Red Sea Bream Aquaculture- Is Deep-Sea Farming the Solution?

9 December 2016, at 12:00am

JAPAN - Red sea bream has a special place in Japan. Known as madai in Japanese, its unique red colour is considered lucky, and the fish is often served whole on New Year's Day, wedding ceremonies and other auspicious occasions. In aquaculture, it's one of Japan's most important commercial fish, and the coastal city of Uwajima in southern Ehime prefecture is playing a key role in rearing the species. Bonnie Waycott visited seafood and aquaculture firm Dainichi Corporation in Uwajima to see how red sea bream is being raised.

Since its establishment in 1982, Dainichi has made full use of the nearby Uwa Sea to farm various species over the years such as bluefin and yellowtail. Mr Takeo Matsushima, Chief Operating Officer at Dainichi, believes that this stretch of ocean has been key in guiding the company to success.

"Uwajima is blessed with a rugged, indented coastline, deep bays and calm seas that are home to many offshore cages," he explained.

"The area from the mountains to the sea is just like a series of cliffs, and nutrients flow easily into the water. Close to land, the sea is also extremely deep with currents, which helps prevent problems like eutrophication. The bays are sheltered and often unaffected by typhoons. For aquaculture, conditions couldn't be better."

Thanks to its deep depths, the Uwa Sea has also helped Dainichi try its hand at a new kind of aquaculture - the deep-sea farming of red sea bream. Because red sea bream usually live in deeper waters, Dainichi felt it was well positioned to rear the species in conditions close to their natural environment. Since coming up with the idea about thirteen or fourteen years ago, the company has never looked back.

"It took several years for production to stabilize," explained Mr Kanji Tsurukawa, Assistant Manager of Dainichi Corporation's Aquaculture Technical Division.

"But now our red sea bream is sold across Japan and abroad for 1.2 - 1.5 times the price of ordinary red sea bream. We market it as Shinkai Madai, or deep-sea red sea bream."

Raising fish at deeper depths has many advantages. For example, the high water pressure results in denser muscles and thick, firmer flesh with a chewy texture, while ultraviolet rays can't penetrate deeper waters so this prevents melanin generation and gives red sea bream its bright red colour. The fish are also safe from sudden fluctuations in temperature or changes at the water surface such as high waves.

Fry from a nearby hatchery are delivered to Dainichi by boat and put into an offshore cage, where they are reared until they reach 300g. At this point, they are moved to another cage and raised there until they reach 800g - 1kg. They are then moved to a third cage, where they stay until they are ready for shipping at 1.8 - 2kg. As they grow, the fry are given extruded pellets (EP) that are low in fat and high in protein.

Six months before the fish are due to be shipped, when they weigh around 1.3 - 1.6kg, they are lowered to deeper depths of around 50m and fed through a feeding hose.

After six months, they are raised to shallower depths. The procedure takes around two days and must be done slowly and carefully as the sudden change in water pressure can burst the fish's swim bladders. The fish are then monitored through a small underwater camera that is attached to a hose and lowered into the cages, while hand-held monitors are used on land for observations. When they're close to the water surface, they are fed shrimp meal, squid meal and fishmeal such as sand lance (ammodytes personatus).

The shrimp meal is a powder with antioxidants and astaxanthin, a carotenoid that gives the fish its colour. The squid meal contains glutamic acid and helps in the production of digestive enzymes.

"When the fish are at the surface, we watch them constantly to see how they behave. Then we decide how often they should be fed, and how much," explained Tsurukawa.

"If they are thrashing about, we'll give more feed. Usually we'll give about 400kg a day but we have to remember that factors like water temperature and weight will also determine how much they eat. We need to make sure we are giving the right amount and that the feed isn't accumulating inside the cages."

Dainichi ships 80,000 red sea bream, or 6,000 to 7,000 fish a month, across Japan. Its main clients are restaurants, department stores and food-related industries. The fish are also shipped to wholesalers in southeast Asia, the Middle East, the US and Europe.

"We'd like to make even further inroads abroad," Tsurukawa said. "In Japan our red sea bream has a very good reputation, so much so that I'd like to think it's the most well-known here and we'd like to see that happen in other countries as well. If we can continue to provide an environment with conditions that support the growth of red sea bream, we could be an industry that is even more prosperous for the Ehime region and beyond."

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