Sea Technology

AUG 2017

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www.sea-technology.com August 2017 / st 23 T he global demand for fishery products is rapidly increasing. There will be an annual fishery prod- uct shortfall of 92 million tons by 2030, according to the Food and Ag- riculture Organization of the United Nations. The production of fishery products through aquaculture is ris- ing in response to this growing de- mand. As of 2014, aquaculture account- ed for approximately 44 percent of global fishery production, and 21.8 percent (480,394 tons) of that was in South Korea. As with other industries, however, the rapid growth of the industry has led to problems related to the envi- ronment. With the continuous growth of aquaculture facilities in coastal wa- ters, contamination from high-or- ganic loads due to intensive farming and the long-term use of fish farms have severely affected coastal marine environ- ments and marine ecosystems. In South Korea, aquaculture facilities are concentrated on the southern coast. Conse- quently, South Korea's coastal waters have been polluted by many anthropogenic sources that affect the dissolved oxy- gen (DO) levels. The DO levels within an inshore fish farm can be as low as 40 percent (4.0 mg/L). These low DO levels limit the pro- duction of many aquaculture species because they stunt growth by limiting the scope of the aerobic metabolism. As the intensity of farming increases, the DO level and its im- pact on the growth of fish will become more important to farmers. The specific growth rate is significantly affected by hy- poxia. Therefore, to expand aquaculture operations, using more exposed, often underutilized sites with better DO ex- change rates is an option. However, those areas of the sea where such offshore cage facilities are installed are exposed to stronger tidal currents and waves than the inshore areas, affecting the safety of the facilities and causing the shape of the cage nets to change. This change in the shape of the cage net stresses the con- tained fish and negatively affects the growth environment. Therefore, a new cage system is needed that is capable of maintaining its shape in an offshore environment. This study set out to develop a cage system using a copper-alloy net and installed it near an existing offshore synthetic-fiber cage system to verify the possibility of using it in the open sea. Furthermore, the applicability of a sonar system to the measurement of the underwater behavior of the cage system was examined by analyzing the change in the shape of the cage under the influence of tidal currents. In addition, experiments were conducted on the growth of sessile organisms on both fiber and copper-alloy nets out at sea to verify the effect of the copper-alloy nets on the inhibi- tion of the growth of sessile organisms. Aquaculture Design For Healthier Fish Fish Cage with Copper-Alloy Net Improves Fish Welfare By Dr. Jihoon Lee • Dr. Bokyu Hwang • Dr. Mooyoul Choe The fish cage system with copper-alloy netting.

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