Consumption behaviour in western countries is rather odd: fish species that are easy to reproduce and farm, for example a lot of cyprinid species, attract only little interest whereas demand is high for species whose farming is very difficult and only partially understood, or is not even possible yet at all. One only has to think of eel or bluefin tuna which enjoy consistent popularity: demand for these species is in the meantime higher than supply. Both of them are produced in aquaculture but the necessary fry – glass eels and young tuna – are still taken from natural stocks. The two species are thus farmed in capture based aquaculture which does not take the pressure off wild stocks but even weakens them. Scientists all over the world are working intensively to discover the secrets behind reproduction of such difficult species with the aim of meeting fish farms’ fry requirements through artificial reproduction and enabling better understanding and control of the technology required for reproduction. Although notable progress has been made in the reproduction of several tuna species in recent years it still doesn’t look as if a solution will be found in the near future.
The bluefin species from the Atlantic and the Pacific are of course particularly attractive for aquaculture. They account for only 0.9% of tuna catches from fisheries but they are very valuable, and demand for them is high, especially on the sushi and sashimi markets. It is thus hardly surprising that nearly all tuna farms have specialised in these species. The young tuna required for farming – mostly fishes weighing 15 to 45 kilograms – are caught very carefully in the sea and put into huge floating net cages measuring 100 m and over. The preferred fishing gear is the purse seine, or occasionally traps or rod and line with smooth hooks. In order to reduce stress the tuna are often taken directly within the fishing gear to the net cages – sometimes over distances of several hundred sea miles. The speed at which this is carried out should not be too high because otherwise the lactic acid concentration in the fishes’ muscles increases too strongly and with it the fishes’ mortality. Younger tuna seem to be more resistant to stress than older ones.
On average, the tuna remain in the net cages for three to six months. During this time they are fed on low-priced fish species such as herring, sardines, anchovies, sardinella or mackerel which increases their weight considerably. They are usually only harvested to order when the quality and size – and the price – of the fishes is right. Several methods are used for removing the fishes from the net cages. In Australia and Croatia the net is narrowed down until the individual fishes can be caught by hand. Undamaged fishes have the highest quality (“toro”). After killing and bleeding they are quickly cooled so as to avoid histamine development. The destruction of the spinal cord with a wire prevents spasms within the muscles when the fish dies which would lead to development of lactate and reduce the quality of the fish. If lactate concentration is too high the fish are termed “yake” (Japanese for “burnt”) and this makes them unsuitable for sashimi. In Malta and Spain the tuna are driven into a funnel shaped fishing net that is hung into the net cage. Electro harpoons are also used for harvesting.
Technology for “real” tuna farming is still evolving
The first stages of this farming technology date back to the year 1985. In the meantime there are farms on most of the world’s continents. In the Mediterranean tuna are farmed all around Sicily and Malta, off Spain, Croatia, France, Tunisia and Algeria. Production fluctuates strongly from year to year and can only be roughly estimated. Ten years ago 11,000 t are said to have been produced in the Mediterranean region alone. At that time this quantity was equal to about half of global production of tuna in aquaculture. In 2005 the FAO named worldwide production at 22,995 t. The aquaculture industry’s figure for the same year is higher, however: 32,500 t. In 2010 FAO statistics stated a total volume of 9,412 t, of which just under half, or 4,000 t, were Atlantic bluefin tuna (Thunnus thynnus), 3,324 t were Southern Bluefin (Th. Maccoyii), and 2,000 t were Pacific bluefin (Th. orientalis).
Japan is the main buyer of tuna from aquaculture. Although farmed tuna account for only 4% of the Japanese tuna market they are of huge significance because they are practically all (100%) traded in the high-value toro segment (the toro share of tuna from the fishing sector is about 30%). Japan’s sashimi market is in the meantime largely saturated, however. The further development of tuna farming will thus depend on the development of new sales markets. There are hopes that this will be possible in the USA which buys at least 45,000 t of premium-quality tuna (sushi, sashimi, barbecue) every year.
Solving some of the problems that currently still restrict production increases will be decisive for the future development of tuna aquaculture. A particularly urgent need is for regular hatching of the fishes since that is the only way to meet the farms’ demand for fry without further weakening wild stocks. Equally important is the development of a viable dry feed that corresponds fully to the nutritional requirements of the tuna. Although progress has been made in both these areas in recent times we are still a long way from a breakthrough.
Researchers at Kinki University in Japan (where the first farming experiments took place in 1979) have been particularly successful with hatching bluefins. In 1989 the fishes spawned for the first time in the cages and in 2002 the researchers succeeded in closing the reproduction cycle completely, when tuna that had been raised in aquaculture spawned and supplied eggs themselves for the first time. Because hatching tuna demands tremendous know-how and is very expensive it is still not possible to get by without using wild fry, however. Yellowfin tuna are produced artificially on a relatively regular basis, too. In tanks at the Achotines Laboratory of the Inter-American Tropical Tuna Commission (Panama) yellowfins have spawned nearly every year since 1996. The larvae and young tuna are still being used for scientific experiments and farming experiments, however. The Stehr Group in Australia also attracted attention recently with their successes in farming Southern bluefin tuna.
The development of a dry feed that is suitable for tuna would make farming easier and more effective. Because wild fry are conditioned to eating fresh feed in the net cages, making it hardly possible to switch their nutrition to dry feed, they are currently mainly fed on trash fish or bait. This feed is often supplied frozen which leads to considerable expenses for storage, transport and feeding. Apart from that, the feed conversion ratio (FCR) is very high with values between 10 and 15. In other words it takes 10 to 15 kg of fresh fish to produce one kilogram of tuna. In the meantime the first commercial pellet feed products are available on the market (for example Cargill / USA offers a complete tuna feed containing 45% protein and 20% fats that are protected against oxidation by a special technique) but these products have still not been able to assert themselves in practice in capture-based aquaculture.
Cobia and yellowtails still too expensive for the mass market
Whilst tuna farming is still in its infancy the production of other high-value species such as cobia (Rachycentron canadum) or yellowtails (Seriola spp.) has become almost routine. The firm white flesh of the cobia which is also traded under the names black salmon, runner, black kingfish, crabeater, cubby yew, prodigal son or sergeant fish is similar to that of blue merlin and is not only in Asia in high demand for sushi and sashimi. The fish grows very quickly and can grow from a 5-gram fingerling to a sales weight of 5 kg within just a year. Optimistic aquaculture experts predicted for cobia similar success as for salmon but this has so far not come about. For the vast majority of consumers the fish is simply too expensive: its sales price is around 15 USD/kg. So although the number of farms is increasing worldwide production is only growing slowly. According to FAO statistics a good 40,000 t were farmed in 2010, particularly in Taiwan and China which contributed more than 90% to total production. The relatively high price of the fish results from its feed requirements, for cobia is a predator that mainly eats fish, and accordingly needs protein-rich feed. Apart from that, raising the fry is not easy, and farming technology still has room for development. The larvae initially have to be fed on zooplankton and later this is switched to dry feed. If the feed isn’t exactly right, the young fishes start eating one another. If it proves possible to stabilize the early stage of farming and further reduce production costs cobia stands a good chance of future success. After all, with an FCR of about 1 this fish reaches a marketable size of 5 to 7 kg in just one year. Salmon takes three times as long.
Yellowtails (Seriola spp.) are to be found in the same league as cobia. All Seriola species stand out for their white, tender, tasty meat. Because yellowtails from aquaculture have a high fat content their meat is popular in Japan where fat is considered a particular quality feature, and farmed yellowtails are therefore even more appreciated than their wild counterparts which are often leaner. The market prices for farmed yellowtails are thus about twice as high as for wild catches. In 2010 nearly 160,000 t of yellowtails were produced worldwide in aquaculture. Japan contributed 139,000 t to this total. Japanese farms mainly produce Seriola quinqueradiata. Although it is already possible to hatch this species artificially most of the fry still come from wild catches (capture based aquaculture). This is likely to change soon because Japan now restricts the removal of wild juveniles in order to protect wild stocks. In recent years, however, even the permitted volume of about 40 million juveniles (30-100 g) was rarely fully used. The catch figures were often only 25 to 30 million fishes.
In the meantime other countries have recognized the market potential of the Seriola species and now two further representatives of this genus are being produced in aquaculture: yellow-tail kingfish (S. lalandi) and amberjack (S. dumerili), for example in Taiwan, New Zealand, Australia, Ecuador und Vietnam. Spain had begun testing production, and Italy, Croatia, Greece, Malta and France have also tested farming possibilities.
The fish are mainly produced in floating net cages. A light current, clean water and constantly high temperatures (the fishes stop eating at temperatures below 15°C) are essential for good growth. If fed well the fishes grow quickly. Fry weighing 50 g can reach weights of 200 to 700 g in a few months and up to 2 kg are possible after seven months. The fishes are mainly fed on fish. The FCR is somewhere between 5 and 7. If accordingly conditioned, fishes also eat dry feed, however.
Dashed expectations among many caviar producers
Some fish species that are still largely unknown in western countries have been farmed for a long time in Asia. One such is snakeheads (Channa spp.). The low-fat, white meat of these fishes and the fact that the fillets are almost boneless would presumably give them good market chances in Europe. The Channidae family (snakeheads) comprises 12 species that are to be found almost throughout the whole of South East Asia. All Channa species are air-breathers and so they can be farmed in swamps, water channels, rice fields, oxidation ponds and other waters with low oxygen concentrations without problems. Production volume of these fishes increased more than thirty-fold within a decade. However, there are only a few companies that have specialised in Channa farming, which requires a lot of experience because snakeheads immediately become cannibalistic if the feed quantity and quality is not right. In the farms they are usually fed on fish waste and innards from poultry slaughter. Instead of being produced in specialised farms Channa are thus sooner produced as a side-line in rice fields and other water reservoirs. Production volume is likely to grow further if it is possible to solve the bottleneck in fry supply. Channa take care of their young: males and females build the nest and watch over their young together. They mostly spawn at the beginning of the monsoon rains. It is possible to stimulate maturity using hormones but this is hardly done in practice at present.
A number of sturgeon species (Acipenseridae family) have been counted among the promising candidates for aquaculture during the last two decades. The collapse of the fishery for wild sturgeon and the possible profits from caviar awakened in investors and unfortunately in some speculators hopes that the difficult, expensive farming of these fishes could prove worthwhile and produce attractive profits. Since 1997 trade with sturgeon and sturgeon products has been regulated by the Washington Convention on International Trade in Endangered Species. 23 sturgeon species were listed on the CITES annex list II, two species are even on list I. Since then it has been necessary to have special approval to trade sturgeon and sturgeon products on the world market (“CITES permission”). According to FAO statistics 328 t sturgeon were produced in aquaculture worldwide in 1990. This figure had risen to just under 20,000 t in 2005 and production today probably amounts to much more than 40,000 t. China is by far the biggest producer. Whether sturgeon production will continue to increase at the same rate in the future seems questionable since the expected profits from caviar often remained behind expectations. There are numerous different reasons for this: quality problems, too much caviar on the markets, and low demand, presumably partly due to the financial and economic problems in some European countries. It seems that consumers in these countries can soonest do without caviar in such difficult times.
Demand for special aquaculture products is often only regional
Promising candidates for aquaculture are not only to be found among fishes but also in other animal groups, for example echinoderms which are very popular in individual markets and promise high profits. Sea urchin roe, for example, is one of the most expensive seafood delicacies in the world. In Japan some sea urchin species and sizes are traded for 6 to 7 USD per piece, their roe costs 340 USD/kg and more. Because the wild stocks of these sea urchin species are often overexploited, aquaculture offers an attractive alternative. However, farming these creatures in aquaculture is not easy and hardly any of the attempts to date have been really successful. People have tried to produce sea urchins in polyculture together with fishes, for example: the sea urchins were to feed on the algal growth that developed on the nets. In practice, however, this feed often proved insufficient, particularly since the algae were covered over with fish faeces. On top of that it was no longer possible to clean the nets by hand due to the risk of injuries caused by the sea urchins. Despite such difficulties interest in sea urchin farming remains high, however.
In Norway an automated system has been developed for sea urchin farming. It consists of a floating raft from which lattice-work boxes are hung into the water like the rungs of a rope ladder. The boxes are hauled to the surface for feeding and controls. Due to the high level of this system’s automation only two operators are needed to manage a farming facility measuring 3,000 square metres. At least six sea urchin species are farmed in China, mostly Strongylocentrotus intermedius, which was introduced from Japan in 1989 and is the most commercially important species. It is mainly produced in the coastal provinces Liaoning and Shandong. During farming, use is made of submerged cages which hang down into the water from rafts. Young sea urchins measuring 1 to 1.5 cm in diameter can grow to a marketable size of about 5 cm after 12 to 18 months. They are mainly fed on kelp algae. In some countries sea cucumbers (Holothuria) are also very popular, particularly in Asia, where, in addition to shark fins, abalone and swim bladders of fishes, they are one of the “four treasures of the sea”. Today a lot of wild stocks are overexploited or exhausted, some species are under CITES protection. The price for live organisms of the sea cucumber species Apostichopus japonicus, the most important of the 20 species that are eaten in China, rose four-fold in recent years to 25 USD/kg. Due to strong demand they have been farmed in China for decades, but aquaculture did not begin on a large scale until the mid-1990s. Sea cucumber production also has to cope with supply problems of stocking material. In just under two weeks the cucumbers go through eight development stages from the blastula to the juvenile sea cucumber and have to be fed on three microalgae for their first feed. The feed density has to remain at a consistently high level and the temperature must not deviate more than 3°C from the optimum. Sea cucumbers are sediment eaters and as such they reduce organic contamination on pond beds and below aquaculture facilities. For this reason they are also produced in polyculture with shrimps or suitable fish species.