Site Vist to Kindai University

As a part of this "School-of-Tuna" project, we visited the Oshima Station, Aquaculture Research Institute, Kindai University, in which the complete cultivation of bluefin tuna was first successed in the world in 2002 (Date of visit: 24 July 2022).

Complete Cultivation

The complete aquaculture refers to aquaculture that semi-permanently sustains the cycle of collecting eggs taken from farmed adults, hatching them, and raising them to adulthood.
(See For sustanability > Aquaculture

Becouse the complete aquaculture does not utilize natural marine resources, it enable to bring tuna to our table with be recovering natural tuna stocks. Most of aquaculture conducting in current require captured natural tuna fry. It is strongly expected that the complete aquaculture of tuna become more popular to help maintain the richness of the oceans in the future.

History of Complete aquaculture of tuna project in Kindai University

1970

Research into the complete aquaculture of bluefin tuna began.

Kindai University was selected as one of the organizations in charge of the Fisheries Agency's 'Tuna Cultivation Technology Development Test', and the research into the complete aquaculture of bluefin tuna was initiated.

1979

Spawning of bluefin tuna was confirmed and fertilized eggs were successfully obtained.

In 1974, 60 five-year-old fish (weighing about 70 kg) were observed spawning in a cylindrical net fish tank for the first time in the world, and a large number of fertilized eggs were successfully obtained. However, as there was still a lack of knowledge on breeding methods and feed for the fry, breeding of fry hatched from fertilized eggs lasted only 47 days and the total length of the fish was 59.4 mm.

1983

No more spawning of parent fish was observed.

1994

Spawning of 7-year-old fish was again observed.

1995,1996

The fry hatched from fertilized eggs were successfully raised to younglings of 30 cm in length and 300 g in weight.

2002

Complete aquaculture of bluefin tuna was achieved for the first time in the world.

A total of 20 fish, including 6 farm-raised seven-year-old fish and 14 farm-raised 6-year-old fish spawned, and complete aquaculture was achieved.

2004

Complete farm-raised bluefin tuna were shipped.

The bluefin tuna aquaculture project was an unprecedented and difficult challenge. The success of 32 years of research was very impressive, despite some unexpected slumps, such as the tuna not spawning for 11 years.

Location of Oshima Station

The Oshima Station is located at the southern tip of the Kii Peninsula. The fish tanks at the Oshima Station are located in the inner bay, and the road above the sea acts as a breakwater. Therefore, fish cages in the bay are less likely to be damaged by typhoons. The high water temperature and good water quality make it suitable for tuna farming.

Aquaculture cage offshore

Cylinder-shaped net cages are used for tuna. The net cages used for tuna farming at Kindai University have a diameter of 30 m and a depth of 15 m. Tuna swim in circles in the net cages. Tuna take in fresh oxygen by swimming with their mouths open. If they stop swimming, they can no longer take in oxygen. Tuna, therefore, swim all their lives.

Scheme of Complete aquaculture of tuna

capturing eggs in aquaculture cage

Tuna spawn when the water temperature approaches 25°C. At the Oshima Station, the spawning season is from June to August, a little later than for natural tuna, which spawn in April and May.
The fertilized eggs float to the surface of the sea in aquacultuer cage and are collected with a net by hand.

Hatching eggs and growing upto fry

The production of seedlings from hatched larvae (after hatching until fins are complete) to fly (about 20 days after hatching) is a fundamental technology for complete aquaculture.
The process is one of the most difficult, as there are several problems and difficult points, such as the occurrence of cannibalism around 20 days after hatching, when the fish change from hatchlings to fry.

Tranfer to aquaculture cage offshore

This is the process of fly cultured in the land-based tank to transfer into aquaculture cage offshore. This is conducted around July, one month after hatching.
Through this process, 30% of fry die from accidental ingestion, stress, and other factors.

Growing fry to adult fishes in aquaculture cage offshore

This is the process of fly cultured in the land-based tank to transfer into aquaculture cage offshore. This is conducted around July, one month after hatching.
Through this process, 30% of fry die from accidental ingestion, stress, and other factors.

Growing fry to adult fishes in aquaculture cage offshore

The right figure shows specimens of bluefin tuna preserved at Oshima station. Photos in the figure represent respectively specimens of eggs, fry, youngling about 10 cm in length, and youngling 51.6 cm in length. The youngling of rightmost photo is 200 days old and weight 2,484 g in weight.

Feed

For fry and younglings

Feed for fry are Brachionus plicatilis (zooplankton), Artemia, and hatched larvae of parrot fishes, depend on their growth.

Feed for adult fishes

1 year old (taken offshore last July) Body size is 3 kg in weight, 50 cm in length (as same as new born baby of human). About 1,000 fishes present in one cage		Four years old Body sise is 70~80 kg in weigth and 1.7 m in length (as same as adult human male) Fishes of this size are shipped to restrants and other customers.

The compound feed are feeded in aquaculture in Kindai University. The size of the feed varies as it depends on the growth of the tuna. The compound feed are consist of horse mackerel meats and sardine fishmeal meats, vitamins, and other nutrients.

ITuna eat about 3% of their body weight in a day. Therefore, tuna farming requires an enormous amount of feed. It is said that the final amount of feed required before shipment is 15 kg per kg of tuna, which means that more than 1 ton of feed is needed to grow tuna to 70-80 kg, the size for shipment!

Kindai University originally used frozen horse mackerels and sardines as bait, but now feeds tuna with formula feed, except for fry, due to problems with freshness management, food poisoning, and water pollution from leftover feed.

Shipping Complete farm-raised bluefin tuna are shipped 3 to 4 years after birth. When complete farm-raised bluefin tuna are shipped from Kindai University, they receive a 'diploma'.

What percentage of hatched eggs become shipped tuna?

About 10% of fry hatched from eggs are released offshore. Even after releasing offshore, 30% of them die from accidental ingestion, stress, and other factors. Tuna are very delicate fish. Ultimately, only 1-2% of the eggs grow into shipped tuna.

Complete aquaculture of fish other than tuna

Complete aquaculture of Japanese eels has been achieved, but it is still difficult to produce large amounts of them through complete aquaculture. Also, complete aquaculture of conger eels has not yet been achieved.
Furthermore, complete aquaculture has been achieved for yellowtail and amberjack, but the aquaculture industry uses mostly wild juveniles, and the aquaculture has not been replaced by complete aquaculture.

Kindai University tuna has a whole-body toro!?

Kindai University's farmed tuna has more fat than wild-caught tuna and is said to have whole-body toro, why? Main reasons are ・Feed content ・Amount of exercise We had a bowl of Kindai tuna ”Kindai Bluefin Tuna Bowl” for lunch at the Cape Shiono Sightseeing Tower. The tuna was tender and very tasty.

Message from Professor

We received comments from Dr. Yasuo Agawa, who guided us around the Oshima Station, Aquaculture Research Institute, about the future of the sustainable ocean.

Fisheries resources are limited, so it is necessary to use them carefully and without waste, and it is also important to increase them through proper aquaculture. Although aquaculture of fish that are difficult to raise is becoming more successful, we cannot be optimistic about the state of the oceans in recent years. Farming of difficult-to-breed fish species is becoming more successful. We need to utilize carefully and without waste limited fisheries resources and to increase them through appropriate aquaculture. However, the situation at sea over the past few years has been alarming. For example, unprecedented high-temperature seawater came ashore on the Kii Peninsula (it has adverse effects on both young and parent fish), and many pearl oysters have been lost to viral diseases in the past three years. Such cases have been increasing in recent years. Even if fish and shellfish can be produced through aquaculture, we must avoid situations in which we cannot grow them due to the changes in the aquaculture area. The time has come for everyone to seriously consider how to maintain healthy oceans. We need to make efforts to leave healthy oceans for future generations.

Reference

Website of Aquaculture Research Institute, Kindai University
　　https://www.flku.jp/english/

世界初！マグロの完全養殖
　　(translated title: World's First! Complete cultivation of tuna)
　　Publisher：Kagakudojin
　　Auther：Hiroki Hayashi
　　(in Japanese)

究極のクロマグロ完全養殖物語
　　(translated title: The ultimate bluefin tuna farming story)
　　Publisher：Nikkei BP Marketing, Inc.
　　Auther：Hidemi Kumai
　　(in Japanese)

トコトンやさしい養殖の本 　　(translated title: A book about aquaculture that is easy to read)
　　Publisher：Nikkan Kogyo Shimbun
　　Edited：Aquaculture Research Institute, Kindai University
　　(in Japanese)

Home © 2022-2023 マグロの学校/School-of-Tuna All rights reserved.