The coral trout, or leopard coral grouper (Plectropomus leopardus), is a colourful native of tropical and subtropical areas of the Indo-Pacific. In Japan, it’s mainly found in waters off Okinawa, where it's known as Akajin. It spends most of its juvenile and adult life in one area, and hides between hard corals and rocks or in shelters that it excavates on the reef floor. Some species can reach up to 300kg in weight and up to 2.7m in length.
Coral trout numbers are decreasing due to changes in their habitat – such as coral bleaching, in which stress factors such as rising sea temperatures or overfishing cause coral to lose its colour and begin to starve.
But another reason for the coral trout’s decline is its economic value. A favourite target for fisheries worldwide, the market price and demand for coral trout are currently very high. In places such as China, Singapore and Taiwan, the species is traded as a luxury product, and those with a strong red colour fetch a particularly high price, such as 20,000 Japanese yen (around £142) a kilogram.
The FRA succeeded in the complete farming of coral trout this autumn. Established through a merger of the Fisheries Research Agency and the National Fisheries University, the FRA aims to intensify research and development as Japan’s only comprehensive fisheries R&D organisation. Its success in coral trout farming has led to hopes for a safe and stable production process that could protect natural stocks and create breeds with advantageous traits.
Coral trout aquaculture has existed in countries such as Australia and Vietnam since the 1990s, when fish were caught in the wild and raised to market size for export to places such as China and Taiwan. In Japan too, it is not entirely new. The FRA’s Seikai National Fisheries Research Institute (SNFRI), based in Nagasaki, began researching coral trout farming in 1985.
In 2009 it successfully produced seedlings from more than 30,000 fish and began experiments using these, but still had to obtain parent fish from the wild. Raising the larvae had its challenges:, coral trout have long spines that can become entangled and survival rates can be low.
The FRA made its breakthrough on 10 June 2016, when it obtained fertilised eggs from coral trout that had been born and raised artificially. These eggs were then used to artificially produce seedlings, and on 28 July 2016, 29,000 fry, each measuring 32.9mm in length, were born – almost a quarter survived to maturity.
The fry were raised in tanks on land, and moved to different ones as they grew in order to maintain an appropriate stocking density. Although the project is still at an experimental stage, the FRA is continuing its work in an attempt to produce future generations from its initial stock.
The FRA’s achievement demonstrates that coral trout can be bred in aquaculture facilities without the need to draw stocks from the wild. Once the fish have grown out, they can then be used to breed future generations of captive-bred coral trout, while it may also be possible to transfer growing techniques and expertise to commercial operating environments. Advantageous traits such as high growth rates or a bright red colour can be selected, while artificially managing the entire farming process from rearing parent fish to producing seedlings could lead to stable supplies.
With an increasing consumer base and growing affluence in places such as Hong Kong and China, the market for live seafood, including reef fish such as coral trout, seems set to increase for the foreseeable future – and the FRA hopes that its work could lead to a new market for farm-raised coral trout. It's planning to carry out experiments to produce around 10,000 fish weighing a shipment size of 500g. The fish will be shipped on an experimental basis, partly to assess the costs involved, while further research will be carried out into the conditions necessary to create a viable aquaculture industry for coral trout.
Although commercial production at scale has yet to be achieved, the FRA hopes its research will attract much interest in Japan and abroad. By sharing its knowledge and information in the future, it also wants to contribute to the advancement of aquaculture industries worldwide.