Common carp and aquaculture

Aquaculture is the fastest growing animal-food-producing sector with a growth rate from 1970 of around 8.3% per year and with 52.5 million tons (in 2008; 68.3 including aquatic plants) and accounts for almost half of total food fish supply (SOFIA, 2010). Fish oil and fish meal have been traditionally used as ingredients in aqua-feeds for carnivorous fish culture. Fish oil has a high level of the n-3 highly unsaturated fatty acids (n-3 HUFA; 20 and more carbons and 3 and more double bonds), especially eicosapentaenoic (EPA; 20:5n-3), docosapentaenoic (DPA; 22:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), being natural and nutritious for fish as well as for humans. As the aquaculture is expanding, fish meal and fish oil become more expensive and scarce. It consequently creates a high pressure on the aqua-feed producers to replace these ingredients with more sustainable alternatives (Pickova & Morkore, 2007). Generally, vegetable sources of oil and protein are used as “The replacement”. Vegetable oils can replace substantial amount of fish oil in the diets of many fish species without affecting growth and feed efficiency. However, the drawback of these alternatives is the lack of n-3 HUFA and therefore compromising the nutritive value of farmed fish for consumers. Several alternative oil sources, derived from unicellular algae, pelagic organisms or benthic invertebrates containing high amounts of n-3 HUFA have been identified and tested in aquafeeds. Nevertheless, their prices are still too high to be commonly used in aquafeeds. Common carp (Cyprinus carpio) is one of the most cultured fish species in the world. In 2008, the world and the European production was 2 987 433 tons and 144 747 tons, respectively (FAO, 2011). It is an established cultured species. Carp is consumed as a traditional food in central Europe. Carp is an omnivorous species feeding on plankton and benthos as well as detritus in natural conditions. Typical farming practice in Central Europe is artificial shallow earthen ponds in which the production is based on plankton and benthos production supplemented by cereals or other additional feeds. The digestive system of carp is adapted to a diet including more carbohydrates compared to carnivorous species. The production cycle in Europe usually takes 3-4 years. There are two sources of n-3 HUFA in carp produced in ponds: i) the natural feed, plankton and benthos, being rich in n-3 HUFA and ii) the n-3 HUFA synthesized by carp from alpha linolenic acid (ALA). It has been reported that carps, in contrast to marine fish, are able to bio-convert ALA to n-3 HUFA (Zheng et al., 2004; Tocher, 2003). It is therefore of interest to understand and maximize the ability of carp to synthesize n-3 HUFA from ALA in order to preserve the lipid quality of the fish as human food and for sustainable utilization of feed resources. Carp culture might therefore be suitable of becoming net producer of n-3 HUFA by selecting fish with high enzyme activities in FA elongation and desaturation. Carp has also relatively low requirements for both n-3 and n-6 FA (0.5–1%) which can be fulfilled by plant 18 carbon FA (Takeuchi 1996 ). Inclusion of fish meal in carp culture is low (5%) (Tacon & Metian, 2008) and fish oil being even absent. Thus the substitution of these ingredients will be considerably easier for carp compared to carnivorous aquaculture species. Carp culture might therefore be an example of long term sustainable production without relying on the supply of fish oil and fish meal. In addition, carp culture turns “lost” nutrients (especially N and P) in water into a highly valuable nutritious flesh by the natural food chain in the ponds. The low trophic levels are especially important source of valuable n-3 HUFA in central parts of continents where the populations have less access to marine fish from capture. In addition, omega-3 carp has been produced by changes in additives into the pond feeds such as rape- and linseed cakes. By this strategy, a production of a stable omega - 3 lipid profile carp has been enabled. Studies on beneficial effects of fish intake are very often directed towards marine fish and shellfish. EPA and DHA are therefore misleadingly called “marine” fatty acids or “fish” fatty acids. These n-3 HUFA are to a large degree synthesized by microalgae, both in fresh- and saltwater and transported via the food chain in the systems. Collaboration with the Institute of experimental medicine IKEM, to investigate the effect of carp on cardio-vascular indices of subjects in SPA treatment has been started. Influence of carp (carp with increased content of omega 3 fatty acids) consumption on patients after cardiac revascularization surgery during the follow up SPA treatment was studied. Plasma lipids, LDL cholesterol and TG levels improved significantly in the group of patients receiving carp compared to the control group receiving chicken as the animal protein dietary portion.