韓國的鰻魚人工繁殖

Artificial Japanese Glass Eel (Anguilla japonica) Production in Korea 
(http://animalhealthmedia.com/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 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-2002- 005-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 fuund 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.

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.

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 kg- 1) 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

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