IWMC.org - 2nd Symposium - Issues of Relevance

Japan's Efforts on Technological Development for Sustainable Marine Aquaculture Tohru Morikawa President, Overseas Fisheries Consultants Association, Japan

A private company developed different type of large scale offshore aquaculture system which is called "AQUA SYSTEM". During a test the facility was struck by three big typhoons. There was no damage on the floating structure, however, cage nets were broken by rubbing with the inside of floating structure. The damage of cage net caused by difference of the movement between cage net and floating structure. They still working on engineering better system. To solve the problem of sharp decline in feed fish (mainly sardine for fish meal), Japan is developing a new type of feed using substitute protein such as soybean cake, corn gluten and feather meal for fish meal. According to the results of experimental culture of yellow tail using new feed containing only 20% fish meal (normally more than 50%) by adding 30% of another protein, the growth rate of fish reared with new feed was 92% of that obtained with general fish meal compounded reed, and feed efficiency was 84% of general feed. Moreover, the appearance of the fish and the taste, colour and quality of fresh meat was better than those of fish reared on fresh fish feed or moist pellet. There are strong prospects of using less fish meal content feed in the future, and also contribute to avoiding sea pollution and rational utilization of valuable marine living resources as food directly for mankind.

One of the important technological advances in healthy seed production is the development of no appropriate formulated micro-diet and a mass production system for micro organisms such as rotifers for the feed of early culture.

In order to improve culture stability and to reduce labour and space for the mass production of the marine rotifer, a continuous culture system has developed to produce 2 -3.5 billion rotifers per day continuously and reliably with only 1,000 litre culture system. Production capacity of this system is equivalent to the production of 20 tons batch tank culture. Continuous mass-production system is composed by sea water filtration system( sea water supply), feed (chlorella) supplying system (feed tank), rearing tank and harvesting tank.

As for the development of micro particulate artificial diets, it is possible to replace 2/3 of live micro-organisms with artificial micro diets without affecting the survival rate of sea bream fish as shown in upper graph. Vitality of sea bream juveniles fed with artificial micro diet have been found to be more strong. Artificial micro diet is easy to enrich the nutrition required in early rearing period of juveniles as compared to micro organisms diet. Same results from the test of striped-jack juveniles.

One of the tasks remaining in this area is to determine how to prevent pollution of rearing water by artificial feed.

Increasing the number of cultured species is also important to establish a stable aquaculture industry giving full attention to the consumer's needs and preferences. The Japan National Fish Farming Centre has been developing technology for artificial fish fry production of new species. Many agencies engaged in aquaculture have been trying bluefin tuna cage culture since more than ten yeas and effective culture system has been developed recently.

Japan National Fish Farming Centre had started the sea farming study on the northern bluefin tuna utilizing 40 m diameter circular pen in Amani, Okinawa and 367 bluefin tuna from 2 years class to 11 years class are rearing now.

In 1998, 5, 10 and 11 year class blue fin tuna had spanned 200 million eggs and about 200 young tuna of 30 cm size were produced from the eggs in the cage. From these 200 tuna, 111 young tuna of 30 cm size were experimentally released in the sea with tag and 50 reminder are rearing continuously at the station successfully in 1998.

IWMC World Conservation Trust