H.C.M. van Herwaarden
Alongside most other species of aquatic animals produced for human consumption, the aquaculture production of Anguillid eels has shown a staggering growth in the last few decades. Global eel production in 2001 was estimated by FAO at 231,000 MT and is predominantly concentrated in the Far East (China 155.800 MT, Taiwan 34.000 MT, Japan 23,100, Malaysia 2,400 MT, and Korea 2,600 MT) and a few countries in Europe (10,200 MT). In Europe the only species cultured is European eel (Anguilla anguilla), whereas in Asia the Japanese eel (A. japonica) is the main species cultured. However, due to shortages of seed fish of the Japanese eel in its native range a considerable amount (50,000 MT) of European eel is produced in this area as well.
Although eels can be found on the menu in many countries, the major market for Eel is limited to Japan and a small number of European countries including Italy, Germany and The Netherlands were they are considered a delicacy. The market value of eels depends on the species and varies between different countries. Currently prices range from 3-15 US$/kg which rank the eel among the most precious species of food fish.
In the Philippines eels are, despite their rarity, widely accepted as a food fish and are considered by the Chinese community as a delicacy reserved for special occasions because of its delicious sweet meat. Because of this local eels fetch prices as high as PHP 500/kg. So far, almost the total domestic production of eels (±200 MT) in the Philippines originates from capture fisheries. Besides a few undeveloped backyard operations, no significant industrial production of eels does occur in the Philippines. Considering the high prices for eel on both the domestic as well as the export market, the fact that environmental conditions are close to ideal and seed fish are readily available, there exists a huge potential for a viable industry to develop. The aquaculture production of eel is a paying business with short term high revenues and a short start-up period of less than two years.
Biology of eel
Riverine eels have a complicated and intriguing live cycle which is still not completely understood. Eels live in freshwater but migrate to the ocean to breed. Every year adult eels migrate from their freshwater habitat to the spawning grounds in the ocean where it is thought that they spawn at depths of around 100-400 m. It is believed that eels spawn only once in their lifetime, after spawning it is presumed that the adult eels die.Eggs hatch and develop into a pelagic leaf-like larvae called ‘leptocephali’ which are carried away by the ocean currents. After a voyage of one to two years they metamorphose into tiny transparent ‘glass eels’ and reach the continental shelf where they are attracted by riverine estuaries. In schools they actively migrate from the salt to fresh water. During this phase they further develop into the pigmented elvers which already resemble the adult stage. Newly pigmented elvers have a total body length of about 5-7 cm.
Adult eels have a round, elongated body and generally become 50 to 100 cm long, but can grow in some species up to a weight of 3-3,5 kg at an age of 10 years. The males, however, remain small and do not grow beyond 300 grams. The skin colour of the eel varies, depending on the age of the eel, the environment, and the physiological stage. Young eels are generally lighter in colour with a yellowish belly (‘yellow’ eels) while adult eels, in the migratory period, are darker with a silvery-coloured belly (‘silver’ eels).
In their natural habitat eels are top predators that feed during the night on small fish, amphibians, crustaceans, echinoderms, insect larvae, etc. Once attaining maturity at an age of 5-15 year, the female eels stop eating, change body shape and colour, develop the reproductive organs and migrate to the sea. Males become mature before the females.
Pollution of the environment, over fishing of market-sized fish and in particular of glass eels have resulted in a decline of the natural stocks of the European and the Japanese eels in their native range.
The Philippine archipelago accommodates four of the total 16 species of eel found around the world. The most widespread species is A. marmorata which can be found throughout the archipelago. Anguilla bicolor pacifica inhabits the Southern part of Luzon, the Visayas and Mindanao whereas A. celebensis can be found in western half of the archipelago. The three above mentioned species are known as tropical eels. The Japanese eel (A. japonica) is an species from the temperate regions that also appears to occurs in the Northern part of Luzon.
Unlike for most other commercially cultured fish species it is not jet possible to produce eel seeds. Although several institutions in the world claim to have successfully hatched artificially produced eggs, nobody has been able to rear the larvae up to a size that can be used for grow-out. As a result eel farmers fully depend of fish seeds (elvers) from the wild.
Two systems to grow eels are currently known; the stagnant pond system which is widely adopted in Asia and the super-intensive recirculation system which recently independently evolved in Northern Europe.
Stagnant pond system
The first records on eel culture are from Japan and go back as far as the late nineteenth century. Traditionally eels are produced in stagnant ponds in a similar fashion as was the case for most fish species for a long time. Ponds that are used for eel culture have an earthen bottom but have lined pond banks to avoid escape of the valuable stocks. The water required for filling the pond and for water exchange is usually pumped up from a shallow bore hole but occasionally is also taken from rivers. Propagation of phytoplankton is applied to provide the eels with appropriate levels of oxygen and natural shade. Natural decomposing processes in the water body and the pond bottom take care of the breakdown of wasted feed and excreta. If needed, oxygen is added to the ponds by means of surface aerators such as paddle wheels.
As eels have a strong tendency to cannibalise they have to be sorted and graded often. As a result a single stagnant pond farm needs a large number of ponds to accommodate the different grading fractions. These ponds are named after the stage of the fish, i.e. older elver, fingerling and adult ponds which have an surface area of 40-100 m2, 80-300 m2 and 200-1,000 m2, respectively. Elvers on the other hand are weaned and reared to the older elver stage in flow through tanks. The stocking density applied varies from 0.4 to 4 kg/m2 depending on size of the fish and the size of the ponds. Fish can be feed with raw fish (FCR 7) but at precense many farmers make use of artificial feeds in the form of pastes of pellets (FCR 1.4). The length of the production cycle depends on many factors but normally lies between 1.5-2 years.
The open pond system which were used for intensive aquaculture have been superseded in the last thirty years in Japan by ponds in temperature controlled green houses, in which eels can be raised to marketable size in half of the time taken in open ponds.
Super-intensive recirculation systems
Decreasing catches from natural stocks and the high market value of eels created a strong interest in the culture of this fish in non-traditionally eel producing countries in Northern-Europe in the last two decades. The unsuitable environment for eel culture in ponds, high prices of land and usage of water, stimulated the development of modern technologies in husbandry, water management and nutrition that enabled high stocking densities in this area. This accumulation of knowledge has resulted in efficient high yielding super-intensive recirculation systems in which the fish environment is optimised and fully controlled by the farmer. This development predominantly took place in The Netherlands and Denmark, which experienced an impressive growth and currently produce an estimated 4,000 and 2,100 MT of eels, respectively.
The super-intensive eel culture is carried out indoors under dimmed light conditions in tanks of 5-30 m3 with a high level of water exchange. In water recirculation systems, instead of being released, the waste water is recycled after mechanical and biological filtration and injection of pure oxygen. A combination of good water quality, appropriate temperature and oxygenation can allow stocking densities of over 150 kg/m3 without compromising the health or welfare of the fish.
Feeding is almost exclusively done with pelleted feeds. These extruded commercial feeds can be applied from elver stage (0.3 g) up to adults up to a weight of 1 kg and are usually supplied in the form of granular crumbles or pellets. The specific growth rates (SGR) and feed conversion ratio (FCR) that can be attained with these feeds vary with type of product and fish size. The SGR for glass eels varies between 3-3.5 %, though occasionally may be as high as 5 %. The average FCR for glass eels generally lies below 1.0. For ongrowing eels the SGR ranges from 0.5-2.0 %, while the FCR's range from 1.2-1.4, although sometimes these can be as low as 1.1. Although, recommended feeding tables exist, most farmers will opt to feed to satiation to guarantee highest growth rates. This optimizes the production in kilograms per square meter and reduces cost price. At a culture temperature of 25 oC this normally will result in feeding levels for glass eel and elvers between 2–5 %/day, and for ongrowing between 0.8-2.5 %/day.
Despite the high operation costs for these systems (balanced artificial feeds, power, pure oxygen, labour) and high initial investment these operations have shown to be economically viable because of the high level of efficiency.
Eel culture prospects for the Philippines
Most species of eel require culture temperatures in the range of 25-30 oC and a reliable source of fresh water from a bore hole. In the Philippines these two preconditions can be easily met throughout the year. In areas where water temperatures go outside the optimum range these can be corrected by use of simple green house technology.
Seed fish of the most valued species of eel (A. japonica) is readily available at low prices in Northern Luzon. Unfortunately, the populations of glass eels that enter the rivers in this part of the country are a mixture of 2-3 species and include tropical species of lesser commercial interest for the export market. Because of this it may be necessary to rear the seeds to a certain size before these can be sorted for grow-out. The cost of the mixed glass eels and the operational expenses to rear these fish to this stage will only be limited and it is not expected to become a bottle neck for the success of an operation. Moreover, the value for tropical eels on the domestic marked is very respectable as mentioned in the introduction. For this reason also these eels can be considered for grow-out.
The Philippines has a vast and long tradition in aquaculture. As a result skilled labour on both management and utility level can be found. However, the aquaculture sector has little experience with complex super-intensive productions systems. In this respect there is a gap that needs to be bridged. On the job training and appropriate system design should make it possible to fill this gap.
High quality feeds for eels are presently not available in the Philippines but can be produced locally as several renowned fish feed processors are operating in the Philippines. Once a demand for eel feeds occurs it is expected that these companies certainly will want to suffice this. Alternatively, feeds could be imported from either Japan, Taiwan or Europe.
A major bottleneck to the success of a potential project may the frequent occurrence of violent typhoons and frequent electricity burn outs. The effects of these however, can be limited by sensible farm design and inclusion of a standby generator.
More than 230,000 MT/yr of eels is produced worldwide, with the main producers being China, Japan and Taiwan. Over 40% of this production is produced for the Japanese ‘Kabayaki’ market. Kabayaki is a style of serving eels, where eels of around 150-200g are butterflied, placed on skewers, basted in a thick soy based sauce, and steamed or grilled. More than 90% of eels consumed in Japan are served this way, with eel being the most widely consumed freshwater fish in Japan.
Declining eel stocks overseas may work to the advantage of Philippine producers. The Philippines are fortunate not to have problems experienced by other countries, such as waterway pollution, disease and particularly excessive over-harvesting of glass eels. Already at this time China, Japan and Taiwan import glass eels from Europe, Australia and the Philippines to supplement the domestic requirement of eels seeds. As natural stocks in Europe are declining there is a strong call from environmentalists and farmers to limit the export of glass eel. Even more as transit losses are unacceptably high. Taking this into account it can be anticipated that the supply of eel will decrease in the coming time. Instead of exporting glass eels from the Philippines, value could be added to this commodity by growing them locally. It can be foreseen that there will be great potential for Philippine producers to step in and replace some of the shortfall in supply that may arise overseas. The Philippines have a good advantage over other countries as it has good shipping facilities and is closely located to the main eel consuming countries.
In conclusion, the low cost of land and water, skilled labour in the Philippines, combined with the favourable climatic conditions and reasonably good infrastructure allow for the development of a healthy long term eel culture in the Philippines.
Eel project options
Eels are known to hide in crevices and in the mud but also have the ability to get out of the water and move away in search of new territory during damp weather. This is especially true for the elvers and juvenile stages. It is this behaviour that enables eels to settle in the most unexpected locations. This characteristic has strong implications for the design of the holding facilities. Ponds need to have steep lined walls with a boarding of at least 25 cm and a overhanging rim to avoid escapes.
For long it has been demonstrated that eels can be successfully grown in stagnant pond systems. The production levels in these systems are however restricted due to the limited and unpredictable oxygen production capacity of phytoplankton, and the low natural removal rates for excreta and ammonia among others. As production levels in stagnant pond are relatively low (< 4 kg/m2) and many separate ponds are needed for the different size classes, the initial investment is for such operation is considerable. The operational costs on the other hand are low.
Alternative production systems aim at intensification of production per unit area by manipulating the fish environment. Basically there are two options; 1. to use a flow through system or 2. to use in-farm water treatment.
In flow through systems waste products are flushed out of the farm to be treated naturally elsewhere. For species such as eels that can be kept at high stocking densities oxygen is normally the first limiting factor in such a system. The flow of water through the system is determined by the biomass and feed consumption of the population. Typically, a standing stock of 10.000 kg would require a flow of 2000 m3/hour of well aerated water. In this case it is possible to have stocking densities as high as 100 kg/m3, which in super-intensive culture are not uncommon. In general, flow through systems are cost effective and simple to operate. Unfortunately, reliable sources of water (disease free) in high volumes are difficult to find while it is not feasible to pump these volumes of water up from a bore hole.
The flow of water in a system can be reduced by addition of aerators which can provide a substantial part of the oxygen requirement. This however will increase the operational expenses. The water exchange in this case is determined by the production of ammonia which is toxic to fish. The flow in this case would be reduced to 15-20 m3 per hour for the same standing stock.
The exchange of water can be further reduced by re-using (recirculating) the same water by using mechanical filters to screen off excreta, waste feed and suspended solids and bio filters to remove ammonia. The latter component is removed by converting it into the less toxic chemical nitrate. This process (nitrification) is carried out by aerobic bacteria that are attached to the surface of filter media. Applying bio-filtration is often applied in combination with injection of pure oxygen which enables even higher stocking densities. In this case the water exchange rate will be based on nitrite levels and will go down to only 1-2 m3 per hour. It may be obvious that production systems like this go hand in hand with high investment and operational costs and result in a high production costs per kg of fish. On the other hand it enables optimal control over fish stocks which can be cultured under the most ideal conditions, such as for example water quality, temperature and light regime. Culture of fish in tanks enables easy handling during sorting and grading of the fish which can greatly affect the growth performance of the fish. Furthermore, it is labour extensive. Intensification at this level is only possible for species of fish that have a high market value and can be cultured at high densities. For the culture of eel intensification is very well possible and certainly has good advantages over pond culture as mentioned above.
As the environmental conditions in the Philippines are favourable it is technically possible to apply the whole spectrum of possibilities for intensification of eel culture. Clearly, the choice of the level of intensification that can be applied strongly depends on the availability of a reliable source of water, the need to do so, and the economic feasibility. Taking these aspects into account a system with a moderate level of intensification that optionally can be combined with simple low cost filter systems, has been designed for the Philippines.
Eel project description
The specific design of a farm always strongly depends on local conditions. To give an impression a model farm for the production of 37,5 metric tons of eel with an harvest weight of approximately 200 grams is described roughly here.
The project includes three culture units; a glass eel/elver unit, a juvenile unit a the grow-out unit. The glass eel unit is used to grow wild caught glass eels and elvers to a weight of approximately 5 grams after which they are transferred to the juvenile unit. In the juvenile unit the eels are reared to a size of 50 grams. The fattening of the fish from a body size of 50 grams to market weight is finally carried out in the grow-out unit.
Each culture unit consists of a series of raceways that accommodate the fish. Culture water is re-used after it is thoroughly aerated. If necessary, these units are connected to a filter system that takes care for the removal of excreta, suspended solids and ammonia. In order to provide dimmed light conditions each unit is housed under a green house structure with shade covers.
Besides the systems there are shared facilities that include: an office, a workshop area, a generator/electrical room, and a food store. The farm requires an area of approximately 2000 m2, of which 1400 m2 is covered by greenhouses.
To run the farm a good manager is needed, as well as 6 labourers, including 4 skilled workers. The annual food consumption of the farm is about 50 metric tons and energy uptake is in the order of 95,000 kWh. Every year about 100 kg of glass eels must be purchased.
Eel project feasibility
An eel farm will only give revenues after about 1-1,5 years of operation. High quality management and farm equipment are needed to minimize the culture risks and maximize output. These are available but at a cost. Thus, a farm must have a minimum production size to reduce the fixed cost part of the production cost. In the example given below the annual production is targeted at 37,5 metric tons.
The main operational cost in the eel farm are food, power, labour and glass eels. Annual operational cost plus the fixed costs can be estimated at 5 million pesos. Whereas the investment to build the farm can be estimated at 6 million pesos, although with use of locally available inputs this cost can be reduced.
Once the production has stabilized at its optimum, after roughly 2 years of operation, the annual revenues can be estimated at 11-12 million pesos. Thus, the first 1.5 production years will pay back all the initial investment.
After year 2 the annual cost is about 5 million pesos with revenues in excess of 11-12 million pesos. The profitability of the farm after income tax ranges around 85%. In conclusion, growing eels requires a high initial investment and high operational costs but also gives a high return on investment. Provided the culture of eels in the tropics is developed in a appropriate way it is a lucrative business. AquaCrops has the technical knowledge and practical experience and would be pleased to assist you developing this interesting aqua-industry.
For more information contact the address listed below.