Manufacturing & Packaging
Artificial Japanese Glass Eel (Anguilla japonica)
Production in Korea
Abstract
Freshwater eels are very valuable fish species, principally in
Asian and European countries. Over 97% of worldwide eel
production is based on farming of the European eel, Anguilla
anguilla and the Japanese eel, Anguilla japonica. Eel farming
is a capture-based aquaculture activity. It is based on the
practice of collecting juvenile eels from the wild and ongrowing in captivity to marketable size using aquaculture
techniques. Due to their complex life cycle, research efforts
have not yet managed to produce glass eels on a commercial
scale. After a series of efforts, Korea made a breakthrough by
producing two Japanese glass eels in 2012. Several other
phenomenal pieces of research were conducted to produce
the artificial Japanese glass eel, as well as to develop the
complete package for eel aquaculture in Korea.
Introduction
The family Anguillidae, commonly referred to as freshwater
fish, is composed of at 16 species and three subspecies, all in
the genus Anguilla (Tsukamoto, 2009). Anguilla species are
distributed throughout tropical and temperate waters, expect
for the Eastern Pacific and South Atlantic (Aoyama et al.,
1999). The various life stages of all Anguilla species are
harvested and traded on a global scale for farming and
consumption. As catadromous fish, they migrate from rivers
and inland bodies of water to the oceans to breed, and then
the young return to freshwater. For all Anguilla species, the
life cycle is essentially the same (Fig. 1).
Leptocephalus: The oceanic pelagic larval eel, which migrates
from the spawning area to the continental shelf. Narrow,
deep-bodied, shaped like a willow leaf. Glass eel: Small,
transparent juvenile eel formed by metamorphosis of
leptocephalus. Metamorphisis occurs at sea, perhaps near the
edge of the continental shelf. They are not fully pigmented
juveniles. Marine and estuarine habitat. Elvers: Fully
pigmented juvenile eel, with a total length under 30 cm and
less than five years old. Predominantly freshwater habitat.
Yellow eel: Eel residing in continental waters, with a size
generally over 30 cm long and more than five years of age.
This stage typically lasts several years. Predominantly
freshwater habitat. Silver eel: A sexually maturing eel,
migrating to the oceanic spawning area. They usually reach
78 International Animal Health Journal
the mature stage between 10 and 20 years. Marine habitat,
but metamorphosis commences in freshwater.
Japanese eel, Anguilla japonica, is a very important cultured
species in East Asia due to its high market value, desirable
taste and recent supply shortage (Ren et al., 2007). Five major
producers of this species are China, Japan, Korea, Malaysia
and Taiwan. The eel aquaculture industry in these countries
has been growing, e.g. in Korea its production increased from
2739 tons in 2000 to 6766 tons in 2009 (Son et al., 2011). Eel
culture has depended on natural captured Japanese glass
eels, and the highest amount of fishing reached 160 tons (15
tons in Korea) in East Asia in 2006. Recently, the amount of
Japanese glass eel fishing has been gradually decreased and
the value reached 15 tons (one ton in Korea) in East Asia,
2013. Environmental variation, overfishing, climatic changes,
pollution and infections with the swim bladder parasite
(Anguillicoloides crassus) and/or eel viruses have been
implicated as causes for the current decline in the Japanese
glass eel population (Tsukamoto, 2009).
The limited and inconsistent availability of wild broodstock
Japanese eel, as well as early survival rate decreasing in
culture of the tropical Japanese glass eel (Luo et al., 2013)
and the protection or import regulation of Japanese glass eel
resources (Crook et al., 2013) over the last decades, increased
the requirement for artificial eel production in captivity.
Artificial eel production has been studied since the 1960s,
and Yamamoto and Yamauchi first succeeded in producing
Japanese eel larvae in 1974 from eggs obtained from
hormone-treated eels, and Yamauchi et al. (1976) succeeded
in rearing pre-leptocephalus for two weeks. In 2002, the
National Research Foundation of Korea (Korea Research
Foundation) approved the national project on “NRF-2002005-F00002” through the Feeds and Foods Nutrition Research
Center (FFNRC) as the priority research institute at Pukyong
National University, Busan, Korea. This project was the first
official Korean Government Support Project almost from
2002 to 2004. FFNRC successfully produced the artificially
matured male and female broodstock Japanese eel and
fertilised eggs in 2003. This research fund was terminated in
2004, and the National Fisheries Research and Development
Institute (NFRDI) continued this research in 2006 with fund
Volume 2 Issue 3
Manufacturing & Packaging
research from FFNRC, successfully hatching two Japanese
glass eels in 2012. Artificial production technology of
Japanese eels has improved markedly in Korea, and further
studies are necessary to obtain high quality and mass
production of Japanese eel eggs. Additionally, artificial
reproduction of the European eel, Anguilla anguilla (Palstra
et al., 2005), the New Zealand longfin eel, Anguilla
dieffenbachia and the shortfin eel, Anguilla australis
(Lockman and Young, 2000) have been attempted with a
number of research groups.
Fig. 1. Life cycle of eel (Gissurardottir, 2006)
Research on Japanese eel reproduction is complicated,
because broodstock eels stop feeding when silvering in nature.
For example, Chow et al. (2010) found that Japanese eels
caught in the spawning area had not been eating in the
marine phase of the migration. Also in captivity, feeding is
terminated after transfer to saltwater prior to induction of
maturation. Moreover, it is also clear that the availability of
an optimal diet is identified as a crucial factor for the sexual
maturation and reproduction of the Japanese eel. For
Japanese eels, all the qualitative and quantitative
requirements for reproduction have to be met from their body
reserves, highlighting the importance of pre-spawning
nutrition.
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Manufacturing & Packaging
Summary of Research and Development of Japanese Eels
(A. japonica) in Korea
Recent nutrition studies have contributed further to a better
knowledge of the requirements of proteins, lipids, vitamins
and additives for the maturation process in the Japanese eel.
It was shown that the optimum dietary protein (44.3%), P/E
ratio (24.1 mg protein/kJ), linolenic acid (LNA, 0.35~0.5%),
linoleic acid (LA, 0.5~0.65%), vitamin E (21.2 mg/kg), vitamin
C (41.1 to 43.9 mg/kg) in juvenile and (410.8 to 911.8 mg kg1) in broodstock, as well as additives such as quartz porphyry
(0.7%), BAISM (0.5%) and propolis (0.25-0.5%) levels could
be essential for maintenance of normal growth, physiological
function and overall health. Still our knowledge on the
reproduction of Japanese eels remains limited. However, our
previous studies have shown that final maturation in silver
female and male Japanese eels could be induced by weekly
injections of salmon pituitary extract (SPE) and human
chorionic gonadotropin (HCG), respectively. Also, our results
indicated that artificial maturation by hormone treatment
was successful only during the spring to summer seasons in
seawater with low temperatures (10ºC). These results will
provide valuable information for elevation of the artificial
maturation and reproduction coefficient in the Japanese eel.
Future Perspectives:
1.
Emphasis on nutrition of broodstock eels
1.1.
Cost-effective rearing process
2.
Domesticate broodstock in captivity
3.
Feed development for larvae
4.
New feed development for larvae
5.
Rearing larvae in captivity
6.
Selective breeding for better growth and survival
7.
Disease prevention (e.g. vaccine development)
8.
Conservation of eel resources in the wild
References
• Aoyama J, Mochioka N, Otake T, Ishikawa S, Kawakami Y,
Castle P, Nishida M and Tsukamoto K. 1999. Distribution
and dispersal of anguillid leptocephali in the western
Pacific Ocean revealed by molecular analysis. Marine
Ecology 188, 193-200.
•
Chow S, Kurogi H, Katayama S, Ambe D, Okazaki M,
Watanabe T, Ichikawa T, Kodama M, Aoyama J, Shinoda
A, Watanabe S, Tsukamoto K, Miyazaki S, Kimura S,
Yamada Y, Nomura K, Tanaka H, Kazeto Y, Hata K, Handa
T, Tawa A and Mochioka N. 2010. Japanese eel, Anguilla
japonica do not assimilate nutrition during the oceanic
spawning migration: evidence from stable isotope
analysis. Marine Ecology Progress Series 402, 233-238.
•
Crook V and Nakamura M. 2013. Assessing supply chain
and market impacts of a CITES listing on Anguilla
species. TRAFFIC Bulletin 25, 24-30.
Lockman PM and Young G. 2000. Induced spawning and
early ontogeny of New Zealand freshwater eels (Anguilla
dieffenbachia and Anguilla australis). New Zealand
Journal of Marine and Freshwater Research 34, 135-145.
Luo M, Guan R, Li Z and Jin H. 2013. The effects of water
temperature on the survival, feeding and growth of the
juveniles of Anguilla marmorata and Anguilla bicolor
pacifica. Aquaculture 400-401, 61-64.
Palstra AP, Cohen EGH, Miemantsverdriet PRW, van
•
•
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Ginneken VJT and van den Thillart GEEJM. 2005. Artificial
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•
Ren T, Koshio S, Ishikawa M, Yokoyama S, Micheal FR,
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Son MH, Kim KW, Kim KD and Kim SK. 2011. State of
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•
Dr. Erfan Shahkar, Nutritionist, Blue Aqua
International Pte Ltd. After finished his Master of
Science on Fish Nutrition, Department of Natural
Resources Science, University of Lahijan, Iran. He
continue studied and finish his Ph.D. in the same
major from Department of Marine Bio-Materials
and Aquaculture, Pukyong National University,
South Korea. Dr. Erfan recently join Blue Aqua International Pte
Ltd. on July, 2015 as Nutritionist. His expertise in Fish nutrition
will help all farmers on the problem for highest benefit for the
Aquaculture.
E-mail: erfanshahkar@yahoo.com
Hyeon Ho Yun, Ph.D., Fisheries Science at
Pukyong National University (PKNU). Current
position, Researcher (Ph.D)
at Department of Fisheries Biology/Feeds and
Foods Nutrition Research Center (FFNRC) Pukyong
National University (PKNU).
Email: yun841007@nate.com
Dr. Rungtiwa Piamtongkam is now working
as Regulatory affairs and technical support for
Blue Aqua International Pte., Ltd. after finished
B.Sc. Biochemistry and M.Sc. Biotechnology from
Faculty of Science, Chulalongkorn University,
Thailand. She continues studied and got her Ph.D.
in Microbial and Enzymatic Engineering from
INSA de Toulouse, France in 2010. Recently, she uses her skill on
communication and networking to hand on news and technology
to aqua-culturist via social media and supporting customer in the
industry worldwide.
Email: rungtiwa@blueaquaint.com
Sungchul Charles Bai, Current position,
Undergraduate and Graduate Faculty, Pukyong
National University Professor/Department of
Marine Bio-materials and Aquaculture, and
Director/Feeds and Foods Nutrition Research
Center (FFNRC) Busan 608-737, Korea (82-51)
629-5916
E-mail: scbai@pknu.ac.kr or sccbai@gmail.com
Volume 2 Issue 3