|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 Environmental Conservation and Source Dynamism Group
Wataru Sakamoto (Environmental Conservation and Source Dynamism Group, Fisheries Laboratory)
Our Group was organized to research changes in the environment of culture fisheries and their impact on cultured fish. The Group researchers are COE members affiliated with the Graduate School of Agriculture and the Fisheries Laboratory. These members are specialists of one of the three fields, that is, biological oceanography and microbial ecology, biotelemetry, and the study of fishing gear and fish behavior based on fluid dynamics. Research themes were established separately while strong interdisciplinary coordination was maintained. Presented below are the achievements made in 2005 academic year.
[ Culture environment ]
We are devoted to the following four research themes. (1) Evaluation of self-purification in bay fishery waters: In order to perform sustainable fish culture, it is necessary to make an accurate evaluation of self-purification in waters, that is, the ability of microbial communities to decompose and mineralize. Previous studies have shown that decomposition and mineralization in waters are most active in winter and that the purifying ability is stronger in the tuna culture preserve waters in Oshima than in the Tanabe Bay, where culture has been done for many years. (2) Improvement of the breeding water environment for seedling production: Production of seedling for culture involves the problem of mass mortality in seedling that takes place early in the breeding process. There are many factors behind mass mortality, including bacterial communities in breeding water. Studies conducted so far have revealed that seedling growth and survival are lower when specific bacterial communities are predominant in breeding water. We are now focusing on the relationship of phytoplankton added to the breeding water and bacterial communities, assuming that if we can use phytoplankton to control bacterial communities in breeding water, we would be able to control breeding water in a safe, drug-free way. (3) Hygiene control for culture environment and use of electrolyzed sea water: We are evaluating the effectiveness and safety of electrolyzation, a cheap and easy-to-spread technology with good sterilizing power. So far, we have verified the safety of electrolyzed sea water in mutagenicity tests etc. We have also confirmed that this technology is effective for the sterilization of sea water and rotifer used as living feed. Electrolyzed sea water can not only be used for the sterilization of breeding water and living feed, but also can be applied to the treatment of culture wastewater, so we think that it is helpful in the conservation of the quality of surrounding waters. (4) Elucidation of the environment of infection by pathogenic microbes: The environment of infection cannot be eliminated unless we know where in natural waters microbes causing diseases in fish exist and how much. We are now working on white spot disease in marine fish (red sea bream) and coldwater disease in freshwater fish (sweetfish). In the case of coldwater disease, we have found that the responsible bacteria exist in the various environmental samples taken from the river surveyed, from upstream to downstream. We also have found that the coldwater bacteria found in these samples include the types which infect completely different kinds of fish, so we are developing a high-sensitivity detection method for finding only the coldwater disease bacteria which inflict damage specifically on sweetfish. White spot disease used to break out in closed environments such as aquariums and on-land culture ponds, but recently it has been reported from coastal culture preserves etc. In order to elucidate the environment of white spot disease bacteria infection, we are working on the development of a high-sensitivity detection system for white spot disease bacteria in floating mud on the bottom of the sea, where its cyst is said to exist.
[ Biotelemetry ]
Themes in this field are as follows. (1) The elucidation of the impact of changes in the above-mentioned environment upon the feeding and digestion, growth and maturity, and behavior of fish in culture preserves: Basically, we implant in the abdominal cavity of bluefin tuna a small recording device which can measure temperature, depth, and biaxial acceleration at the time of swimming and a transmitter which converts the body temperature, the heart rate, and other internal information into ultrasonic for remittance, taking measurements for more than one year at the longest, including those of environmental changes. The body temperature of bluefin tuna is kept higher than water temperature, so we can understand the processes from feeding to digestion from temperature changes. On the basis of these, we have understood changes in the amount of feeding which occur as water temperature changes and the different amounts of time required to digest different kinds of feeds. In particular, we analyzed the differences between squid and mackerel in terms of feeding and digestion, and the impact that changes in water temperature during the year have upon the body temperature. (2) Analysis of the regression process after release of larval bluefin tuna obtained through seedling production: We measured the swimming behavior of bluefin tuna around Payao, where they stay for a long time, making a comparison with the behavior of those cultivated in preserves. We also tracked and analyzed the behavior of those which were contained in a preserve at the larval stage and were released 80 days later, finding that on the first day of release, they swam at the same depths and speeds as in the preserve, but on the second day they began to swim faster at greater depths, adapting to the marine environment. It seems that even fish contained in a preserve at the larval stage regress within a few days after they are retuned to the sea. (3) Experiment for comparing the swimming behavior of bluefin tuna in large and small preserves under a cross-group project: We have identified significant differences between the two preserves, finding that the fish in the small preserve have to constantly change their posture while swimming to avoid colliding against the net, feeling additional stress. This test result seems to affect flesh quality and growth, providing useful information that we can refer to when we design optimum culture preserves.
[ Numeric fluid dynamics design of optimum culture preserves and fish dynamics analysis ]
There are two major themes in this field. (1) Analysis of hydrodynamic load on swimming bluefin tuna and the swimming energy cost: The estimation of energy required by fish in preserves is necessary for determining feeding efficiency, growth and the amount of feeding, the size of a preserve, and the swimming ability. We have analyzed the relationship between the body movement of swimming fish and the energy of movement through numerical fluid analysis and high-speed image analysis. It was assumed that bluefin tuna needs a lot of energy as it swims very fast, but the analyses have shown that required energy is only slightly larger when it swims at a high speed than when it uses inertia without moving the body. This is the world's first discovery. (2) Relationship between bluefin tuna's school behavioral characteristics and visual characteristics that improve as it grows: The school behavior of swimming at the same speed and interval is one of the characteristics of the swimming behavior of mature bluefin tuna. However, the optic nervous system is not fully developed yet at the larval stage, so larvae often collide against the wall of a culture preserve or go into panic at a sudden change in illumination, resulting in mass mortality. This theme is taken up as a fundamental experiment to prevent the occurrence of these phenomena. We have found so far that bluefin tuna's visual characteristics improve as it grows and its ability to distinguish matter in dim light is greater at higher stages of growth. We have also found that since bluefin tuna move on to the school behavior of swimming at the same speed and interval as they grow, orderly school behavior can also be observed at a low illumination side as they grow in size.
[ Future activity ]
We will study the management of water quality in culture fisheries, the heath control of cultured fish, the relationship between the size of a preserve and the number of fish contained therein, and the impact of environmental changes upon the survival, growth, and maturity of cultured fish, combining the achievements in the fields of environment, biotelemetry, and fluid dynamics.
Status of the cross-group project
Shigeru Miyashita (Cross-project member, Fisheries Laboratory)
At this research site, we aims to ensure systematic coordination between the research groups and contribute directly to the development of the culture industry. As reported in Volumes 3 and 6 of this News Letter, we launched two projects 'Research on the development of a bluefin tuna culture manual' and 'Research on the development of environmentally friendly seedling production technology' in 2004. Last year, we started 'Research on the aptitude of crossbred red sea bream (female) — black sea bream (male) for cultivation in South Korea' in accordance with the academic agreement with and at the strong request of Chonnam National University in South Korea. Presented below is the current status of these projects.
(1) Research on the development of a bluefin tuna culture manual
The experiment in the first year was suspended as the test site was devastatingly damaged by typhoon No. 18 which hit the Amami region two months after the start of the experiment, and was resumed in June 2005. The objective was to investigate the impact of the preserve size using one 30m-diameter preserve and two 16m-diameter preserves and to study the impact of differences in the feeding rate in the two small preserves. This breeding experiment appeared to have started smoothly without being affected by typhoons, but we met with a series of thunders from July to August, soon after the start of the experiment, and with many collision deaths possibly attributable to these thunders, seeing a sharp decline in the survival rate, especially in the small preserves, to 43% (24 survivors) and 25% (13 survivors), respectively, as of the end of August. Our pessimistic predictions proved right when we took samples at the end of May this year, finding no difference between the three preserves in terms of culture results, including feed efficiency, the degree of obesity, and the average weight, which was around 35kg for all the preserves. These results contributed to the analysis of swimming behavior by the Source Dynamism Group, but were not useful for the three other groups.
In 2006, we planned an experiment to investigate the impact of density. But since the start of the experiment was delayed until July, we had to treat (one-year-old) test fish having a weight of approximately 15kg at a high water temperature of 29 degrees centigrade, and we met with the death of more than 20% of the test fish between fishing and containment and had to suspend the experiment. Thus, the series of experimental failures have reminded us how difficult it is to conduct experiments with cultured bluefin tuna, especially those aged one year or above. We now have to consider a limited experiment plan because of the starting time and the fish size.
(2) Research on the development of environmentally friendly seedling production technology
This research is designed to develop environmentally-friendly, drug-free production technology, focusing on microbes, while aiming at the development of seedling production technology for the fish species (small-larva types) which are so small at the larval stage that it is difficult to feed rotifer. In other words, its objective is to develop new initial feeds and breeding water control technology from a microbial approach, shedding the traditional concept. As was reported in Volume 6 of this News Letter, last year we conducted research on the feeding ecological characteristics of grey large-eye bream and blubberlip snapper in Malaysia, among such species, and fundamental research on the relationship between microbial communities in breeding water and mortality in larvae, using red sea bream, bluefin tuna, and other model fish species. This year, we first conducted a feeding experiment using plankton communities, larval bivalves, etc., in natural sea water as feeds with a view to understanding the ecological characteristics of larval grey large-eye bream and blubberlip snapper at the start of feeding, and then conducted an experiment to attempt the breeding of such fish species on new feeds and investigate the growth and survival of the larvae immediately after hatching, the microbial community structure, changes in water quality over time, etc., in order to elucidate the optimum biological, chemical, and physical breeding environment for larvae. Now that grey large-eye bream have finished spawning, Yoshizumi Nakagawa, Doctorate Researcher, will conduct a grey large-eye bream (locally called hoi-tai-kai) breeding experiment for about one month from September 29 at the University Malaysia Sabah Borneo Marine Research Institute, with which Kinki University concluded an academic exchange agreement.
(3) Research on the aptitude of crossbred red sea bream (female) - black sea bream (male) for cultivation in South Korea
Recently, the seawater fish culture industry in South Korea has suffered devastating damage including mass mortality in red sea bream due to an unusually low water temperature in winter, threatening to decline. To overcome this situation, we received a request from Chonnam National University, with which we concluded an academic exchange agreement, for joint research on the aptitude of these crossbred fishes developed by us, for cultivation in South Korea, and included this among our cross-group projects. This species does not have a reproductive function and does not grow as much as red sea bream, but is highly resistant against low water temperature, low specific gravity of sea water, and low dissolved oxygen and is thus expected to have great potential for contributing to the promotion of the South Korean culture industry as a new fish for culture. The purpose of this research is to conduct culture and sales experiments for this species in Chungmu and Yeosu, two major culture sites in South Korea and verify the ripple effect of transfer. We will start the experiments by transporting approximately 20,000 larvae in live fish cars at the end of September this year.
Report on Science Cafe @ Kindai COE 1st Session — Life of Ever-swimming Tuna —
At Ashibi-no-sato in Nara Town on July 22, 2006
Erina Nagata, COE Doctoral Researcher (Environmental Conservation and Source Dynamism Group, Graduate School of Agriculture)
Science Cafe opened on a sunny day after the rain lasted for days. Ashibi-no-sato is a pickles shop in Nara Town, to which a relaxing restaurant is annexed. When we opened the reception desk at 14:30, we received a wave of customers. Most of them submitted applications in advance by email or telephone, while five of them came without prior application. At 15:00, Nagata gave a brief explanation of the Kinki University 21st Century COE Program and Science Cafe, which opened immediately thereafter. This session consisted of Part 1 on the provision of topics, Part 2 on discussion at each table, and Part 3 on discussion by all the participants. The topics were given by five members of the Source Dynamism Group and were intended to constitute a single story. All the participants listened silently to the lecturers, looking carefully at the slides. Some even took memos.
There was a ten-minute break after the provisions of the topics. At least one of the PDs, DCs, MCs, etc., of the Source Dynamism Group attended each table as a supporter, starting brisk discussions at each table over tea. When the topics were offered, all the participants were silent and we were afraid that there might not be brisk conversations, but our pessimistic predictions proved wrong when we saw the participants discussing in a congenial atmosphere, smiling. We heard 'Really!' here and there. We felt the second rest time came very quickly. When we announced the beginning of the break, the discussions at the tables did not stop and no one left for the restroom.
At the Q&A session, the questions asked at the tables were advanced by the supporters to and asked by the persons who provided the relevant topics. Due to the limited time, the number of questions that can be answered by the lecturers was limited. It seemed that many questions were raised at each table, so we are sure that the supporters had difficulty in choosing the questions to advance. Lastly, some questions which impressed the lecturers are shown below.
- Is tuna swimming all the time without sleeping?
- How good is the fuel efficiency for swimming tuna?
- Is it possible that tuna joins a school of another fish?
- Does the leader of the school change?
- Doesn't tuna have a cramp, swimming all the time?
- If tuna has a cramp, would it die as it cannot breathe?
- Does tuna have a better eyesight than a shortsighted person?
Science Cafe closed successfully after 17:00. Many of the participants' comments given in the questionnaire sheets collected after the closure were like 'I will definitely come again' or 'It was very interesting', and all the staff felt relieved. Please visit the website of Science Cafe @ Kindai COE for further details of the first session and the results of the responses to the questionnaire, and what happened later to Science Cafe.
URL : http://sciencecafe.yamanoha.com/