wild6. 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.
Replacement of marine protein sources by (terrestrial) plant protein
For various reasons, fishmeal and oil are gradually being replaced by plant proteins in feed that is used in fish farms. Plant proteins can be less costly and they are free of potential contaminants like dioxin, PCB or mercury.
However, fishmeal is an important ingredient in fish feed and can only to a limited extent be replaced by vegetable proteins without reducing feed efficiency and growth. After all, carnivorous or ‘piscivorous fish naturally feed on other fish. The fatty acid composition in the flesh from farmed fish will also reflect the feed composition and inclusion of vegetable oil will reduce the level of omega-3 fatty acids.
Although the introduction of plant protein into the feed can be seen as a way of reducing the sectors dependence on fish meal and fish oil, some have questioned the trend because:
- carnivorous fish do not naturally feed on plants;
- plant proteins may have anti-nutritional effects on fish;
- there is a maximum level of replacement, after which the texture and eating quality
- of the fish is compromised;
- some plant proteins could be derived from GMOs.
Generally speaking, though, marine plants have enormous potential to act as fish feed ingredients. Initial research has confirmed this potential and our knowledge in this area is starting to build.
Decontamination of fish meal and fish oil
Fishmeal and fish oil are produced from fish that may contain contaminants. Various research projects are ongoing to look into the feasibility of de-contaminating fish meal and fish oil. One such project is carried out at the Fiskeriforskning Institute in Norway.
Fish stocks of concern in the northern European industry are sprat and herring from the Baltic Sea, and herring, sprat, sand eel and blue whiting in the North Sea. The differences in dioxin and PCB levels reflect the general pollution levels in the respective fishing areas and will disfavour the North European fishmeal and oil producers in the world market. This is already the case in aquaculture, where most fishmeal is sourced from the southern hemisphere.
The main objective of the project is to develop a new oil extraction process to reduce the persistent organic pollutants level in fishmeal. The research will aim to identity optimal processing conditions with respect to both decontamination efficiency and preservation of fishmeal and oil quality. The new oil extraction process is expected to have several advantages compared to a standard hexane extraction process. This will include the possibility of easy integration in an existing fishmeal processing line, use of a safe and non-flammable extraction medium and lower investment and operation costs.
Do farmed fish contain artificial colouring?
The natural red/orange colour of salmon results from carotenoid pigments, largely astaxanthin in the flesh. Astaxanthin is a potent antioxidant that stimulates the development of healthy fish nervous systems and that enhances the fishs fertility and growth rate. Wild salmon get these carotenoids from feeding on small crustaceans, such as prawns and shrimp. Astaxanthin does not naturally occur in fish feeds and thus must be added. The astaxanthin which is added to feed is identical to the natural pigment.
Food miles
In recent years, there has been increasing emphasis on energy resources needed to ship in food from afar. Although the relationship between transport and overall sustainability can be complex, it can be said that where food supply chains are otherwise identical, reducing food transport improves sustainability.
Therefore, generally speaking, European aquaculture production could be seen as more efficient in terms of "food miles" than imports of the same species from countries far away.
However, there is a food mile issue with the use of fish meal and fish oil produced in the southern hemisphere and used in Europe, although this is itself a trade-off of not using fish meal produced in Europe due to issues of species in recovery (e.g. sandeel and capelin) and contamination of fish meal and oil (e.g. Baltic herring).
However, as stated before, comparisons can be complex, involving differences between food supply systems that often involve trade-offs between a diverse variety of environmental, social and economic factors. The impact of food transport can be offset to some extent if food imported to an area has been produced more sustainably than the food available locally. For example, a case study showed that it can be more sustainable (at least in energy efficiency terms) to import tomatoes from Spain than to produce them in heated greenhouses in the UK outside the summer months.
In the case of fishmeal and fish oil, the worlds largest producers of fishmeal and fish oil are in South America. There, fishmeal and fish oil are mass-produced very efficiently and shipped overseas (already with a reduced water content in the case of fishmeal) to Europe to be used as feed in aquaculture. Surely, this has to compare favourably to using airplanes to import fresh fish from Asia or South America.
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