Japanese eel
| Japanese eel | ||||||||||||
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Individual from Anguilla japonica |
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| Scientific name | ||||||||||||
| Anguilla japonica | ||||||||||||
| Temminck & Schlegel , 1847 |
The Japanese eel ( Anguilla japonica , Japanese 日本 鰻 nihon'unagi ) is a species of fish from the eel family ( Anguillidae ). It is considered threatened in its area of distribution. Like the European eel , the animals are popular food fish.
Description, identifying features
The fish are on average 40 cm long. A maximum total length of 150 cm and a maximum weight of 1.9 kg are documented. The animals have 114 to 118 vertebrae. The lower jaw is slightly longer than the upper jaw, the angle of the fish's mouth lies below the rear (body-side: posterior ) edge of the eye. The head length makes up 11.2% to 11.9% of the body length, and it is 3.7 to 4.3 times the length of the upper jaw. The attachment of the dorsal fin is between 9.0 and 13.5% of the total length behind the gills and measured from these. The pectoral fin has a length of 2.2% to 3.7% of the length of the head.
The teeth are small and conical. The teeth of the jaw are in a narrow band. The tooth band on the ploughshare leg is somewhat wider and longer, or at least as long as that of the jaw. All teeth are arranged in structures that correspond to those of the bristles of a card .
The dorsal and anal fins merge with the caudal fin to form a seam. The approaches of the dorsal and anal fins are less than a head length apart. The elongated body is cylindrical near the head and laterally flattened posteriorly. The animals have muted colors with no marbling or spots. There are scales , these are rudimentary, embedded in the skin and arranged diagonally in groups, the groups of scales are at right angles to each other.
The species is considered threatened and the number of sexually mature individuals is decreasing.
Distribution area
Japanese eels live in East Asian waters. The katadromous species is known from Japan , Taiwan , Korea , China and the northern Philippines . In geographical latitude and longitude, the distribution area can be described as 46 ° N - 15 ° N, 105 ° E - 170 ° E.
Inhabited waters are, for young animals and adolescent specimens before sexual maturity, the upper reaches of rivers and mountain lakes. A part of the population also remains in the brackish water area of the coasts and in the sea.
habitat
The inhabited biotopes are climatically subtropical and usually fresh water; the species lives demersal (close to the ground). It has been proven to occur up to a depth of 400 meters. The water temperatures in the habitat are between 4 ° C and 27 ° C.
Way of life
Eggs and leptocephali of the species could be caught in the north equatorial current in the area of the West Mariana Ridge (latitude and longitude: 14–17 ° N, 142–143 ° E) at new moon. At the same time in the same area there was evidence of adult animals that were about to spawn . Hence, it is a plausible hypothesis to refer to the area as the spawning zone of Anguilla japonica . The spawning business presumably takes place between April and August. The water depth in which the animals spawn is presumably in a narrow range of 150-200 meters, just below the upper limit of the local thermocline at 150 meters depth. The mean size of captured Leptocephali was at the minimum near submarine ridges of the West Mariana Ridge. An examination of otoliths of the species showed an average increase in length of 0.5 mm per day. The animals are mainly bound to the north equatorial current and the Kuroshio in their migratory movements .
In terms of calendar, a common chronological sequence of the appearance of glass eels on the coasts can be observed. Sporadic specimens can be found along the northeast coast of Luzon from late October . A higher density of finds can then be found off Taiwan early in November. Another two to four weeks later, the animals arrive off Fujian and the southern Japanese Pacific coast. Zhejiang , Guangdong , Jejudo and the Pacific coasts of central Japan are reached between January and March. Via the southern Jiangsu with the delta of the Yangtze , the South Korean coast and the Japanese east coast (focus of the presence of the glass eels: between February and April) the population then reaches northern Jiangsu and western Korea (peak of the presence: March to May ). Most recently, between April and June, the north Chinese coasts, northwestern Korea and the mouth of the Yalu are reached. Shifts are possible, so in 2010 and 2011 peak values of the glass eel number off central Japan were only observed in June.
Due to the connection to the two ocean currents (north equatorial current and Kuroshio) for the successful completion of the life cycle, the spatially separated small populations of north Luzon, the basin of the Thai Mae Nam Chao Phraya and off Cambodia probably contribute little to the conservation of the species.
Anguilla japonica and man
The Japanese eel is the most expensive food fish in Japan. He is stalked in the age stages of glass eel , yellow eel and silver eel . The fish meat is fresh, smoked , deep-frozen and canned and marketed, preparation methods are steaming , grilling and baking .
The main catching seasons for glass eels off Taiwan are from November to February. Off Fujian and the South Japanese Pacific coasts the focus is from December to February, in Zhejiang , Guangdong , Jejudo and the Pacific coasts of Central Japan the main fishing activity is between January and March, in Jiangsu with the Yangtze River Delta , the South Korean coast and the Japanese east coast between February and April. Later that year, off north Jiangsu and western Korea, the glass eels are mainly fished between March and May, and then between April and June off the coast of north China, northwestern Korea and the mouth of the Yalu .
To support the populations, wild glass eels are caught and used as stock in freshwater or raised in aquaculture for human consumption.
Anguilla japonica is the first vertebrate to have a fluorescent protein discovered in its cells . Such proteins, like green fluorescent protein (GFP), are used as marker molecules in research into biochemical processes. The protein first discovered in the muscle cells of A. japonica and later also of A. anguilla and A. rostrata was called UnaG . It glows green when exposed to blue light and when it is bound to bilirubin . In the eels, it probably acts as a storage or transport protein for bilirubin, which acts as an antioxidant in the muscle cells, which is an adaptation to the extended periodic migrations of the three species. In contrast to GFP, with UnaG the bright fluorescence occurs even at low oxygen levels in the cell. This feature promises to be used in the investigation of anaerobic areas within malignant tumors . So far (as of 2013) it has been shown that UnaG can be used to measure bilirubin levels in human blood serum , although these are potentially simpler and more sensitive and can be carried out with smaller blood samples than conventional bilirubin measurements.
Anguilla japonica catch statistics
Total Japanese eel yield in tons × 1000 as reported by FAO , 1950-2010
Captured in the wild, 1950-2010
Aquaculture production, 1950–2010
Individual evidence
- ↑ a b c Anguilla japonica on Fishbase.org (English)
- ↑ a b c d e f Species Fact Sheets Anguilla japonica (Temminck & Schlegel, 1847) ( en ) FAO , Fisheries division. Retrieved November 28, 2020.
- ↑ a b c d e f g h Anguilla japonica in the Red List of Threatened Species of IUCN 2020-2. Retrieved November 28, 2020.
- ↑ Akiko Kumagai, Ryoko Ando, Hideyuki Miyatake, Peter Greimel, Toshihide Kobayashi, Yoshio Hirabayashi, Tomomi Shimogori, Atsushi Miyawaki: A Bilirubin-Inducible Fluorescent Protein from Eel Muscle. In: Cell. Volume 153, No. 7, 2013, pp. 1602-1611, doi: 10.1016 / j.cell.2013.05.038 ; see also Monya Baker: First Fluorescent Protein Identified in a Vertebrate Animal. In: Scientific American. July 13, 2013, accessed November 29, 2020 .
- ↑ a b c Based on information in the FishStat database , FAO.
