Present State of Bluefin Tuna Aquaculture in Japan

Transcription

1 Present State of Bluefin Tuna Aquaculture in Japan Hidemi KUMAI Fisheries Laboratory of Kinki University Uragami 468-3, Nachikatsuuracho, Wakayama Introduction Five species of Tunas are important among those consumed in Japan. According to the survey of the Asahi Newspaper Publishing Company, among the total catch of Tunas, the catch of Allison's tuna amounts 63.5%, Long-finned tunas amounts to 17.0%, Big eyed tunas 16.1 %, Bluefin tuna only 2.1 % and Southern bluefin tuna 1.3 %. Among them, Bluefin tuna are the largest-sized, and said to have the body length of about 3 m, weighing as much as 500 kg. This kind of tuna is very attractive with a big yearly growth rate, good taste and the highest market prices owing to their scarcity, yielding high economical effect as the culture fish. Bluefin tunas are distributed in the high altitude sea area (about N) of the northern hemisphere in the Pacific and Atlantic Ocean and they are called Temperate Zone Tuna. The Pacific Ocean Bluefin tuna is a subpopulation whose main spawning ground is the East Sea Area of Taiwan, and it has the migration around the Japanese Islands and a part of them has a transoceanic migration far to the West Coast of America. Atlantic Ocean Bluefin tunas are considered to have two subpopulations whose spawning grounds are Mediterranean and the Gulf of Mexico. At the eighth conference of Washington Convention (CITES) Treaty Powers held in Kyoto in March 1992, Sweden proposed that the Atlantic Ocean Bluefin tunas should be registered in the treaty which gcontrols international commercial dealings of wild animals and plants that are threatened to become exterminated h. However, the proposal at that time was withdrawn because there exists a strict fishing control imposed on Atlantic Bluefin tunas by the Intentional Committee for Conserving Atlantic Tunas (ICCAT) in order to use successively the tuna resources effectively. This incident, however, implies the world trend for fishing control to ensure lasting production of tuna resources. Enforcement of the policy for conserving resources is urgently required especially for Pacific tunas which are not included in any international resource control system equivalent to that of ICCAT. Here we discuss the history, the current state and problems of Bluefin tuna aquaculture in Japan until now. History of the aquaculture study Because there are various problems for the culture of fishes which have big bodies and a large migratory area, tunas have been the last fish to be cultured, and the culture of them has been a long dream for those who are engaged in this field. The Fisheries Laboratory of Kinki University was preparing for this study, choosing the coastal area of Kushimoto-cho, the point of Kui Peninsula where many young Bluefin tunas come over in 1970, when the Laboratory happened to be requested by the Fisheries Agency to study gexperiments on the development of tunas culture technique h. Thus the Laboratory started to study the aquaculture of tuna for the first time. The year class which had passed 5 years of culture in 1974 succeeded in natural spawning in a net cage in 1979 for the first time in the world, providing hatched fry fish for the culture. After that in 1980 and 1982 a small number of

2 294 H. Kumai (1997) spawning with the same year class was observed, but after that no spawning was seen. In 1994, however, after 12 years of blank result, a large quantity of spawning was observed with 7 years-old cultured fish, which successively spawned in 1995 providing samples for the culture experiments. About 10,000 individuals of these artificially hatched juveniles were transferred to the floating net cage to be cultured, among which 50 individuals survived growing up to the body weight of 2-3 kg aging just 1 year-old on the end of June, In October, 1995, 87 juveniles in which the average fork length was 19.9 cm (14.2 `23.7 cm) and average weight was g ( g) were released, respectively tagged with a dart type, for the first time in the world as the artificially hatched Bluefin tunas. Further, besides the Kinki University, many groups have started the studies and culture businesses: Japan Sea Farming Association (JASFA) was the first to start in 1985 at Ishigakijima; New-Nippo Corporation in the same year of 1985 at Otsuki-cho, Kochi Pref.; Nippon Formula Feed MFG. Co, LTD from 1986 at Utsumi-mura, Minamiuwa in Ehime Pref.; Maruha Corporation from 1987 at Setouchi-cho in Amamioshima; New-Nippo Corporation again from 1990 at Motobucho in Okinawa mainland; Marino-forum 21 Foundation at Kasasa-cho in Kagoshima Pref. Especially, JASFA started its study with the first trial of creating a large scale culture farm by partitioning off a small bay by a net. Among them, Nippon Formula Feed MFG. Co, LTD and Maruha Corporation succeeded in obtaining fertilized eggs from reared breeding fishes and their respective studies on the culture of juvenile fish and seed production are in progress. New-Nippo Corporation, on the other hand, aiming at the commercialization of culturing Bluefin tunas by raising natural young fish, shipping the products to the Tokyo Central Wholesale Market, thus cultured tunas are now going to be evaluated. Preparation of seeds for culture Seeds of bluefin tunas depend on young fish caught naturally (called as Yokowa), because their artificial production is impossible at present. As mentioned before, the subpopulation migrating to Japan has the main spawning ground in the sea area of east of Taiwan, appearing at the coasts of the Japanese Islands in the period of July -V September with rapidly grown body length of 20 `30 cm. We have tried to catch them by trolling at the littoral around Shionomisaki, Wakayama Pref, from It is necessary to elaborately put the young fish into a fish preserve releasing it from a fish hook immediately after it is caught without touching its body. Tunas in general consume much oxygen, and moreover, are fragile against scraping, so it requires a fairly high technique to put them into a fish preserve successfully after they are caught. The survival rate until the feeding was very low at first with annihilation in not a few cases, but recently with the development of fishing techniques it becomes stable at about the level of 80 %. The places famous for fishing the seed of young bluefin tunas are coasts of south Wakayama Pref., the near seas of Kashiwajima, Kochi Pref., and the near seas of Kasasa-cho, Kagoshima Pref. Most of them have a total length of 20 `30 cm, body weight of g although there are some differences depending on the place and the year class. Also there are yearly differences. Thus, the artificial seed production remains to be an important subject for the stable supply of seed in the future. Facilities and environments of culture The young fish caught are first contained in a fish preserve for the feeding. A small size of the preserve is desirable for the continual observation of conditions of fish, many of them being as small as m ~ 10 ` 12 m ~ 5 `10 m depth. The fish grown up to weigh 3 `5 kg are transferred to a bigger preserve to start the main culture. The fish preserve should be so deiced as to prevent distortion by the tide current, as to have enough space for the habitation and to minimize insertion of fouling organisms. As to the shape of the net preserve, there are round, square and rectangle type, and sizes of the preserve are: round, about m in diameter, 7 ~ 20 m in depth; square, 20 `40 m ~ 20 `40 m ~ 10 `20 m, and rectangle, 20 `40 m ~ 26 ` 60 m ~ 12 `20 m. Materials used for the net are mainly metal wire and

3 Present State of Bluefin Tuna Aquaculture in Japan 295 synthetic fiber. A metal wire net preserve is excellent in being free from distortion, having a good exchange of sea water and effective living space for fish. Nevertheless, owing to its short life of about two years and inconvenience for handling, most of the preserves in these days are made of synthetic fiber. For frame work of the preserve, steel pipes or steel bars are used. The frame work type is durable only in case when it is installed near inland gulf where influences of the wind and waves are small, and at the open sea area where wind and waves are strong, the float is used in stead of the frame. For the both types, sinkers are fixed at the bottom of the preserve net in order to maintain the net gear geometry in normal conditions. When the preserve is contaminated by fouling organisms, cleansing with the cleaner or the exchange of net is required to maintain the smooth exchange of sea water. The temperature of the water suitable for the growth of Bluefin tunas is considered to be 15.0 `28 Ž. Therefore, the sea whose temperature is kept high in this temperature span for a long time of period is use of formula feed is also considered, and some tests have been already started. Further, such studies on nutrition requirements, etc., are needed for its full scale applications. When the formula feed for tunas is developed in the near future, it will contribute to the progress of culture of tunas, providing conveniences for improving flesh qualities, for adding substances to promote the maturity for reproduction, and also for dosing in case of an outbreak of diseases. The growth rate differs greatly depending on environmental temperatures of culture ground, for example: at the culture farm of JASFA in Amamioshima where the climate is mild and warm, 3 years-old fish are observed to weigh as much as 97.0 kg and kg in May 1996, most of them being estimated to have grown up to weigh 90 ` 100 kg. At Kushimoto culture farm of Kinki University in the north, on the other hand, results are such that even the biggest on barely reaches up to 50 kg of weight. Here the results at the culture farm of Kinki University at Kushimoto Oshima desirable for the culture site. Besides, inland gulfs where there is a great amount of water inflow in case are shown. According to these results, the fish weighing 0.1 ` of a big rainfall are not suitable, because muddy water exerts a serious influence upon bluefin tunas. The sea area where a lot of ocean water flows in from the open sea, providing rich dissolved oxygen and high and stable salinity is desirable for the fish preserve. Feed and growth Sardine, sandeels, sauries, chub mackerel, Japanese horse mackerel, scads, and cuttlefishes have been employed in raw or chilled products for the feed of bluefin tunas. Although they prefer sardines and sand eels are the most suitable feed to provide the proper size of fish which fits a mouth caliber of bluefin tunas which grow very fast. Chub mackerels are convenient because they can be caught in various sizes in accordance with the fishing seasons and because they can be stocked in freezers for use at any required moment. Thus, as the feed, chub mackerels are mostly used, occupying a little more than 70 % of the amount used, and sardine sauries, saurels and sandeels follow in the order. The 0.5 kg at the beginning when it is initially caught grows up to 3 ` 8 kg after 1 year; 10 `30 kg after 2 years; after 3 years, weighing in the average 18 kg, the largest 50 kg; after 4 years, the average 25 kg, the largest 60 kg; after 5 years, average 40 kg, the largest 90 kg; after 6 years, the average 55 kg, the largest 120 kg and after 7 years, the average 80 kg, the largest 140 kg. Apart from this, two of the year class fish in which the started in 1974 have been reared for 22 years and they are estimated to weigh more than 200 kg now. This size, however, is not the largest of this year class; the largest fish of the mixture of 1978 and '79 year class, reared for years, had the body weight of kg, total lenght of cm, fork length of cm, body height of 71.0 cm and body width of 44.5 cm. Conversion factors of Bluefin tunas remain a matter of estimation with dead fish and a few samples because the measurement of living fish can not be used. The results estimated by Kinki University on 1990-year class were: for 0 `1 year-old fish, 6.8 ` 7.1; for 2 years-old fish, 6.9 `10, and for 3 `4 years-old fish.

4 296 H. Kumai 0997) Daily feeding rates, which differ with water temperatures are: for 0 `1 year-old fish, 5.6 `2.6 %; for 2 years-old fish, 3.8 `1.4 %, and for 3 `4 yearsold fish 2.2 `1.3 %. Thus, such tendencies of increase %, and further, matured transparent eggs were calculated as about 4.4 hundred thousand. From these findings, it was estimated that the number of spawned eggs from a fish at one time was about 4.4 hundred in conversion factors and decrease in daily feeding thousand grains. rates in accordance with the aging were similarly observed also in bluefin tunas as in the case of other fish groups. Maturation and spawning It was confirmed that fish group which was cultured for 5 years and which had the total length of 130 `180 cm, body weight of 50 `90 kg (estimated number of 57 in total, consisted of male and female) naturally spawned for the first time on 20th of June, 1979 in the net cage (30 m in diameter and 7 m in depth). In that year, about 1.6 million grains of fertilized eggs were obtained. The surface water temperature was 21.8 ` 25.6 Ž. That year class spawned also in July, 1980, and further, they spawned in July, 1982, but that was the last spawning, thus the spawning was not confirmed afterwards. That year class was consisted of 200 fishes being estimated to weigh 45 `140 kg, about 80 kg in the average. It began spawning on 3rd of July, and successively spawned during 41 days excluding the period of typhoon, and about 84 million grains of fertilized eggs were collected. It had good results that the average egg diameter of } mm and oil-globule of } mm, and that the hatched rates were 86.6 `100 %, most of them being more than 90 %. In case the range of surface water temperature was 23.2 `29.2 Ž, and that of the density of sea water was `24.80 (ƒð15), spawning time was focused to 17:30 `18:00 o'clock. Further, during the maximum spawning time of spawning group, the fishing of matured male and female individuals was carried out between 14 `15 o'clock just before the spawning, and the survey of gonad was made. As the results, the largest GSI of female was 4.3 %, and transparent eggs were partly recognized, and that of the male was 3.3 % and the sperms were released. From the egg diameter composition, it was concluded that Bluefin tunas had multiple spawnings. The fecundity was about 7.8 million, and egg group in which egg diameter was in the range of 0.8 `1.0 mm occupied 25.1 Culture of hatched larva and juvenile-to seed production As the result that the fertilized eggs that were naturally spawned for the first time in the net cage were hatched and reared, they survived until 47th day after hatching, and the last one grew to the body weight of 2.3 g, the total length of 59.4 mm and the body height of 13.2 mm. Further, in July `August, 1996, the fertilized eggs that were naturally spawned from reared 7 years-old fishes were accommodated into a breeding tank indoor and they were artificially hatched, and the culture of juvenile fish was made under the condition of water temperature of 25.0 ` 28.0 Ž. The total length of hatched larva was 3.18 } 0.18 mm and they began to take feed from the 2nd day after hatching, and they grew to have the length of 6.5 }0.5 mm at 10th day and 13.7 }5.4 mm at 20th day. The growth from the juvenile fish period was remarkable, thus the total length of hatched larva became 34.9 } 9.5 mm on 30th day, and they grew to the length of 56.7 }13.6 mm and the body weight of 2.2 }1.7g at 30th day, and to the length of }25.4 mm and the body weight of 24.1 } 17.0 g at 50th day respectively. As to the feed, rotifer was given from the 2nd day after hatching, Arternia was given from about 10th day, and hatched larva of such fishes as red sea bream and Japanese parrot fish was given, as well as formula feed from 17 `20th day, and minced meat of small fish such as sardine and sand eel from 24 `33th day were given, respectively. What was transferred earlier to the floating net cage to be cultured was done on 27th day after hatching. Afterwards, at the 182nd day after hatching, the total length of 40.7 cm and the body weight of 1,168.2 g were attained for what had the rapid growth, but finally the last one fell dead at the 246th day after hatching. At that time, the total length was 42.8 cm, the body weight was 1, g, the body height was 11.2 cm and body width was 6.9 cm. In the

5 Present State of Bluefin Tuna Aquaculture in Japan 297 rearing of juvenile fish of bluefin tunas, it is said as the problem that the early reduction is great, an the survival rate is 40 `10 % at 10th day, 12 `2 % at 17th day, and 1.2 `0.1 % at 30th day after hatching. Especially as to the reduction at nearly 20th day after hatching, it is owing to the strong internecine specific to this species, and further, the death by punching to the tank wall and net wall become a great cause of these reduction. Therefore, for the mass-production of the seed of bluefin tunas, the preventive measures against these causes are the largest problem at present. Further, in 1995, the same age class as in 1994 (8 years-old fish) began spawning on 23rd of June, and as the results of the similar culture as that of the previous year, about 10 thousand fish were transferred to the floating net cage to be cultured. As above mentioned, about 50 young fishes that have grown to the body weight of 2.0 `3.0 kg (estimation) on the last day of July still survive now. If the method of surely obtaining the fertilized eggs from reared breeding fish, as well as the technology for efficiently performing the culture of hatched fry and for enhancing the survival rate as in such a case of red sea bream and Japanese flounder are established, the realization of culture of bluefin tunas by the artificial seed may be possible in the near future. References 1) Tokyo University of Fisheries Editorial Committee of Extension Lecture. (1985) : Tunas-from production to consumption pp., Seizando, Tokyo. 2) Kumai, H., O. Murata, S. Okamoto, Y. Mukai, M. Nakatani, S. Miyashita, and T. Harada (1995) : Growth and spawning of bluefin tuna at the coastal area of Kushimoto and Oshima. Proceedings of the 1995 spring meeting of the Japanese Society of Fisheries Science. 3) Murata, O., Y. Ishitani, S. Miyashita, M. Seoka, Y. Kubo, and H. Kumai (1995): Condition of the reared bluefin tuna gonad in the spawning season. Proceedings of the 1995 spring meeting of the Japanese Society of Fisheries Science. 4) Sawada, Y., T. Okada, O. Murata, S. Miyashita, and H. Kumai (1995) : Relative growth of artificially hatched bluefin tuna at the early developmental stage. Proceedings of the 1995 spring meeting of the Japanese. Society of Fisheries Science. 5) Miyashita,S., O.Murata, M.Nakamura, T.Yokoyama, H. Yoneshima, S. Oda, T. Okada, T. Nasu, N. Takahashi, and H. Kumai (1995): Future aspect of the seedstock production of bluefin tuna. Proceedings of the 1995 spring meeting of the Japanese Society of Fisheries Science. 6) Kumai, H. (1995) : History and present state of bluefin tuna aquaculture. Saibai, No. 76, ) Miyashita, S., Y. Sawada, H. Nakatsukasa, H. Yagi, S. Oda, O. Murata, and H. Kumai (1996) : Relative growth of artificially hatched bluefin tuna at juvenile and young stage. Proceedings of the 1996 spring meeting of the Japanese Society of Fisheries Science. 8) Koiso, M., S. Masuma, K. Teruya, S. Tanaka, O. Murata, S. Miyashita, S. Oda, and H. Kumai (1996) : Handling and tagging of artificially hatched bluefin tuna. Proceedings of the 1996 spring meeting of the Japanese Society of Fisheries Science. 9) Nakatsukasa, H., S. Miyashita, O. Murata, K. Kato, S. Masuma, M. Koiso, K. Teruya, and H. Kumai (1996) : Anesthetizing of artificially hatched bluefin tuna. Proceedings of the 1996 spring meeting of the Japanese Society of Fisheries Science.