Almost 97 per cent of global carp production today comes from farms. Genuine wild stocks are only to be found in a few waters, and the original wild carp is considered threatened. The carp that swim in natural waters are mostly farmed forms which have been released intentionally or have escaped from aquaculture facilities. Since carp can live for more than 50 years they can be found today in numerous waters. Carp particularly like slow-flowing or standing waters, such as the middle and lower reaches of rivers, but also ponds and lakes. There the fish like to keep to shallow vegetated coves, or shallows near the riverbanks. Although carp can survive cold winters they hardly eat or grow during such periods. They like warmer waters and the optimum water temperature for growth is above 20° C. This makes it clear why despite many centuries of selective breeding that has produced at least 30 to 35 breeds throughout Europe, the species can only exploit its full growth potential in the southern regions of the continent. Apart from temperature, however, the requirements for the water parameters are not high. Carp tolerate salinities of up to five per thousand, pH values between 6.5 and 9, and can survive low oxygen concentrations of 0.3 to 0.5 mg/litre.
Carp are often said to be herbivores, but in fact they are omnivores, for they make use of a wide range of food of both vegetable and animal origin. They eat insect larvae, worms, mollusks, and also occasionally young fishes, aquatic plants and other organic material, which is crushed with the fish’s strong pharyngeal teeth which are located on the rear gill arches. For this purpose, the pharyngeal teeth rub against the lenticular, curved, hard lapiscarpionis, a plate between the indentation of the occipital bone and the first vertebra. Carp finds its food preferably in the bottom water layers or in the muddy bed of ponds and rivers. They usually begin to search for food at dawn, using their two pairs of barbels on the upper lip for detection and then sucking the food in with the trunk-like protuberant (protractile) mouth. With good nutrition and optimum temperatures carp can grow by 2 to 4% of their body weight daily. In tropical and subtropical areas growth of 0.6 to 1.0 kg per year is possible. In the temperate regions of Europe, on the other hand, carp need two to four growth periods (summers) to reach weights of between 1 and 2 kg.
Selective breeding for many centuries
Carp were already cultivated in China more than 2,000 years ago, and the ancient Romans kept them in reservoirs (piscinae), from which the pond systems of Christian monasteries developed centuries later. The distribution and the fate of the species have always been closely linked to the cultural history of the human race. Carp was one of the first fishes that humans tried to domesticate. Initially the ponds were stocked with wild fish from natural waters but from the 12th century onwards the early pioneers of central European fish farming developed methods for producing the required fry themselves and carried out selective breeding to produce the desired results. By always using the biggest, most handsome specimens for reproduction, a genetic selection took place intuitively, which ultimately led to the well-known robust, long-living forms that produce a good share of meat. While the wild fish still had an elongated, completely scaly, shiny bronze body, the breeding forms were usually stocky, high-backed, and naked except for a few remaining scales. Their backs shimmer dark olive-green, their bellies are yellowish to whitish.
Four different breeding forms of carp can be distinguished on the basis of their scaliness:
• Scaly carp – all scales intact as in the original form, but the body is more compact.
• Mirror carp – the most frequent breeding form with irregularly distributed, different sized scales, mostly along the lateral line and at the fin base.
• Linear carp – a row of mirror scales of equal size runs along the length of the lateral line.
• Leather carp – body largely naked, only isolated scales at the fin base.
Historians are in the meantime quite in agreement that the natural advance of the carp into the upper reaches of the Danube, into Lake Constance and the river Neckar was promoted 8000 years ago by a brief period of warmth in the climate. It is unclear, however, why during the transitional phase from the early to the High Middle Ages more than 1,000 years ago this fish species got into Central and Western Europe. Sceptics do not think that the isolated cases of the species being kept in monasteries are on their own sufficient to explain the very widespread distribution of the fish in Europe. Especially since at that time it was only monks and nuns who, in an attempt to make their diet more varied during the fasting season, had the necessary expertise to keep and reproduce the fish – and they kept their valuable knowledge very much to themselves. It was during that period that some of the pond systems that still characterize a number of European regions today and are often still used for the cultivation of carp were developed. For instance, in Oberlausitz, where 335 ponds today constitute the largest commercially used pond area in Europe, or the Austrian pond areas in Waldviertel, Burgenland and southern Styria.
One of the most important aquaculture species worldwide
While carp are often grown in polyculture in Asia, monocultures are clearly preferred in Europe where the carp are reared in shallow ponds with plenty of nutrients. The ponds’ dams are usually densely covered with reeds and water plants. Additional feeding with grain or feed pellets is common in order to maximize growth potential during the warm season. The beginnings of this traditional, controlled and near-natural farming method date back centuries to a time when river courses were dammed to power water mills. The water retention basins ("mills ponds") were often also used for rearing carp. Today, the spectrum of carp farming methods ranges from extensive natural ponds, the net pens known from aquaculture, and flow-through systems with channels or round basins, to intensive recirculating systems (RAS). About 4.2 million tonnes of carp were produced worldwide in 2014, mainly in Asia, which accounts for almost 95% of global carp production. Cyprinus carpio thus ranked fourth in volume terms among the most important aquaculture fish after the grass carp (Ctenopharyngodon idellus) with 5.5 million tonnes, the tilapia species with 5.3 million tonnes and bighead carp (Hypophthalmichthys nobilis) with just under 5 million tonnes. At least in Europe, however, the importance of carp farming goes far beyond the mere production of food fish, because carp ponds are also of great ecological importance since they serve as a habitat and retreat for many endangered animal and plant species.
On the surface, global carp landings from fishing don’t seem particularly important with only 145,566 tonnes. This impression is deceptive, however, because to the catches of commercial fishermen must be added the quantities caught by many hundreds of thousands of sports fishermen, and they are not included in the FAO statistics. Carp is popular with anglers because they grow very big, are strong fighters and can be baited selectively with suitable lures (boilies). Many anglers prefer scaly carp to the domesticated breeding forms because they put up more of a fight on the hook. A significant proportion of aquaculture production in Europe is used to stock natural waters with carp. Often, it takes years for the fishes to be caught. And this is quite visible in the fishing records reported by proud anglers. The current world record for mirror carp was registered in Hungary in 2012, where a fish weighing 46.1 kg with a length of 113 cm was landed. In the case of scaly carp, the record is 45.5 kg. (This fish was caught in the French Etang de Saussaie in 2013.) Some anglers let the fish go again after the catch. This practice meets with violent criticism however, especially with animal protectionists who argue that “Catch & Release” contradicts the Protection of Animals Act which prohibits the inflicting of suffering on a vertebrate without reasonable cause.
Targeted control of carp as an invasive species
Carp is not welcome everywhere, however. In Australia the farming and release of the fish is even prohibited by law because it is considered an invasive species which, through its digging activity in the sediment, clouds the water, damages the ground vegetation and frees bound nutrients. Immigrants had introduced the carp to Australia in the 19th century. Then in the 1960s their number exploded after animals had escaped into the wild from a fish farm. In the Murray-Darling Basin, for example, carp accounts for over 80% of the total fish biomass and the situation in many other waters is no less severe. That is why the fish is considered a pest and attempts are being made to eradicate it… For example, by releasing genetically modified carp into the waters in the hope that these will then cross into overgrown populations and lead to pure male offspring. So far, however, these efforts have had only limited success. In 2018, the Australian government plans to launch a new project and introduce herpes viruses in a river system in southern Australia. The viruses supposedly kill only carp, while the native species are spared. The government is planning to spend 10 million euros on the programme, which is to kill 95% of the ever-expanding carp population within 30 years. But this herpes virus plan, also called "Carpageddon" by critics, is controversial. What, for example, is to be done with the fish carcasses, should it really come to a mass death of the carp? Apart from that, the use of viruses involves considerable risks because they mutate quickly and unpredictably and may have completely different effects than originally intended.
Just how difficult it is to control and fight viral diseases can be seen in the example of the Koi Herpes Virus (KHV), which is actually called Carp Nephritis and Gill Necrosis Virus (CNGNV). Since the beginning of the millennium, it has caused economic damage in European carp farms and has even penetrated natural waters. The increasing intensity of carp production in some areas and the interregional transport of fish make it difficult to combat this disease. A further complication is that many traditional medicines (fungicides, antibiotics and insecticides) are not authorized in the EU, so that there are hardly any therapeutic options available. At present high hopes are placed on immunostimulants to increase the natural resistance of the fish. However, research in this field is still at an early stage and it will probably be years before appropriate vaccines are available. Just as important is the development of reliable diagnostic tools to detect bacterial and viral infections in the pond farms with the desirable speed and certainty. With the EU Directive 91/67 / EC which has been amended several times over the years and is now available in the version of 29 November 2008 and lays down the animal health conditions for placing on the market of aquaculture animals and products the Community is trying to improve protection against fish diseases. However, there are doubts as to whether the legislation will be able to cope with the epidemic risks of European aquaculture that is even partially networked worldwide. Plagues like KHV cannot be controlled or restricted by countries acting alone. Fish diseases spread across national borders faster than legislature is able to follow with new regulations. Europe needs a reporting and monitoring system that will enable all industry participants to react quickly to epidemic outbreaks.
Inconsistent product quality leads to marketing problems
Although the importance of carp for European aquaculture and fisheries has decreased, the fish continues to play an important role, especially in Eastern Europe. In many places, carp are regarded as a festive must, especially at Christmas and New Year. In Poland and the Czech Republic these public holidays are hardly conceivable without carp. On the menus of Czech restaurants at that time you can often find five to ten different dishes, from carp boiled in a spicy stock, and grilled carp, to quite hot varieties with paprika. In Germany the region of Franconia is considered a primary centre for carp. There, the fish (head-on, fins intact) is split into two halves along its length, rolled in flour and baked in fat (“Karpfen fränkisch”). In Northern Germany the carp is often marinated in a vinegar-wine sauce for 10-15 minutes. The acid in the vinegar causes the fish to lose its sliminess but it also turns the fish a blueish colour, which is why this recipe is called "Karpfen blau”.
According to FAO statistics the largest common carp producers in Europe (as of 2015) are Russia (57,983 tonnes.), the Czech Republic (17,860 t.), Poland (17,749 t.), Hungary (10,725 t.), Ukraine (9,640 t.), Belorussia (6,480 t.) Serbia (5,598 t.) and Germany (4,916 t.). To fill the gap between supply and demand around 24,000 t. of carp and carp products (live, fresh-chilled, frozen) are traded every year throughout Europe. Important exporters are Austria, the Czech Republic, Croatia and Lithuania, and the importing countries are mainly Germany, Hungary and Poland. Intra-European trade with carp accounts for roughly two-thirds of world trade with this fish, because in the main producing region – Asia – carp is hardly traded internationally.
However, in some European countries and particularly among young people carp has an image problem and is to be found rather low down on the list of consumer favourites. This is due not only to the annoying bones that are a problem for many people when eating fish, but also to the strongly fluctuating taste and varying quality of the fish. The flavour and consistency of carp depend very much on the feed used (grain, corn, soy, pellet feed), the farming conditions and water quality. If the carp is too lean, it often tastes like straw and bland, but if it is too fat, it can develop a rather musty aroma, something which can be attenuated, however, by keeping the fish for a long time in clean water. What is lacking are attractive carp products which could promote sales outside of the typical marketing season. Admittedly, there have always been promising approaches and new product ideas but none of them have been successful. The future fate of the carp in European countries probably also depends on whether more fish-eaters – especially young people – can be attracted to this fish.