Characteristics of Deep Seawater Drainage and Its Recycling

Abstract

In Toyama Prefectural Fisheries Research Institution, deep seawater (DSW) has been used for aquaculture of cold water/deep-sea species of fish, prawn and shellfish to be drained as various drainage. These drainage were thought to still have the basic characteristics of DSW without greatly changes, as DSW contacted with living thing only once for a short time.
In order to utilize DSW more effectively, characteristics of the drainage were examined, and experiments re- and multi-use of DSW for aquaculture were carried out. As for characteristics of the drainage, water temperature and the level of dissolved oxygen somewhat varied, and the number of microorganisms slightly rose in the drainage as compared with original DSW, but chemical oxygen demand, pH and salinity was stable. These results demonstrated that the quality of drainage wasn't hardly different from that of original DSW, and the drainage can be applied to aquaculture. The survival rate of pacific cod raised in the DSW (first use) and in the drainage (second use) for 84days was 95% and 75%, respectively.
Then survival was lower in the second and third use. In the connection, further investigation including growth rate was necessary because survival rate greatly depends on various factors and conditions during culture. When the drainage is used, great attention must be paid to infection of fish disease.