INTRODUCTION
The concept of rearing fishes in floating net cages in sheltered bays or in fish ponds supplied with seawater has been applied in Japan to several coastal species of high value, and commercial ventures are well established. In 1967 the production of cultivated marine fishes in Japan amounted to 27,103 tons in gross weight worth over $24 million and consisted of 98.6% yellowtails, 0.25% puffers or globefish, and 1.2% other marine fishes (Harada, 1970). Production of yellowtail has increased remarkably in recent years, as shown by the following table:
| Year | Tons |
| 1961 | 2,579 |
| 1962 | 4,758 |
| 1963 | 5,083 |
| 1964 | 9,493 |
| 1965 | 18,083 |
| 1966 | 19,629 |
| 1967 | 26,712 |
| 1968 | 30,774 |
Production of puffers or globefish by aquaculture has decreased year by year because of the shortage of seed fish, and by 1968 was only 43 tons (Furukawa, 1970).
A number of species of marine or anadromous fish are being cultivated in seawater in Japan on an experimental or commercial basis, as listed in the following table:
Species of fish cultivated in seawater in Japan
| Seriola quinqueradiara | yellowtail |
| Seriola purpurescens | amberjack |
| Longirostrum delicatissimus | striped jack |
| Fugu rubripes rubripes | puffer (globefish) |
| Chrysophrys (Pagrus) major | red sea bream (red porgy) |
| Acanthopagrus schleglii1 | black sea bream (black porgy) |
| Sparus sarba | silver sea bream |
| O plegnathus fasciatus | Japanese parrotfish |
| Oplegnathus punctatus | spotted parrotfish |
| Paralichthys olivaceus | bastard halibut |
| Sebasticus marmoratus | scorpionfish |
| Oncorhynchus keta | chum salmon |
| Salmo gairdneri irrideus | rainbow trout |
| Salvelinus pluvius | steelhead |
The short time available for the present survey in Japan prevented a complete survey of the status of aquaculture of each of the species listed above, and the following summary is based on brief visits to select locations and several published articles listed below.
Culture of the yellowtail, Seriola quinqueradiata, is the most successful marine fish farming venture in Japan, and production from farming now exceeds landings from fishing of wild stocks. Yellowtail culture is conducted by individuals, companies, or fishermen's associations in floating net cages and in fish ponds which are made by partitioning sheltered places from the sea with nets or earthen dams. The great expansion during recent years is because of the increase in the number of floating net cages, since the number of locations suitable for ponds is limited.
Although spawning, fertilization, hatching, and raising to seedling size have been achieved experimentally for yellowtail, methods have not been developed to the stage that seedlings can be produced in commercial quantities for the industry (Harada, 1970). Instead, young fish 5-15 cm in length are caught 5-15 miles offshore during April and May. Young yellowtail collect under floating patches of seaweed, and the fishermen simply encircle a mass of seaweed and catch the small fish which are placed in small floating net enclosures. To conserve the natural resources, the Japanese Government has limited the number of young yellowtail which may be supplied to all farms in the country from 28,363,000 to 30,780,000 per year (Harada, 1970).
The young yellowtail are reared in small net enclosures for 1-2 mo until they reach a length of 25-40 mm. These seedlings are then placed in larger floating net cages approximately 6 x 6 x 2 m in which 1,500-2,500 fish can be kept. By December the yellowtail reach a size of 1.0-1.5 kg and are shipped to market.
In southern Japan where the minimum temperature exceeds 11°C, it is possible to hold yellowtail through the winter and sell them in April when they reach a weight of 2-3 kg, but winter temperatures farther north are too low for yellowtail. According to Fujiya (1969), about 95% of the yellowtail are shipped to market by December. Detailed descriptions of yellowtail farming procedures are included in papers by Harada (1970), Furukawa (1970), and Fujiya (1969).
Problems of the industry include 1) a stable supply of seedlings, 2) disease control, and 3) adequate food supply or development of suitable artificial diets.
1)Stable supply of seedlings. Production from yellowtail farming is limited to approximately the present level because of government restriction on the number of young fish which can be taken from coastal waters. According to Harada (1965), it is highly desirable to produce seedling yellowtail by artificial fertilization in a hatchery. This has been accomplished recently on an experimental basis, but has not been perfected for commercial application. In the meantime, Harada recommends collecting the seed (larval or juvenile fish) at as early a stage as possible and keeping them under careful management to reduce mortalities.
Although production could be increased by improving growth rate, reducing mortality, or by extending the rearing time in places where winter water temperatures are not too low, ultimate development of the industry will require maintenance of a spawning stock, collection and hatching of eggs, and rearing of larval stages to assure a dependable supply of seedlings.
2) Disease control. The monogenetic trematode, Benedenia seriolae, infects the skin of the yellowtail causing an unsightly appearance, loss of appetite, weakening or death of the fish. This parasite is considerably less resistant to low specific gravity than the host fish and consequently is easily controlled by dipping the infected fish in fresh water for a few minutes and then returning it to seawater. The time of dipping must be shorter in the summer (3 min at 26°C) than in the autumn (5 min at 16°C) to prevent damage to the fish. Since this parasite grows very fast and becomes adult within 2 or 3 wk. the freshwater treatment must be repeated frequently during periods of infection.
Another monogenetic trematode, Axine (Heteraxine) heterocerca, infects the gills of yellowtail causing anemia which may kill the fish. Treatments, according to Fujiya (1969), include 4-min bath in water containing 4% salt, 2) dipping in a I % solution of "Tremaclean" for 30 see, and 3) oral treatment by including "Bitin" (4,5-dichlorophenol) in the food.
The bacteria Vibrio can cause extensive infections in yellowtail populations. Treatments include incorporation of sulfa drugs or antibiotics in the food.
Virus diseases are suspected, but no information is available concerning these.
The feeding of oxidized, unsaturated fatty acids contained in fish used as food causes nutritional diseases of yellowtail. This can be prevented by feeding white-meated fish instead of anchovy, mackerel, and sand lance.
3)Adequate food supply or development of artificial diet. Farming of yellowtail in Japan depends on availability of large quantities of cheap fish suitable for use as food. These include mackerel, horse mackerel, anchovy, sand lance, and saury. With conversion rates of 6:1 to 8:1 the food must be obtained at very low price in order to make yellowtail farming economical. Expansion of the industry or perhaps even continuation at the present level will require development of artificial diets which will provide better nutrition for the fish and reduce dietary disease problems. Furthermore, the artificial diet must be available at a price which will permit economic fish farming.
Puffers, also known as globefish or blow fish of the genus Fugu, are in high demand as a luxury food in Japan even though certain species are extremely toxic. About 10 species of edible puffers occur in Japan, but one species, Fugu rubripes rubripes, is used principally for farming ventures. The toxicity of puffers changes seasonally, becoming the greatest in the spawning season from May through June. The toxic substance "Tetradotoxin" occurs mostly in the ovary, liver, intestines and skin, and rarely in the muscle. When prepared carefully by licensed cooks in Japan, puffers are completely safe to eat.
Production of puffers in fish farms has decreased during recent years because of a shortage of seedlings, as indicated in the following table:
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The farming of puffers is generally carried out in the warmer part of Japan since the puffers require water temperatures between 10° and 29°C.Of the 14 management units in Japan, 8 are located in the Seto Inland Sea, 4 in the west Japan Sea area, 1 in the east China Sea, and 1 in the north Japan Sea area.
Traditionally, puffer farming depended on the capture of partially grown fish in the spring, rearing these fish to market size in net enclosures, and marketing them in the winter when demand and price were high. Larger fish, 40-60 cm in length, weighing 1.5 to 2.5 kg, can be fed in enclosures from spring to early winter and then shipped to market. Younger fish, about 200 g when captured, require another year before reaching market size.
Methods for artificial propagation of puffers were developed in Japan in 1960 and are now used commercially. Seedling fish of about 3 g are transferred from the hatchery to the growing net cages in July and should average 550 g by August of the following year. At the end of 11/2 yr, the puffers should reach 800 g, the minimum market size, and after one additional year should weigh 1.5-2.0 kg.
The procedures for rearing puffers are similar to those used in the culture of yellowtail. Since both of these fish are carnivorous, fresh or frozen fish, such as horsemackerel, mackerel, anchovy, sand eel, and saury are used for food. Minced flesh is recommended for fish less than 100 mm in length, but larger fish can be fed chopped flesh.
The fish are fed 4 times a day during midsummer, 3 times a day from September to November, and less frequently during the winter and early spring. Puffers stop feeding in winter when the water temperature falls below 14°C, and this causes a weight loss of about 10% during the winter.
Expansion of puffer farming will require greater production of seedlings through artificial propagation. Detailed description of procedures used in the farming of puffers is given by Fujiya in his 1969 paper, Farming Fisheries in Japan."
The Japanese black porgy, or sea bream, Mylio macrocephalus (also listed as Acanthopagrus schlegelii), is a nonmigratory species found in shallow water along the coasts of Japan, Korea, Taiwan, and China. The annual catch of this species in Japan is 3,600-3,900 tons, about 65% of which is landed in the Seto Inland Sea (Fujiya, 1969). Black porgy can be raised in floating net cages or seawater ponds; and, since this species is more resistant to lower temperatures than some other species which are used in aquaculture, the geographical range suitable for farming is greater. Black porgy are reported to stop feeding at water temperatures below 10°C but can survive temperatures several degrees colder.
The species is omnivorous, feeding on mollusks, crabs, polychaete worms, and seaweeds, so a variety of waste fishes and unutilized mollusks can be used as food. With the conversion rate of 3 or 4:1 in experimental scale farming reported by Fujiya (1969) for fresh fish diets, commercial culture should be economical. Market size fish reportedly can be produced within 16 to 20 mo.
Black porgy farming using "natural seedlings" is of two types, depending on the size fish which can be obtained. Small seedlings, 1 to 4 cm in length, are caught along the coast by seines from late May to late July. These small fish are put in fine-mesh floating cages for 1-2 mo and then transferred into larger mesh net cages. Market size fish, about 150 g, can be expected within 15-18 mo.
The second type of farming depends on capture of seedlings, 10-15 cm in length (30-50 g in weight), in set nets or by angling from May to July. Fish of this size will reach market size after about 6 mo of feeding in floating net cages.
The limiting factor in farming of black porgy is the supply of seedlings from natural reproduction.
Methods for artificial propagation of black porgy have been developed in Japan and with a suitable increase in production of seedlings, porgy farming can be greatly expanded. Further details concerning the farming of black porgy are given by Fujiya (1969).
The red porgy or sea bream, Chrysophrys (Pugrus) major, known in Japan as the "tai" or "madai" is in great demand since it is the traditional fish served at celebrations. The commercial catch of sea breams in Japan was nearly constant from 1965 to 1967, but during 1968 and 1969 decreased slightly to a level of about 30,000 tons (Japan Fisheries Association, 1971).
Research on the farming and artificial propagation of red porgy began in Japan over 70 yr ago but was generally unsuccessful until recent years. In 1958 research on artificial propagation was intensified with more modern facilities are equipment and successful results were obtained on an experimental scale in 1962. By 1965 an experiment in the propagation of red porgy using artificially produced seedlings succeeded at the Propagation Center in the Seto Inland Sea. It now appears that a basis has been established for expansion of red porgy farming, but this knowledge has not yet been commercially applied (Fujiya, 1969).
The Association of Marine Stock Farm of the Seto Inland Sea was incorporated in 1963 to increase the fisheries resources of the Inland Sea of Japan by releasing young marine fishes. In l958, this Association produced 166,686 red porgy in a hatchery and released them into the Inland Sea. The effectiveness of these plantings in supplementing natural stocks is now being investigated. The success of this hatchery also portends the expansion of commercial farming of the red porgy.
According to Fujiya (1969), larvae of the red porgy, 2 to 3 cm in length, are usable as seedlings. They have been grown successfully in floating net cages using fresh fish meat or pellets as food and reach market size in 12 to 18 mo.
Several other species of marine fishes are being cultured in Japan on an experimental or limited commercial basis. These include amberjack, Seriola purpurescens, and the striped jack, Longirostrum delicatissimus. Both of these species can be cultured by using the methods which are so successful with the yellowtail. Teruo Harada of Kinki University is conducting large-scale experiments in the culture of these species at the University facility at Shirahama in Wakayama Prefecture. Commercial culture of these species is especially attractive because there is a demand at prices considerably higher than those for yellowtail.
At the same research facility Harada is studying the artificial culture of many other species of fish including the Japanese parrotfish, Oplegnathus fasciatus, and the spotted parrotfish, O. punctatus, and the flatfish, Paralichthys olivaceus. Paralichthys is in high demand at a price 4 times as great as for yellowtail, so artificial propagation of this species should be profitable. Harada et al. (1966) described growth and rearing methods for the fry of the flounder, Paralichthys olivaceus, obtained by artificial fertilization.
The silver sea bream, Sparus sarba, is also being studied at the Shirahama field station of Kinki University.
Another marine fish Sebasticus marmoratus, known as the scorpionfish is artificially produced in the hatchery of the Association of Marine Stock Farm of the Seto Inland Sea, and 125,536 juveniles were released into the Inland Sea in 1968. Similar releases of sea breams are being made by the Nansei Regional Fisheries Laboratory, many of which are tagged to evaluate the success of these plantings.
Trout have been raised in Japan in fresh water for domestic and export markets for many years and standard rearing methods have been developed.
Recently, methods have been developed for culture of rainbow trout, Salmo gairdneri irrideus, in the marine environment. Three Fishermen's Cooperative Associations in Japan are now rearing trout commercially in the protected waters of coastal bays and estuaries; the most recent a new venture at Ogatsu Bay in Miyagi Prefecture.
Procedures for marine culture of rainbow trout described by Akimitsu Koganezawa, Chief of Shellfish and Fish Research for the Miyagi Prefectural Station, are as follows:
Rainbow trout spawn in December in this part of Japan and are raised in fresh water until the following September or October. At that time they are acclimated to salt water over a period of 12-20 days by gradually increasing the salinity to that of the marine environment which is about 34°/oo. Koganezawa has determined that mortality during acclimation can be minimized by increasing the salinity 10% each day except at the levels of 40% and 80% of the salinity of seawater which appear to be more critical. The fish are therefore held at least one extra day at these salinities.
At the time of transfer to the sea the trout weigh 100-l50 g and are about 18-23 cm in length. The trout are harvested the following August at 1.5-2.0 kg, but some may reach a size of 3.4 kg.
Maximum survival during the marine phase of this aquaculture system is 90%; minimum survival is 60%; mean survival is about 70%. Bacteria of the genus Vibrio are the major cause of mortality, but infections can be controlled to a certain extent by the use of nitrofuran, sulfa drugs, and terramycin. In the United States, nitrofuran probably could not be used for this purpose since it has not been cleared for use in treating food products by the Food and Drug Administration.
A new commercial trout farming project was observed at Karakuwa at the head of Ogatsu Bay during October 1971. This project, which is operated by Fishermen's Cooperative Association with the guidance of Koganezawa, included shore-based facilities for rearing trout and acclimating them to seawater and a series of net enclosures for culture of the trout in the marine environment.
Shore facilities included six circular concrete tanks, 12 m in diameter and 2.5 m deep, with four more to be built. The fish will be reared for approximately 1 yr in these tanks before they are acclimated to seawater and transferred to the floating net enclosures. This year, since the project was just beginning, the fish were raised at another location and were brought to Karakuwa for acclimation to salt water and transfer to growing pens. A system of large plastic pipes makes it possible to drain each of the large round tanks to transfer the 14,000 trout which will be acclimated in each tank into a long drainage channel which takes them to the shore where they can be transferred through pipes into the floating pens.
The floating pens are anchored in Ogatsu Bay which is well protected from storms by steep hills. The water in this area is 10-30 m deep and varies in temperature from above 8°C during the winter to a maximum temperature of 23-25°C during the summer.
The fish are fed ground raw fish and meal, making a product similar to Oregon moist pellets which is used in U.S salmon hatcheries. This food has been found to be better than dry pellets.
Only female trout are used in this type of culture as they are more disease resistant and are easier to acclimate to seawater than males. Also, females can mature in the sea in 2 yr producing healthy viable eggs, whereas males require fresh water to become mature. The sorting of male trout from female trout at a size of 18 cm is a time consuming operation.
The price of marketable trout 1.5-2.0 kg in weight is 450-550 yen ($1.46 to $1.79) per kilogram in the Tokyo fish market. This is about the same price as yellowtail Seriola, whereas smaller rainbow trout which weigh 150-200 g each sell for 250-300 yen ($0.81 to $0.97) per kilogram. In comparison, salmon from natural production sell for 600-800 yen ($ I .95 to $2.60) per kilogram.
One of the problems of raising rainbow trout in net enclosures is that they have tender skin and may lose some scales rubbing against the netting which may permit the entrance of the bacteria Vibrio. Japanese scientists have found that adding 10 ug of testosterone per gram of food will increase the mucous production in skin which will protect the scales from erosion. It is unlikely that testosterone could be used in the United States for this purpose because it is considered to be a carcinogen.
Another trout, Salvelinus plavius, known as the steelhead, is being reared experimentally in seawater at the Miyagi Prefectural Field Station at Ogatsu Bay. According to Koganezawa, S. plavius spawns in the headwaters of streams, is very resistant to changes in temperature, and can be successfully acclimated to seawater. Therefore, this is considered a good species for aquaculture, although it is not reared commercially at the present time.
The first Japanese pilot-scale experiments in culture of salmon in floating net pens in the marine environment are being conducted at Yamada Bay in Iwate Prefecture. Yamada Bay is completely enclosed except for a narrow entrance where the water is reported to be 90 m deep. Hills protect the inner bay from storms making it an ideal location for aquaculture. The Bay is about 60 m deep in the center, but 15-25 m deep in the area where the salmon culture rafts were anchored.
The objective of these experiments at Yamada Bay which was visited in October 1971 is to perfect methods which could be used commercially to rear salmon to marketable size in the sea.
The first experiments were with the chum or dog salmon, Oncorhynchus keta, which had been hatched at Fishermen's Cooperative Association hatchery at Miyako Bay just north of Yamada. This hatchery which is located on the Tsugaruishi River has a capacity of 50 million eggs and is one of the many hatcheries operated by local Fishermen's Cooperative Associations. These hatcheries take eggs from chum salmon in November, December, and January when the fish enter the streams, or occasionally from those salmon which are caught in trap nets in the bays. After the eggs hatch, the fry are reared until April in an effort to reduce the mortality of fry which they estimate as 50% in the streams plus a significant mortality during the month which the fry spend in shallow bays before going to the sea.
The eggs used in the experiment at Yamada were hatched on 22 February 1971 and began feeding on 8 April. They were held at the hatchery at Miyako Bay until 10 May because the holding tanks at Yamada had not been completed. After transfer, the salmon were held in fresh water at Yamada until 28 May when the seawater system was completed. Transfer to salt water was accomplished in about 24 hr with no significant mortality.
Because of the delay in completing the floating net enclosures the small salmon were held in seawater in tanks ashore until August when the temperature in the tanks reached 25.8°C. They were then transferred to the sea, but even there temperatures reached 24.4°C. These temperatures were too high and the mean survival was only 42%, although individual lots had survivals as high as 90%.
According to Chikara Iioka, who is in charge of this Iwate Prefectural Experiment Station, they will normally rear the salmon in fresh water until June or July and transfer them into floating net pens before midsummer. Even so, it appears likely there will be significant mortalities from diseases such as Vibrio since surface water temperatures usually reach a maximum of 22°C according to Iioka. Furthermore, the thermocline is deep in this area, according to Iioka's measurements, and the maximum temperature difference between the surface and a depth of 60 m is less than 4°C. In midsummer there appears to be only 1°C difference between the surface and bottom at a depth of 15-25 m where the salmon culture pens are anchored.
National Marine Fisheries Service experiments with salmon culture in Puget Sound, Wash., have indicated increased mortalities due to Vibrio when seawater temperatures exceed 15°C. On this basis it appears likely that the high summer temperatures at Yamada Bay wll be a limiting factor to salmon culture unless methods can be developed for preventing or reducing Vibrio infections.
Three kinds of net enclosures were being tested by Iioka and his associates. One type was a floating net pen similar to those used for the culture of trout or yellowtail, but with some refinements in the design. These enclosures were about 6 or 8 meters square and about 3 m deep with nearly 1 m of the sides above the surface of the water. The tops were covered with a coarse mesh to exclude birds and the sides and bottoms were made of about 8 mm square mesh. These enclosures contained 4,000 young salmon which by October had reached a length of 20-25 cm. Another similar pen contained 300 2-yr old salmon which appeared to be about 40-50 cm in length. Iioka reported that these floating surface pens were satisfactory except that the nets had to be changed every month because of heavy fouling by seaweeds.
The second type of enclosure was a middepth pen which was located at a depth of 10 m to the top of the net. The enclosure was 10 meters square and 7 m with a top and bottom. Even at this depth the heavy growth of seaweed required changing the net about every 3 mo.
The third type of enclosure was a large octagonal net 55 m in diameter which extended from the surface to the bottom and was anchored in position. The net was supported by a series of floats at the surface and held in contact with the bottom by a lead line.
A horizontal section of fine mesh at the surface extended inward about 3 m from the vertical walls and the inner border was supported by net floats placed about 4 inches apart. Iioka had found that the fish made no attempt to jump over the inner row of floats and indeed found refuge and shade under the floating section of the net which rapidly became fouled with seaweeds.
Feeding was accomplished by rowing a boat over the top of the net into the center of the pen where the food was thrown into the water.
Predation by diving water fowl was prevented by stretching twisted bright-colored plastic tape, 11/2 to 2 cm wide, across the enclosure at intervals by tying it to vertical supports so that it was about 1 m above the surface of the water. The apparent movement of this tape caused by the wind seemed to scare the birds away. The same system is used to keep birds away from the rice fields.
The young salmon were fed a dry pellet food that had been developed for feeding rainbow trout in the sea, and this was found to be fairly satisfactory. The fish were fed 3 times a day, and the pellets were mixed with water before feeding. The Japanese scientists stated it is important to mix the food with fresh water so that the fish have a source of fresh water to replace that which they would normally receive by eating other fish.
The objective of the Yamada Experimental Station is to develop methods for commercial salmon culture so a number of experiments are in progress or planned. Experiments by Koganezawa et al., reported in 1968, indicated that chum salmon grow more rapidly in brackish water than in fresh water or salt water. These experiments are being repeated at Yamada to develop procedures for increasing growth rate during the time that the fish are held in tanks on shore.
Also, next year Iioka and his associates plan to transfer chum salmon fry to salt water at various ages from 9 to 90 days in order to determine the optimum time. They also would like to test other species, such as the pink salmon, O. gorbusha, and the king or chinook salmon, O. tshawytscha, from Hokkaido, and possibly the coho salmon, O. kisutch, from the United States.
In summary, the Iwate Prefectural salmon culture station at Yamada is located at a delightful place for experimental aquaculture. The only limiting factor appears to be the high temperature of the water during the summer and the adverse effects of this may be overcome by selection of species or races of salmon, use of hybrids, or treatment to prevent or alleviate the effects of Vibrio and other diseases which are accelerated by high temperatures. Both domestic and export demands are excellent and it appears probable that commercial salmon culture in the marine environment will be economical.
FUJIYA, M.
1970. The present status of marine fish cultivation research in Japan. Helgolander wiss. Meeresunters. 20:594-601.
1970. Studies on the early life history of the rainbow runner, Elagatis bipinnulatus (Quoy & Gaimard) in the Indo-Pacific Oceans. [In English, Japanese abstr.] Bull. Far Seas Fish. Res. Lab. 3:167-186.
1 Deputy Regional Director. Northwest Region. National Marine Fisheries Service. NOAA. Seattle. WA 98109.