Complete aquaculture” has already succeeded, but… when will “farm-raised eels” be on our tables? | FRIDAY DIGITAL

Complete aquaculture” has already succeeded, but… when will “farm-raised eels” be on our tables?

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From eggs to adult fish…production cost per fry has dropped to 3,026 yen, but

In recent years, the price of eels has continued to soar. The eels we eat today are fry, or glass eel, collected from eel fry and raised in aquaculture ponds, but the amount of glass eels harvested continues to decline year by year.

It is said that it is difficult to cultivate eels from their eggs, and the only way is to increase the size of the glass eel. Will we no longer be able to eat eels at this rate?

No, it is now possible to harvest eggs in a relatively stable manner, and we are raising glass eels from the eggs.

Yukinori Kazato, an eel farm researcher at the National Institute of Fisheries Research and Education, says, “When will we be able to fully cultivate eels?

I have no idea when fully farmed eels will be on our tables,” said Yukinori Kazato (PHOTO: AFLO).

He has already succeeded in completely cultivating eels 13 years ago by taking more eggs from adult eels raised from eggs and producing artificial seedlings. Now, there is no need to worry. Will we soon be able to eat fully farmed eels?

I have no idea when we will be able to eat fully farmed eels.

He denied it.

When it is reported that the complete cultivation of eels has succeeded, you may think that the eels will be sold immediately, but even if it costs one million yen per eel, it means that the eels have been completely cultivated. However, this does not mean that they can be marketed.

In fiscal 2004, the production cost per fry was 27,750 yen. The production cost per fry in 2004 was 27,750 yen, and in 2008 it was reduced to 3,026 yen, but even so, if 3,000 yen were added to the current price, it would not be easy to put on the dinner table.

Why in the world are production costs so high?

It’s because we make our own food and tanks, and it takes a lot of time and effort to raise them.

Eel hatchlings, called leptocephalus, before they become glass eels. After six months to a year, they metamorphose into glass eels. Since the shape is different from that of the eel, it was once thought to be a fish unrelated to the eel, hence the name.
This is a state called preleptocephalus, about 50 days after hatching (PHOTO: courtesy of the National Fisheries Research and Education Organization).

At first, I had no idea what to feed them…

Methods for raising glass eel have already been established, and eel farmers all over Japan are cultivating them. The research being conducted at the National Institute of Fisheries Research and Education is to collect eggs and grow them into glass eels.

When eels hatch from eggs, they become preleptocephalic hatchlings, which later grow to become leptocephalic eels. When this “metamorphoses,” it becomes a glass eel, which eventually grows into a large eel.

As preleptocephalus, they live off the nutrients stored in their bodies. It is not until the leptocephalus begins to require food that the preleptocephalus begins to need it.

The leptocephalus has a straight digestive tract. They cannot digest or absorb food unless they are fed special food. There are plenty of feeds that they eat but don’t grow, or they eat but die.

In normal aquaculture, the fish are fed on small plankton called rotifers and artemia, but leptocephalus do not eat such things. So they had to make a special bait, but at first they had no idea what to feed them. They tried from one end to the other and arrived at the current feed.

Eels are said to be a mysterious creature. It is said that the reason for the lack of clarity in their ecology and other aspects of their lives makes eel farming a difficult task,

Natural salmon eat insects, but farmed salmon do not contain insects in their food. We have some idea of what nutrients fish need to grow. Even if we don’t know what natural eels eat, we can still make bait.”

What he is feeding Leptocephalus now is a fish meal base, which he sloshes around like loose toothpaste. Leptocephalus are baby eels, so they can’t eat a lot at once. They are fed five times a day. The sloped food gets on the walls of the tank, and if left untreated, it can cause bacteria and disease, so the tank is cleaned five times a day. It really takes a lot of time and effort.

The baby bait has a long life span of 150 to 300 days. The longest period, which is five to ten times longer than that of other fish, is also a factor that makes eel culture difficult.

The tanks must be cleaned five times a day to prevent the eels from getting sick from bacteria. A new tank is currently under development (PHOTO: courtesy of the National Fisheries Research and Education Organization).

As for egg harvesting, we make hormones and inject them into the eels.

Furthermore, eels do not mature even after they grow up, he said.

Salmon, for example, sense the seasons and mature at the appropriate time. However, if they are kept in dark conditions all the time or at inappropriate water temperatures, they do not mature. They don’t produce eggs or sperm. Some environmental factor is necessary for them to mature, but in the case of eels, we don’t know what that is.”

They did everything they could think of, including water temperature and brightness, but they couldn’t figure it out. The result,

“We gave up. As for the eggs, we made hormones and injected them. It’s the same as treating infertility in humans. This has enabled us to get eggs in a stable manner.

In 2009, it was discovered that the spawning site of eels was near the Mariana Islands, which had been unknown for a long time. However, the discovery of the spawning grounds did not bring about any dramatic changes in aquaculture.

The idea that once we know the ecology, we can do something about it is wrong. For example, if eels spawn at a depth of 500 meters, you cannot build a tank that is 500 meters deep. On the contrary, there are things that can be done without knowing the ecology.

I had thought that the reason eel cultivation is not easy is because there are many mysteries about their ecology, but this does not seem to be the case.

The domestic requirement for “shirasu eels” is 100 million!

Thanks to the tireless efforts of researchers, the production cost of one eel is now about 3,000 yen. Do you think it will be possible to produce them more cheaply in the future?

Special bait, special tanks, and special breeding methods. Eel farming is expensive. It is impossible to produce them cheaply.

The reason why the production cost has decreased from less than 30,000 yen in 2004 to 3,000 yen is because the survival rate of eels has increased that much. If we can catch 100 eels instead of the 10 we used to be able to catch, the production cost per eel will go down. That is how it works.

Currently, only 3 to 5% of the eggs turn into glass eels. This figure is not inferior to that of other fish.

If we work hard at this laboratory, we can farm 30,000 to 50,000 eels a year. However, the number of glass eels needed by eel farms nationwide is 90 to 100 million. There is still a large gap.

We would like to devise feed, tanks, and rearing methods to bring the production cost down to about 1,000 yen per eel, and if possible, a little lower, so that we can get them on the dinner table as soon as possible. We are working hard every day to achieve this goal.

The Japanese eel was already listed on the IUCN Red List of Threatened Species 1B in 2002, and is considered to be at high risk of extinction in the wild in the near future. The harvest of glass eel is also restricted. One can only hope that fully farmed eels will make it to dinner tables before harvesting is banned.

Kazato specializes in fish reproduction. The hormones that bring eels to maturity can be applied to other fishes as well,” he said. It will also be useful in the future when we start cultivating conger eels, which belong to the same order as eels.

Yukinori Kazato is Director, Fisheries Research and Education Organization, National Institute of Fisheries Technology (Nansei), Japan. In 2008, he received the Fisheries Science and Technology Award for his research on “the advancement and application of artificial heat and egg collection techniques using eel gonad-stimulating hormone.

  • Reporting and writing Izumi Nakagawa

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