News Letter Vol.9
Kinki University 21st Century COE Program English Site > News Letter Vol.9
21st Century COE Program 'Center for Aquaculture Science and Technology for Bluefin Tuna and Other Cultivated Fish'
A detailed introduction to and the current status of the research activities of the Food Safety, Processing, and Animal Feed Group

Masashi Ando (Food Safety, Processing, and Animal Feed Group, Graduate School of Agriculture)

The Food Safety, Processing, and Animal Feed Group consists of 11 persons, including a teaching staff of four, including two at the Fisheries Laboratory Uragami test site and two at the Graduate School of Agriculture, two COE doctoral researchers, five graduate school doctoral course students, and two graduate school masters course students. What characterizes the Group is a high percentage of foreign students and the two COE doctoral researchers are from South Korea and Bangladesh and three of the graduate school doctorate course students are from Malaysia, South Korea, and Bangladesh. Our Group's research themes can be divided into three as the group name suggests.

(1) Development of formula feed for cultured bluefin tuna:
Red sea bream and yellowtail are cultured with formula feed, while bluefin tuna is cultivated with mackerel and other living feeds. One of the reasons for this is that formula feed is not preferred or digested well by bluefin tuna. Thus, in the studies conducted so far, we have identified feed promotion substances to increase their preference and highly digestible sources of protein (Japanese Unexamined Patent Application No. 2006-223164) and are now trying to develop more practical formula feed by improving the research results. As bluefin tuna's nutritional demand and digestion/absorption process have not been fully elucidated yet, accumulating basic knowledge related thereto is essential to the development of formula feed and we are now studying their demand for protein, fact and glucide and the characteristics of digestive enzymes.

(2) Enhancement of the safety of cultured bluefin tuna:
It is known that mercury accumulates much in tuna. The reason is believed to be that tuna accumulates high concentrations of mercury through bioconcentration. When we fed horse mackerel with low mercury content from fiscal 2006 to 2007, we successfully produced bluefin tunas which have lower mercury content than cultured ones fed with mackerel and are continuing to breed bluefin tuna this way (Japanese Unexamined Patent Application No. 2006-84146). We also improved the mercury content test method using the fin, the blood, and other wastes, which method can be applied to the quality control of wild bluefin tuna (Japanese Unexamined Patent Application No. 2006-84147). We also collect fish feeds from around the country and investigate variance in their mercury content between the regions and between the seasons in order to establish methods for selecting safer feeds.

(3) Improvement of the flesh quality of cultured bluefin tuna:
No research has been conducted on the flesh quality of fully cultured bluefin tuna. In a fiscal 2004 COE research, we verified that the amount of glycogen content in the flesh of fully cultured bluefin tuna is related to the speed of flesh coloring. In fiscal 2005, we found that the flesh color retention period can be extended by a six-day fast before landing and in fiscal 2006 we found that a two-day fast is enough to achieve this objective. People at central wholesale markets determine the amount of fat and other quality by visually studying the cutting sections of the tail and the abdomen, so they need to be highly experienced and sometimes make mistakes. If we can determine flesh quality without harming tuna, it would be beneficial to the producers and the distributors. We are now conducting research on a near-infrared analysis method, which is one of the non-destructive analysis methods, for analyzing general ingredients, glycogen content, the K value, the metmyoglobin formation rate, etc.

Achievements of the cross-group research project

Wataru Sakamoto (Cross-group project member, Fisheries Laboratory)

Introduction: When the Kinki University COE Project was adopted in 2003, four research groups were organized to conduct researches. However, many research themes remained which should be solved by the cross-sectional activities of multiple research groups. Thus, a cross-group research project was established, combining the special methodologies used by the research groups. The behavioral analysis researchers of the Source Dynamism Group were assigned to make measurements and analyses related to

(1) the size of the preserve and the swimming of tuna,

(2) the feed digestion and absorption process as viewed from the changes in the temperature of the abdominal cavity,

(3) the impact of environmental changes upon bluefin tuna in preserves, and

(4) the swimming behavior of cultured bluefin tuna after re-release into the sea

in cooperation with the Seedling Production and Culture Group. The density and school swimming behavior would be helpful to the Seedling Production and Culture Group in determining the size of a preserve. The amount of feeding, digestion and absorption, and changes in behavior due to environmental changes in the preserve may also provide important information to them. Furthermore, cultured bluefin tuna's regression to natural sources after release into the sea is expected to become a big issue for the entire marine products industry in Japan and thus has been taken up as a theme of interest. Now, I would like to give an overview of major achievements on the subjects already reported in this News Letter.

(1) The size of the preserve and the swimming of tuna
We measured bluefin tuna's swimming depth, tailfin oscillation, and swimming posture in a large preserve (having a diameter of 35m and a depth of 23m) and in a small one (having a diameter of 16m and a depth of 13m) using acceleration data loggers. A calculation of the swimming speed of bluefin tuna in the two preserves based on the records of tailfin oscillation obtained by the acceleration data loggers showed that bluefin tuna in the large preserve swam faster at night, whereas those in the small preserve swam at the same speed all the day. No change was observed during the day in the swimming posture of bluefin tuna in the large preserve, whereas that of bluefin tuna in the small preserve significantly changed at night. It is assumed that bluefin tuna in the small preserve avoided colliding against the net preserve by constantly adjusting their swimming speed and posture at night. It was expected that living in the small preserve was more stressful, affecting growth, flesh quality, and the amount of feeding. These issues are being analyzed by another research group. With respect to preserves, it is necessary to clarify the relationship between the best size of space necessary for swimming and the size of each fish and the number of fish contained therein. Figure 1 shows the roll angle in the small preserve.

(2) The feed digestion and absorption process as viewed from the changes in the temperature of the abdominal cavity
Figure 1. Frequency distribution of the roll angle of bluefin tuna in the small preserve

Zero degree refers to the median position and the body roll is shown as an angle.
The temperature of the abdominal cavity of bluefin tuna is kept higher than the ambient temperature. This temperature varies depending on whether the fish is feeding or on fast, as well as according to the amount of feeding and the type of feed. It seems that the amount of feeding affects the time for which the abdominal cavity temperature remains high, while the type of feed affects the temperature rise early in the feeding period. If we can obtain these information real-time, we can know the feeding status every day and it will be helpful for fish health control. We recorded the abdominal cavity temperature, giving four different types of feeds (squid, horse mackerel, sand lance, mackerel), each for about one month. We found that the temperature increase after feeding was largest for squid, followed by horse mackerel, mackerel, and sand lance. We are now making analysis to identify the cause of this difference. We also have a plan to attempt an analysis of the process of digesting and absorbing artificial feed that will be developed in the future, from changes in the abdominal cavity temperature.
Figure 2. Change in the abdominal cavity temperature after taking 1.1kg of different kinds of feed. Time after feed on the horizontal axis. Significant temperature increases are observed after feeding squid.

(3) The impact of environmental changes upon bluefin tuna in preserves
Environmental changes are a critical issue for the fish living in a preserve from which they can not escape. An issue of interest is how the fish endure changes in the marine environment, such as typhoons involving heavy rains and surges. This section gives an overview of the changes in the swimming depth and abdominal cavity temperature and death of bluefin tuna in preserves due to typhoon No. 18 which hit the Amami region in September 2004. Keten, where the culture site is located, was subjected to torrential rains from September 5 to 7. Prior to the arrival of the typhoon, records taken from the data loggers implanted in the fish showed that they were swimming at all depths, from surface to bottom. The typhoon hit Amami-oshima on September 6 and swimming depths began to converge upon a middle level of 15m or so in the afternoon of the same day. The tuna swam only at the surface from the midnight to the morning of September 7. They lied down on the bottom in the afternoon of the same day, being exhausted. It is found that the fish stayed at the middle layer after the arrival of the typhoon to escape from water clouding at the bottom layer, net 'Blowing' due to strong bottom-layer currents caused by surges, and the surges and inflow of low-salt, highly clouded water at the surface due to rains. Later, the fish came up to the surface to breathe, but died in the end. The abdominal cavity temperature dropped sharply just before death. It is necessary to analyze these information and study the net preserve installation place and the seabed environment.

Figure 3. Bluefin tuna's abdominal cavity temperature before and after the arrival of typhoon No. 18

(Shown by the two solid lines in the upper part of the lower figure. Water temperature is indicated by an underline in the lower figure and the swimming depth is shown by dots in the upper figure.)

(4) The swimming behavior of cultured bluefin tuna after re-release into the sea
Figure 4. Trace of the horizontal movement of BT1 obtained by ship tracking
As mentioned above, cultured bluefin tuna live in a closed space. If they are released to the ocean where there is no obstacle, can they return to the wild and survive to catch feeds and swim around? With a view to solving this question, we released 25 fish, which were caught when young and were later bred in a preserve for 80 days, into sea waters and keep track of them by an ultrasonic transmission/receipt system. The caudal furca length ranged between 40cm and 52cm and we implanted ultrasonic transmitters in the abdominal cavity of four of them. We tried to keep track of one on a ship equipped with a receiver and arranged to record the ID and receipt time for the other three with four receivers installed at the Keten Bay. Figure 4 shows an example of tracking by the ship. On the day of release, we could track the tagged one for six hours, finding that it swam around in the bay at a speed between 2km and 4km per hour and came back close to the preserve at the feeding time, 3:00 p.m. However, on the next day, when we tried to keep track of it again, we immediately lost track as it swam faster than the ship, which was sailing at 10km per hour. Cultured bluefin tuna swim at the same speed and depth as in the preserve immediately after release, but seem to get accustomed to the natural environment in one day. This trend is also reported to have been observed with Japanese tilefish, and our research results are valuable. We were provided with 25 fish for the first attempt, but in order to obtain accurate results, we need to release hundreds to thousands of seedlings and study the movement route and the growth process.

The series of researches were conducted by biotelemetry, attaching or implanting small recording/transmission devices to or into bluefin tuna. This method is used mainly to study the behavior of marine lives in the natural environment. It is a new attempt to apply biotelemetry to the collection of information on the behavior and body of fish in a preserve which cannot be grasped otherwise, for use in culture. Much of the attempt was made to solve the issue presented by the Seedling Production and Culture Group. So far we have obtained only fundamental information, but we think we could provide data required by the Seedling Production and Culture Group. It is necessary for us to scrutinize the results together and develop a method for solving the problem. We are exploring the possibility of solving another pending issue, that is, the identification of parent fish and the predication of the time for their oviposition, by behavioral analysis. For this end, it is necessary to continue the cross-group project.

Report on Science Cafe @ Kindai COE 2nd Session — Safety and Security of Tuna Flesh —
At Ashibi-no-sato in Nara Town, on September 30, 2006

Erina Nagata, COE Doctoral Researcher (Environmental Conservation and Source Dynamism Group, Graduate School of Agriculture)

The second session of Science Cafe @ Kindai COE was held on September 30. This time, the teachers and graduate students of the Usage Group talked about topics related to seafood. The program consisted of three parts, the provision of topics, table discussion (about solutions), and examples of solutions.

The topics provided at Part 1 included (1) 'The taste and functionality of fatty tuna and problems with tuna flesh (color)', (2) 'You are surrounded with plenty of mercury', and (3) 'Do you know cadmium is accumulated in the internal organs of squid?' All the participants listened carefully to the lectures under these somewhat shocking, and at the same time attractive, themes. After the lectures were over, COE doctorate researchers, graduate students, and other supporters sat at the tables, discussing briskly with the participants. A participant said 'I thought generally natural ones are more valuable than cultured ones, so I was very surprised to hear that mercury content is lower in cultured bluefin tuna'. At the Cafe, Kindai bluefin tuna was offered and the participants had brisk discussions, enjoying the good taste of it. At Part 3, the lecturers talked about some of the researches that Kinki University has been conducting to solve the problems with seafood discussed at the preceding parts. Some of the questions and opinions advanced by the participants related to the researches which have actually been conducted by the other research groups of Kindai COE, and we felt that the perspective of the general public is close to that of the COE, which focuses on practical sciences.

The general audience was somewhat small, ten persons, but just because of this, the supporters felt closer to and talked with the participants in a relaxing atmosphere. In the questionnaire sheets collected at the end of the session, many participants replied 'I want to come again', 'This session was very instructive', 'I want this unique program to be continued', so the staff felt relieved. Please visit the website of Science Cafe @ Kindai COE for the further details of the second session, the results of the questionnaire survey, the schedule of the next session, etc.


Report on Science Cafe @ Kindai COE 3rd Session — Breeding fish for research —
Tearoom of the Kinki University Graduate School of Agriculture, on October 28, 2006

Naomi Yagishita, COE Doctoral Researcher (Seedling Production and Culture Group, Graduate School of Agriculture)

The Science Cafe 3rd Session was held at the tearoom on the second floor of the School of Agriculture campus log house. That day, the School of Agriculture held a special open-day, so we had an audience of as many as 25 people for Science Cafe, including high school students and their parents visiting the campus.

The first theme was 'Incubating the eggs of bluefin tuna' and the second one was 'Breeding larval eel'. The participants, who may often eat these fishes, were taught that it is very laborious and difficult to incubate their eggs and the Kindai COE is engaged in leading researches on the breeding of these fishes. The third theme was 'Effort to conserve rare fishes', especially Itasenpara Bitterling, a protected animal. The lecture given by the researcher who is actually working to protect this species was very persuasive and had great appeal to the participants as he taught that this species is endangered even in the well-known River Yodo. It seemed that all the lectures were of great interest to the participants, who listened to the lectures very closely. After a break following the third lecture, we held discussions over tea at each table. Conversations were brisk at every table. At the general discussion session, the supporters advanced the questions raised at each table to the lecturers, but there wasn't sufficient time to answer all the questions. At some tables, discussion continued even after the Cafe was closed, showing that the participants were deeply interested in the lectures.

Lastly, we exhibited samples of larval bluefin tuna and eel, photographs of Itasenpara Bitterling, and posters showing research results. We also exhibited Acheilognathus rhombeus, Rhodeus ocellatus ocellatus, and eel in tanks. Many participants looked at them interestedly before the lectures or during the break. These exhibitions helped the participants to deepen their understanding of our researches and to better communicate with us.