RIASSUNTO
ABSTRACT:
In the case of rearing some kinds of fishes that have hiding behavior in the floating aquaculture preserves, a number of fish decreases due to the stress from irregular movement of floating preserves caused by the irregular and continuous ocean waves. Therefore, we developed one method that can reduce the movement by absorbing wave energy. The principle is that natural frequency of oscillating water column is determined not by its volume but by its length. We examined the restraint function of this method in the real sea area in this study.
INTRODUCTION
In recent years, contaminated foods have become a growing concern in Japan. Production of fish is expected to increase because of expanding demands for safer foods derived from fears of BSE, bird flu and swine flu in health-conscious consumers. Growing demand for fish has been spreading not only in Japan but also all over the world. While demand for fish is expected to increase, Japanese fish self-sufficiency rate is still low. According to the Ministry of Agriculture, Forestry and Fisheries, Japanese fish self-sufficiency rate steadily decreased after peaking at 113% in 1964 and it fell below 60 % in 1994(Japan Ministry of Agriculture, Forestry and Fisheries, 2009). In order to meet this high fish demand, improvement in fishery yield is necessary. In Japan, central and local governments have conducted farming fisheries such as releasing of large number of fish juveniles for better fishery catch. We have been releasing 2 species that have hiding behavior, such as red spotted grouper and Oblong rockfish in the Seto Inland Sea. However, survival rates were less than 1 % due to high predation pressure and their fragile nature. As a result these fish are considered very rare in the Seto Inland Sea and traded at high prices.