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Report 5 (of 6): Industr-eel
Revolution - Sweden
Introduction
While world eel production has been
declining due to overexploitation, the demand for
eels has been growing, leading to increasing interest
in intensive eel cultivation. Artificial reproduction
of eels has so far eluded scientists, but that hasn't
stopped eel farmers. Instead, young eels or elvers
are bought to eel farms to be raised to market size
so they can be sold. This system requires high-tech
filtering equipment to keep the water clean and does
not discharge effluent into the environment. The sludge
collected in the filtration system is used as fertiliser.
Helsingborg, in southern Sweden is
an unlikely place to find an active fishing industry.
It's a landlocked industrial town and the biggest
employer is a chemical plant. It's also home to the
Scandinavian Silver Eel farm, which is using some
of the latest developments in fish farming. The eels
produced have a good market in Scandinavia, Germany
and Holland and the farm processes them on site to
make fillets and smoked eel, as well as selling them
to local high-class restaurants.
Scandinavian Silver Eel Farm
Scandinavian Silver Eel (SSE) is a
Swedish eel farming company producing eels for consumption,
restocking and ongrowing. The farm was set up by Kemira
Kemi AB, a chemical company based in Helsingborg,
and the industrial town's biggest employer. SSE imports
young eels by air principally from England and upon
arrival in Helsingborg, are placed in quarantine.
During a quarantine of several weeks the eels are
carefully examined for diseases and viruses. Once
in the eel farm, they are given feed made of high
quality marine fish meal and fish oil, with added
vitamins and minerals, using computer controlled equipment.
SSE began life as a waste energy project
in the mid-80's to exploit warm salty cooling water
produced by three sulphuric acid plants. The abundant
quantities of water available meant that farming eels
using a through-flow system at 25 ºC was economically
practical proposition because at this temperature
the eels grow to consumption size within 18 months.
Successful trials during the 1980's
resulted in the construction of a proper commercial
plant. When the chemical plants closed down however,
the eel farm faced closure. Without the warm waste
water, it would not have been economical to heat fresh
water to the required temperature in a through-flow
system. Instead they redesigned the farm as a closed
re-circulating system, keeping the energy needed to
heat the water to a minimum.
Recirculating Aquaculture Systems
(RAS)
Traditional aquaculture production
in ponds requires large quantities of water. Approximately
1 million gallons of water per acre are required to
fill a pond and an equivalent volume is required to
compensate for evaporation and seepage during the
year. Recirculating aquaculture systems offer an alternative
to pond aquaculture technology. Designed to conserve
both land and water resources, recirculating systems
can be located in areas unsuitable to open pond culture.
Operators have a greater degree of control of the
fish culture environment, can grow fish year-round
and the crop can be harvested at any time. Recirculating
systems additionally use a fraction of the water required
by ponds to produce similar yields, and remove ammonia
and other waste products.
All aquaculture production systems
must provide a suitable environment to promote the
growth of the aquatic crop. Critical environmental
consideration needs to be given to concentrations
of dissolved oxygen, un-ionized ammonia-nitrogen (extremely
toxic to fish), nitrite-nitrogen, and carbon dioxide
in the water. Nitrate concentration, pH, and alkalinity
levels within the system are also important. To produce
fish in a cost-effective manner, aquaculture production
systems must maintain good water quality during periods
of rapid fish growth. To ensure such growth, fish
are fed high-protein diets ranging from 1.5 to 15
per cent of their body weight per day depending upon
their size and species.
SEE Farm
In order to compensate for the loss
of free energy waste water, SSE altered the existing
farm from a through-flow system using salty water to
a recirculated system using freshwater. The initial
step was to connect the fingerling unit (40 tanks at
2 metres X 2 metres) to a separate trial recirculation
system. After leaving the tank, water is first mechanically
filtered in a drumfilter, then biologically filtered
and finally oxygenated before being pumped back to the
fish tanks. The sludge, faeces and any feed waste collected
during mechanical filtration is then used as a fertiliser.
The biological filtration (nitrification) process
occurs in concrete tanks filled with water, where
small plastic rings are kept in motion by strong aeration.
After installing the recirculation system in the fingerling
unit, the growth and feed conversions were significantly
improved despite having higher stocking levels.
The success of the trial recirculation
system meant that a second system was installed. The
standing stock of SSE now varies between 80-90 tonnes
and the production of consumption of eels is approximately
150 tonnes/year.
Eel Farming
The majority of the world's current
eel cultivation, of more than 130,000 tonnes a year,
occurs in Asia, with significant production in Europe
as well Asian countries, especially China and Japan,
enjoy eating eel for its tonic effect. In Europe,
eel farms can be found in countries such as Sweden,
UK, Netherlands, France, Spain, Denmark and Greece.
Due to the complexity of its lifecycle no one has
yet managed to successfully breed eels in an artificial
environment. Instead, the aquaculture industry relies
on using young eels returning from the Sargasso Sea
to grow.
Eel culture or farming involves catching
juvenile (glass) eels when they enter freshwater and
growing them to a marketable size. The three main
techniques for culturing eels include the use of ponds,
accelerated temperature facilities, and recirculating
systems. The United Kingdom, Italy, France, Germany,
and Australia also culture eels in saltwater. The
main advantage of saltwater eel culture is that the
natural sea salt gets rid of any fungi and parasites.
Eels
Eels are a common kind of freshwater
fish and there are some 20 different kinds of eels.
Mainland China, Taiwan, Japan and South Korea, are
major eel farming areas, but eels are also farmed
in Europe. Eels have a complex reproductive life-cycle.
Eels are known as catadromous - that is, they live
in freshwater but migrate to the ocean to breed.
The European freshwater eel, anguilla
anguilla, is truly one of nature's fascinating life-cycles.
Mature European eels must swim against the Gulf Stream
for 9 months to reach the spawning grounds in the
Sargasso Sea north of the West Indies. The eel larvae
produced by spawning eels drift with the Gulf Stream
across the Atlantic and back to Europe. Here the larvae
go through a metamorphosis and become almost transparent,
hence the name 'glass eels' (also known as elvers),
which are capable of reaching rivers and lakes.
Swimming into rivers and up into the
freshwater, they spend the next 6 - 20 years feeding
and growing into the eels that everyone knows. At
this stage they are known as yellow or brown eels
but in fact could also be a shade of blue, green or
even red. They feed on a wide range of foods preferring
fish and invertibrates, are mainly nocturnal feeders
and during winter months become inactive if the temperatures
are low. Growth is determined by the availability
of food, the average ambient temperature and stock
density. In the lower reaches of rivers where the
stock density is high, eels are small and predominantly
male. Further up rivers where the stock density is
lower, large females are predominant.
As eels reach maturity, the eyes become
bigger, the head broader and the fat content increases.
The undersides of the skin turn silver or bronze and
hence they are known as silver eels. This change prepares
the eel for its journey back to the sea. When conditions
are right, the eel makes its way down the rivers assisted
by the current, and out to sea to begin its long swim
back to the breeding grounds of the Sargasso Sea.
However, this is largely a theoretical assumption
as there is no scientific evidence to prove that eels
swim back that far.
Eel Parties
Towards the end of August in Sweden,
the sky begins to darken. In the rivers of the south,
the eels begin their own journey to the Sargasso Sea.
Eventually, the skies grow so dark that the eels can
no longer see the fishing nets, and they are easily
caught. In Sweden, there can be only one way to mark
such a phenomenon - an eel party. Similar in spirit
to the crayfish parties, eel parties feature eel as
the main delicacy, and it is served smoked, grilled
or stuffed. Restaurants usually hold contests to see
who can lift the most live eels out of a barrel, crowning
the winner the "eel king."
Eel Recipes
The Pirate's Favourite Sandwich
1 person
2 slices coarse brown bread
1 smoked eel fillet
butter
white pepper
sweet/strong mustard
slice of mature cheese
Instructions:
Butter one of the slices of bread and cover it with
an eel fillet seasoned with a little white pepper.
Butter the second slice. Place it on the eel fillet
butter-side up and cover with a slice of cheese that
has been spread with mustard. Place in the oven at
175 ºC for 5 min or until the cheese melts.
Swedish Eel Sandwich
1 person
1 smoked eel fillet (30-40g)
1 egg
1 dessert spoon of single cream
salt and pepper
slice of dark bread
Instructions:
First make scrambled eggs by whisking the egg and
cream together and then placing the mixture in a saucepan
on a low heat. Keep moving the mixture until the correct
consistency is reached. Place the scrambled eggs on
a buttered slice of dark bread. Cut the eel fillet
into 2-3 pieces and place on top of the scrambled
eggs. Garnish with chives or dill and eat while the
scrambled eggs are still warm.
Fried Eel with a Piquant Sauce
4 people
INGREDIENTS:
1 kg fresh eel
flour
savoy cabbage head
15-20 nadin potatoes or similar
3 red apples
capers
SAUCE:
1 hard boiled egg yolk
1 raw egg yolk
1 tablespoon lemon juice
1 teaspoon sweet mustard
1/2 teaspoon salt
200 ml whipping cream
salt and pepper
50 ml finely chopped dill
Preparation:
Cut the eel into 4 or 8 pieces and coat with flour.
Add salt and pepper. Cut the potatoes and apples into
segments. Separate the cabbage leaves and cut away
the stem. Fry the eel pieces in butter until they
have a crispy surface. Fry the potatoes until they
begin to be soft. Add the cabbage and apples. Adjust
seasoning. The sauce is prepared by mixing the cold
cooked and raw egg yolks together in a bowl. Add lemon
juice, mustard and dill. Whip the cream and add to
the mixture. Adjust the seasoning with salt, pepper
and possibly more lemon juice.
For more information on the SEE eel
farm, please contact:
Scandinavian Silver Eel
P.O. Box 902
SE-251 09 Helsingborg
Sweden
Tel. +46 4214 2433 (farm);
+46 4221 2619 (quarantine), +46 4217 1000
(office)
Fax +46 4214 3176
Email: farming@silvereel.se
Website: http://www.silvereel.se/
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Websites
www.fishbiology.net/silvereel.html
Eel site from the University of Leiden in The Netherlands.
aquanic.org/beginer/systems/recycle.htm
Information on fish culture in recycle systems.
http://www.aquaponics.com/
A source for information on aquaponics, hydroponics
and aquaculture.
www.ext.vt.edu/pubs/fisheries/420-897/420-897.html
Should You Attempt Fish Farming? Considerations for
Prospective Fish Growers.
www.aquaculture-online.org/recirc.html
Acted workshops, courses and programs on recirculating
aquaculture systems: principles of design and operation
Further Reading
Books from ITDG Publishing
Small-Scale Freshwater Fish Farming:
Agrodok 15
A. van Eer, T. van Schie, A.D. Hilbrands
£5.95, 1996, ISBN 9072746724
Books from the Food and Agricultural
Organisation (FAO)
Handbook of small-scale freshwater
fish farming
V. Gopalakrishnan, A.G. Coche
US$29, FAO, 1999, ISBN: 9251031630
Available to download for free at: www.fao.org/docrep/T0581E/T0581E00.htm
This document is an output from
a project funded by the UK Department for International
Development (DFID) and the European Commission (EC)
for the benefit of developing countries. The views
expressed are not necessarily those of DFID or the
EC.
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