EXPERT TOPIC AMBERJACK
INTRODUCTION AMBERJACK
EXPERT TOPIC
Japanese amberjack (Seriola quinqeradiata) culture began in 1927 in the Kagawa prefecture of Japan where wild juvenile amberjacks were first reared in shore enclosures. Waste accumulation and poor water quality led to this type of culture becoming swiftly obsolete, and so refined commercial production began in the 1940s, which expanded rapidly in the 1960s. By 1970, amberjack production was exceeding 43,000 tonnes, reaching a peak in 1995 of nearly 170,000 tonnes. The industry hit a record height in the late 1990s, where production reached between 132,000 and 160,000 tonnes.
Plentiful production
Japanese amberjack features in the fisheries of the Western Central Pacific Ocean, from Japan and the eastern Korean peninsula to the Hawaiian Islands, but its farming occurs primarily in Japanese waters. The Republic of Korea is the only other country reporting production to the Food and Agriculture Organisation (FAO). The aquaculture production of Japanese amberjack constitutes over 50 percent of the total farmed marine finfish production in Japan, a surprisingly high amount when considering the rarity of this fish in the Western market. Amberjack can be eaten as sashimi or grilled when sold as fillets. It has a firm white, mild tasting flesh. The common name of Japanese amberjacks varies with size. Those that weigh under 50g are called ‘mojako’, whilst those
by Matt Holmes, Features editor, International Aquafeed weighing between 50g and 5000g are named ‘hamachi’. ‘Buri’ is the name granted to the amberjack which weigh in at over 5000g. These fish spawn along the 200 mile contour in the East China Sea, juveniles migrating north towards Hokkaido, where they feed for three to five years until reaching sexual maturity, when they migrate south for spawning. Adults of 70-80cm approach the western coast of Kochi prefecture, Japan, in March-April. From season to season, various sizes can be caught in different parts of Japan. The optimum rearing water temperature for Japanese amberjack is 20-29 ºC and the optimum salinity is 30-36 percent. Aquaculture of amberjack is primarily dependent on seed supply from the wild, although imported seed is also available from the Vietnam and the republic of Korea. Soon after spawning, larvae less than 15mm long are brought near the coast by the Kuroshio Current, where they are caught in fine mesh nets, and sold to fry specialists. Although artificial propagation of Japanese amberjacks has been successful, the number of juveniles produced through induced breeding has not yet reached a level where it can make a significant contribution to the demand of juveniles for aquaculture. In fact, there remain some problems in larval rearing: feeding is particularly critical, as imbalanced larval feed leads to heavy mortalities. Efforts are being made to improve this situation. The design of suitable larval feed by using mass-produced food organisms, such as rotifers and brine shrimp nauplii fortified with n-3 highly unsaturated fatty acids (HUFA) and formulated feeds, may soon make the production of healthy fry in large numbers possible.
38 | November 2018 - International Aquafeed