The most popular rearing systems used in Japanese amberjack culture in Japan are floating net cages or pens (Glude 2003; Nakada 2002).

Japanese amberjack culture began in Japan in the 1920's with the use of net and embankment-enclosures (Glude 2003; Nakada 2002). As culture operations expanded, red tide episodes, poor water quality and waste accumulation associated with these embankment-type methods required farmers to adopt the floating net pens and cages in use today (Nakada 2000). Although localized pollution is also problematic for floating net pens and cages, advantages over embankment enclosures include improved water exchange and flushing, lower maintenance costs, and easier harvest techniques (Benetti et al. 2005).

The typical pen size for Japanese amberjack is 15 x 15 x 15m, but larger pens up to 50 x 50 x 50m are also used (Nakada 2000; Benetti et al. 2005). There is a preference for larger pens which allow the fish to develop high quality meat with proper fat levels (Nakada 2000; Ottolenghi et al. 2004).

Japan is the main producer of farmed Japanese amberjack, producing over 99% of global production in 2000 (Ottolenghi et al. 2004). Farmers also rear the species in the Republic of Korea and Taiwan (Ottolenghi et al. 2004).

Stocking density ranges from approximately 4 to 26 kg/cubed meter, depending upon the size of Japanese amberjack being reared and the size of the rearing environment (Nakada 2000).

There are three size divisions in farmed Japanese amberjack operations: mojako weigh less than 50g (2 oz); hamachi weigh between 50g and 5kg; and buri weigh greater than 5kg (approximately 11 pounds) (Nakada 2000). Rearing densities for these size classes, as defined by Nakada (2000), are: mojako 10,000-30,000 fish for a 5x5x5 meter pen (4.3 to 14.4 kg/cubed meter); hamachi 14,000 to 20,000 fish for a 8x8x8 meter pen (11.1 to 26.0 kg/cubed meter); and 3,500-7000 fish for buri reared in 10x10x10 meter pens (17.0 to 13.6 kg/cubed meter).

High density culture operations are now common to compensate for falling profits (Nakada 2000; Benetti et al. 2005; FAO 2007). Falling profits are attributed to a combination of factors including a stagnant Japanese economy, high competition among Japanese amberjack farmers, increasing feed costs, increasing mojako/seed supply costs, declining consumption by Japanese youth and a lower market price for Japanese amberjack (Nakada 2002).

Automatic feeding systems and polyculture have been identified as promising strategies to reduce the environmental impacts of Japanese amberjack farming (Nakada 2000, Benetti et al. 2005).

Nakada (2000) promotes a comprehensive culture approach, including the use of lugworms to consume organic material in mud and growing algae to absorb excess nutrients in the vicinity of Japanese amberjack culture.

Also under research are two additional technologies that would greatly improve the environmental effects of farming: rearing Japanese amberjack in closed, land-based aquaculture facilities and the artificial propagation of the fish in hatcheries. Successes have been achieved in both of these technologies, but they are not yet economically feasible when performed at a large scale (Nakada 2002).

Points are not awarded for these innovations since they do not appear to represent the farming practices of most operations.

As a carnivorous fish, Japanese amberjack require high content of fishmeal, with about a 40% fishmeal inclusion rate (Stevens, pers. comm., 7/8/04).

During the early development of Japanese amberjack culture, farmers relied on trash fish such as Pacific sandeel, anchovy, chub mackerel, sardine, and Pacific saury (FAO 2007). Eventually this practice gave way to using sardines as the main feed source. Sardines were cheap, abundant and reduced food waste and deterioration of culture grounds when given in frozen form to farmed Japanese amberjack (Nakada 2000).

In the early 1990s farmers began using moist pellets and dry extruded pellets more frequently due to an increasing awareness of environmental degradation of culture grounds (Nakada 2000). The increasing use of moist and dry pellets in the last 20 years is also related to the decline of spotlined sardine (Sardinops sagax) abundance (Nakada 2002) and the lower cost of formulated feeds compared to raw fish (Benetti et al. 2005). However, fish products are still the primary protein source in Japanese amberjack feed.

The FCR varies with the type of feed and the size of fish, ranging from approximately 15-20 for minced raw fish, 3.5 to 15.0 for moist pellets, 3.0 to 6.5 for high-fat dry pellets, and 0.8 to 3.5 for dry extruded pellets (Nakada 2000).

Juveniles are typically fed dry extruded pellets during their first year of culture (FAO 2007; Benetti et al. 2005) with FCRs as low as 1.2 (Benetti et al. 2005). However, larger Japanese amberjack (>3kg) prefer raw fish to dry extruded pellets (Benetti et al. 2005). Raw fish is also often used during times of low water temperatures when feeding diminishes and growth is slowed or delayed (Benetti et al. 2005; FAO 2007).

The Japanese government and private sectors are researching methods to reduce fish content in feeds.

Research is underway to use alternative protein sources as well as to develop pellet type foods that satisfy the nutritional needs of larger Japanese amberjack (Nakada 2000; Nakada 2002). By perfecting the amounts of fishmeal and fish oil in pellet foods producers may expect to pay lower costs than those continuing to use minced fish, such as anchovies or sardines.

Research has shown that substitutes can be used to cut the amount of fishmeal and fish oil in Japanese amberjack feeds in half without adversely affecting growth rates or culture production (Nakada 2000). Soybean meal or poultry meal is expected to eventually replace fishmeal in formulated feeds (Nakada 2000).

Although FCRs less than 1.3 can be achieved when giving juvenile Japanese amberjack dry pellet feed, the FCR for larger individuals, which are fed raw fish, is much higher.

Most Japanese amberjack farming operations use net cages in sheltered bays (Nakada 2000; Nakada 2002; Glude 2003), rendering effluent treatment impossible. Effluent sources include unconsumed feed waste, medicines, chemical cleaners, dead fish, and biological waste.

Japanese amberjack aquaculture operations are known to adversely affect water quality by causing waste accumulation, red tide outbreaks, eutrophication and hypoxia.

A major concern is the accumulation of feed waste in the vicinity of net pens. Studies published in 1991 by Watanabe indicate that high percentages of feed are discharged into the areas surrounding Japanese amberjack farms. Using a moist pellet diet, 74% of feed is discharged into the environment (19% as unconsumed feed waste and 55% as fish excretion). Percentages are higher when using raw fish feed: 85% of the feed is discharged (72% by unconsumed feed waste and 13% by fish excretion) (Katsuyuki and Yokoyama 2007). Waste accumulation can lead to red tides, nutrient loading and hypoxic conditions.


Eutrophication, which results from phosphorous and nitrogen loading in the vicinity of Japanese amberjack farms, has been linked to the occurrence of red tides in Japan (Anderson and de Silva 1997; Nakada 2000). These red-tide occurrences date back to the mid-1950's. In 1970 a severe red tide of Chattonella antiqua caused the mass mortality of half a million yellowtail fish valued at over 620 million yen. Since that time, red tides caused by Chattonella spp., Heterosigma spp., and Cochlodinium polykrikoides have continued to result in the loss of millions of dollars to the Japanese amberjack farming industry (Ottolenghi et al. 2004).

The large amount of waste produced during intensive fish farming practices, such as the case with Japanese amberjack, can also result in localized oxygen depletion. Oxygen is consumed as bacteria decompose feed waste, fish excretions and other organic materials settled beneath the fish cages. During colder months, this oxygen-depleted water can rise to the surface, killing fish in the cages (Ottolenghi et al. 2004, Benetti et al. 2005).

The waste produced by high-density Japanese amberjack culture has been linked to the rise in parasites and other harmful organisms in the areas surrounding farming operations (Nakada 2000; Nakada 2002).

Net pens clogged with algal growth are typically cleaned with copper-based anti-foulants (Ottolenghi et al. 2004). Tri-butyl tin (TBT) was used in the past to treat cage growth but has since been banned due to toxicity risks (Ottolenghi et al. 2004). Pesticides such as Tremaclean or Bitin are also used (4,5-dichlorophenol) (Glude 2003).

Antibiotics are widely used for bacterial infections and other drugs are used to treat parasitic diseases (FAO 2007). These medications are often mixed with moist or dry-pellet feeds (Nakada 2000), as are supplements and vitamins (Nakada 2002), and likely leach into the water after feedings.

In 1999 Japan introduced new legislation (the Law to Ensure Sustainable Aquaculture Production) to address the environmental sustainability of aquaculture, including Japanese amberjack farming (Ottolenghi et al. 2004). This legislation includes new water quality and sediment monitoring requirements.

The aquaculture law sets criteria to identify 'healthy' and 'critical' farms based on thresholds for dissolved oxygen in fish cages, health of macrofauna beneath cages, and sulfide content below cages (Katsuyuki and Yokoyama 2007).

The Law to Ensure Sustainable Aquaculture Production also promotes local cooperatives to develop voluntary plans to improve pollution at culture grounds and implement disease prevention measures. This system is gaining popularity, with 80% of all aquaculture sites (not just those rearing Japanese amberjack) participating in the program (Ohashi 2006).

Benetti et al. (2005) note the implementation of some measures to reduce environmental effects of Japanese amberjack farming such as 'dredging accumulated bottom sediments, the use of chemicals to stimulate decomposition of organic matter, the prohibition of minced raw fish as feed, and prohibiting the culture of large yellowtail in favor of culturing smaller, less polluting fish'. It is unclear, however, how frequently these controls are actually used by farmers.

Japanese amberjack farmers can reduce the amount of pollution or disease outbreaks in waters surrounding net pens by using specialized pellet feeds, which do not produce waste products laden with excess indigestible fatty acids (Nakada 2000). We do not add points here because it does not seem low-pollution feeds are currently in common use.

Nakada (2002) notes the use of automatic feeding systems as a promising technology that may help in the near future to reduce waste accumulation and its associated pollution and disease risks.

Japanese amberjack farming operations in Japan and Korea are within the natural range of the species (Fishbase 2007). Escape frequency is unknown.

As Japanese amberjack are farmed in open net pens in their native areas, escapes are likely to survive in the surrounding ecosystem.

Japanese amberjack is known to be affected by a number of bacterial, viral, and parasitic diseases and likely transmits these diseases to wild populations. Viral diseases include Iridovirus and Yellowtail Ascite Virus; bacterial diseases include vibriosis (infection by Vibrio anguillarum), pseudotuberculosis (infection by Pasteurella piscicida), streptococcus (infection by Enterococcus seriolicida); and parasitic diseases include flatworm and trematode infections from Benedenia seriolae and Axine heterocerca (Ikenoue and Kafuko 1992; Aoki 1994; Nakada 2000; FAO 2007). The warm water disease ciguatera has also been an issue in yellowtail rearing (Nakada 2000).

In recent years, drug resistant strains of bacteria, particularly those causing streptococcus and pseudotubuerculosis, have become a serious issue (Aoki 1994).

Operations to limit the effects of escaped farmed fish are unknown, however it is not likely that escaped individuals compromise the ability of wild species to utilize natural resources. Because farmed Japanese amberjack are taken from the wild population as seedlings, they pose no threat to wild populations through interbreeding and genetic interaction.

Nakada (2000) notes that managers and farmers lack appropriate counter measures to control diseases in intensely farmed fish. However, protocols are in effect to minimize outbreaks when they do occur. Treatments vary with the type and source of disease and often include oral administration of antibiotics and sulfa-drugs for bacterial infections and fresh water dips (often with parasiticides) for parasitic infections.

Minimizing the likelihood of disease outbreaks, and their effects when they occur, is best achieved by maintaining healthy environmental conditions at the farming site and the ability of a farmer to anticipate when and what type of disease will strike (e.g., when water temps rise above 28 degrees Celsius). This allows implementation of preventative measures such as reducing stocking densities and feed amounts, and identifying sick fish soon after they are infected (Nakada 2000; FAO 2007).

Operations in Japan occur along the coast in sheltered bays (Glude 2003), primarily in central and southern Japan (Ikenoue and Kafuku 1992). Over 80% of culture production (based on 1999 data) occurs in five prefectures located in southwestern Japan. These are Ehime, Nagasaki, Kagoshima, Oita, and Kouchi prefectures, with Ehime comprising the largest portion of the overall production (Nakada 2000).

Research on farming Japanese amberjack offshore or in land-based closed systems has proven successful in rearing high-quality meat in a low pollution environment, but this method is not considered economical for large-scale operations (Nakada 2002). Benetti (2000) states that offshore cage farming of yellowtail species (Seriola spp.) may be an ecological and economical option in the near future.

Japanese amberjack juveniles called mojako are taken from the wild to stock farms. Mojako live in or near floating seaweed and are often captured in this environment or as they disperse from the seaweed and head towards the shore (Nakada 2002). The wild mojako are caught by licensed fishermen with hand nets or round haul nets (Ikenoue and Kafuku 1992). Despite measures by the Japan Sea Water Fishery Cultivation Association to limit the number of mojako caught each year (Nakada 2002), relying on wild fry is likely detrimental to the wild population (Owens, pers. comm. 7/7/2004).

The Japanese Fishery Agency introduced regulations in 1966 limiting the annual capture of mojako to approximately 40 million, which is distributed via a quota system to prefectures by the Japan Seawater Fishery Culture Association (Nakada 2000). Annual capture of mojako has fluctuated with a high of 45 million in 1977 and a low of 25 million in 1997 (Nakada 2000). Even in years of low mojako abundance, farmers have been able to maintain production. This is possible due to supplemental imports of mojako from Korea and technological advances in prepared feed which has increased the survival rates of mojako (Nakada 2000).

Despite fluctuations in available wild mojako and the increasing dependence on foreign supply, there does not appear to be any indication that the Japanese government will reduce or otherwise revise the 1966 regulation allowing for the annual capture of 40 million juveniles.

Artificial propagation of Japanese amberjack in hatcheries has been intensively studied in recent decades with notable successes. The species spawns easily in captivity, and eggs are also obtained from wild and cultured broodstock. However, the high juvenile mortality rate (attributed to disease, nutrition, and egg quality factors) has been a roadblock to the mass production of hatchery-produced individuals (Benetti 2000). Studies continue and advancements are expected to allow for mass production of hatchery raised Japanese amberjack in the future.