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Genetic research on bluefin tuna is in steady progress

Interview with Dr.Motohiko Sano, Director,
Research Center for Aquatic Genomics,
National Research Institute of Fisheries Science, Fisheries Research Agency

Q: First, I would like to ask you how we should understand the genetic research on fish.
SANO: There is nothing special about this field of study because genes can be found in all living organisms.
Genes are a blueprint of all life. DNA (deoxyribonucleic acid) is, so to speak, a chemical substance that writes that blueprint. Chromosome is like a book that integrates various blueprints of life. Recently, the word “genome” is often used. Genome means genes that are comprised in organisms; in other words, it means the entire genetic information. Some scary image may hang around genetic research as though it appears to be touching on the information on life that we should not see. But that is not true. The research now being conducted on fish doesn’t intend to artificially modify genes–a blueprint of life– by humans. It is the research to find genes from the whole genome sequences and to try to make the extensive use of the information for the benefit of aquaculture, stock management and other purposes.

Q: What is the merit of knowing the genetic information?
SANO: Let’s take the example of livestock. Humans have developed livestock having beneficial characteristics for them by selecting the individuals through generations of crossbreeding and making animals that, for example, can produce more meat and are more resistant to diseases.
In this process, the parents seemingly having excellent characteristics were crossbred in many ways and were made to breed their offspring. After the offspring, bred in this way, grow up, the individuals that seem more excellent are further crossbred. Selective breeding is advanced in this manner through accumulation of crossbreeding in a span of several tens or hundreds of years. By analyzing genetic information, the characteristics of the individuals, which could not be known by appearance, will come to be known clearly, and excellent individual groups having characteristics desired by humans can be produced with minimum crossbreeding using genetic information.

Q: How can this technique be applied effectively to tunas?
SANO: For example, wild Pacific bluefin tuna migrating in the near-shore area of Japan is still in stable stock conditions. Stock management of this species have been launched with the aim to conserve and use them sustainably.
Genetic research is useful in supplementing such efforts to manage the stock. What I mean is that, in the case of tuna farming–expanded actively in recent years–, juvenile tunas caught in the wild are reared in net cages until they become marketable sized- fish. Studies are also advanced on closed cycle breeding system, that is, growing adult tunas from the eggs which were spawn by captured tuna.
Under the current circumstances, however, bluefin tuna farming still relies on wild juveniles.
Closed cycle breeding has been achieved in the limited institutions, but it has not yet reached the practical stage in the aquaculture industry. In the wild, a tuna grows into a parent fish in three years at the earliest, but in farming it takes as long as five years. The efficiency of breeding will improve drastically if the period to maturity is shortened.
It is in this respect that the use of genetic information will contribute to tuna farming. If we develop some genetic DNA marker of tuna linked to early maturation, and select such parents from among a large number of tunas to crossbreed, it is possible to make tuna matured in three years. If the number of tunas that can reach maturity in a short span of time and spawn eggs increases and seedling operation succeeds with higher survival rate, then we can secure the necessary number of individuals for farming without catching juveniles in the wild. As a result, it will become possible to reduce fishing pressures on the wild stocks, thus enhancing conservation of natural resources.
The same principle applies to developing tuna which are highly resistant to diseases and have high-quality meat.

Q: What kind of research is your division promoting now?
SANO: As the only research institute specializing in fisheries in Japan, the Fisheries Research Agency has been promoting from early times the genetic research on the tuna, which is one of highly important fishery resources for Japan. In 2009, the agency introduced the most advanced sequencing device called the “nextgeneration sequencer,” and succeeded in the genome analysis of bluefin tuna. Since fiscal 2011, we launched new research project, commissioned by the Fisheries Agency, the Government of Japan. In the genetic studies, we are trying to find genes that may determine the period of first maturation, faster growth rate and resistance to diseases from the genome. We were able to study that because we had already completed the general analysis of the draft genome sequence of the Pacific bluefin tuna. This research is now drawing attention of scientists in the field all over the world.

Q: Will that research require large amount of efforts?
SANO: Analysis speed improved dramatically after the installation of the next-generation sequencer in our division. The flourishing genetic research throughout the world in recent years owes greatly to the development of this device. The technological level of the sequencer has been upgraded year by year, and the analysis speed will become even faster in the days ahead. The sequence of bluefin tuna genome will be made clear by combining enormous amount of data coming from the sequencer.
This is a work requiring huge amount of efforts using computers. It is not an easy work to find out the precise genes which account only for a several percentage of the genome. But at the same time it is a fascinating work because it is an undertaking we have launched for the first time and it provides new discoveries continuously.
It is really worth advancing this work because it opens up many ways of use and possibilities if the accurate genome organization, blueprint of the bluefin tuna, is made available.

Q: Will there be no need to use wild tunas if the genetic research advances and tuna farming is practiced actively?
SANO: It is quite probable that productivity in tuna farming becomes very high when genetic research on bluefin tuna makes progress. I believe the speed of commercialization will be accelerated because we are promoting the project in coordination with private enterprises. Wild tunas have their benefits while farmed ones have also their own advantages. I think both will coexist by supplementing each other. Therefore, sustainable use of wild resources will assume a greater importance in the future. In other words, the importance of using wild tunas will remain solid. In order to use the natural stocks on a sustainable basis, I think it is important to establish closed cycle breeding system as soon as possible by using genetic information positively so that there may be no catch of juvenile tuna for farming to the extent that it would adversely affect the stock itself.

To know more about the Fisheries Research Agency,
please visit http://www.fra.affrc.go.jp