• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.63-69
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• 2011

In this paper, the wave forces on a cylindrical aquaculture fish cage, which consists of the porous mesh with the uniform porosity, are analyzed using matched eigenfunction expansion method. The boundary condition on the porous net is derived based on the Darcy's law, which implies that the velocity of the fluid passing through the net is linearly proportional to the pressure difference between two sides of the net. The wave forces and wave responses are investigated by changing the porous parameter of porous net as well as the submerged position (floating type, bottom-mounted type) of an aquaculture fish cage. It is found that the wave forces on a bottom-mounted type are largely decreased compared with that on a floating type. Also, the porosity of the netting structure plays an important role in reducing the wave forces and the wave elevation in the vicinity of an aquaculture fish cage.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.2
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• pp.159-168
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• 2010

This paper presents a mathematical model and simulation method for investigating the performance of set net systems and fish cage systems influenced by currents and waves. Both systems consist of netting, mooring ropes, a floating collar and sinkers. The netting and ropes were considered flexible structures and the floating collar was considered an elastic structure. Both were modeled on a mass-spring model. The structures were divided into finite elements and mass points were placed at the mid-point of each element, and the mass points were connected by mass-less springs. Each mass point was subjected to external and internal forces and the total force was calculated at every integration step. An implicit integration scheme was used to solve the nonlinear dynamic system. The computation method was applied to dynamic simulation of actual systems simultaneously influenced by currents and waves in order to evaluate their practicality. The simulation results improved our understanding of the behavior of the structure and provided valuable information concerning the optimized design of set net and fish cage systems exposed to an open ocean environment.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.190-196
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• 2002

In order to analyze the hydrodynamic forces on fish cage systems, made of frames and nettings, under waves and current, hydraulic model experiments for square type and circular type of fish cage system were carried out in a towing tank. Both cage systems consist of net cages supported by floating frames made of two concentric pipes and four weights hanging from the bottom corners of the nets. There was little difference in the hydrodynamic force on the square type of fish cage system by wave heading under regular waves and the peak frequency of the force on each cage system was in a good agreement with that of induced irregular wave. In addition, it was also observed that the circular type of cage system was more stable to the action of waves and current than the square type.

• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.4
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• pp.381-386
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• 2010

We have cultured the bluefin tuna in Yokjido, Tongyeong with floating cage which was vulnerable to harmful dinoflagellate, Cochiodinium polykrikoides. This study inspected a vertical migration of phytoplankton and Chl-a for reasonable sinking depth in floating cage. Furthermore, we analyzed the fluctuation of the phytoplankton including harmful dinoflagellates occurring in Yokgido for 6 years. Total cell density showed a significant monthly variation and the flora was predominated with diatoms. Gymnodinium sp. occurred 19 times, the greatest number of occurrence in all kinds of dinoflagellates during summer. In particular, the total number of occurrence at C. polykrikoides was 8, and harmful dinoflagellates such as Karenia brevis/Fibrcapsa japonica occurred. The relationship between Chl-a concentration/total cell number and sunset/sunrise was significant and reasonable sinking depth in floating cage was found to be at least 3m from the water surface, which was associated with massive fish kills caused by C. polykrikoides.

• Journal of Aquaculture
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• v.11 no.1
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• pp.39-48
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• 1998

Growth performance and excretions of nitrogen (N) and phosphorus (P) were investigated with carp (Cyprinus carpio) with carp (Cyprinus carpio) grower fed a low pollution diets (A and B) and commercial ones (Com-1 and Com-2). A recirculated rearing system (Exp. I) and a floating net cage system (Exp. II) were employed for two feeding trials in which fish having an initial body weight of 152g and 193g were fed for 41 an 39 days, respectively. The highest weight gain, daily growth rate and protein efficiency ratio were found (P<0.05) in fish fed diet A containing 10% fish meal and 2% monocalcium phosphate (MCP) for both experiments. They also showed the lowest feed conversion ratio and daily feeding ration among treatments. Fish fed diet B containing 10% fish meal, 5% fish protein concentrate and 1% MCP showed weight gain and FCR more improved (P<0.05) than those fed commercial diets. In all groups, whole body cmpositions were not greatly different among treatment, and protein and P contents in final fish ranged from 14.3 to 15.6% and from 0.39 to 0.48%, respectively. Fish fed diet A excreted the least N which were 38.3 in Exp. I and 39.6g/kg gain in Exp. II. However, the values found in fish fed two commercial diets amounted to 59.1 and 58.9g, respectively. A significant decrease in P excretion was also found in fish groups fed diets A and B. In Exp. I, a reduction of 53.4% was shown in fish fed diet A, compared to the averaged value (18.5g P/kg gain) of two commercial groups. In Exp. II conducted using the floating net cages, fish fed diet B excreted the least P (8.6g/kg gain) among the treatment, which was followed by fish fed diet A, showing 48.6% reduction compared to the average value (18.5g/kg gain) for fish fed two commercial diets. The present results clearly showed that N and P excretions from fish culture could be significantly reduced by using the low pollution diet.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.2 no.2
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• pp.151-159
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• 1997

Benthic respiration and chemical fluxes were measured at the sediment-water interface underlying the marine fish cages floating on the open coastal waters off Tong-Young, the South Coast of Korea. The effects of cage farming on coastal benthic environment and on mass balance of organic carbon in the benthic boundary layer under the marine fish cages are addressed. In a growing season of caged fishes of June, 1995, benthic chambers and sediment traps were deployed on the sediment-water interfaces of the two sites chosen for this study: 1) Cage Site, directly underlying the fish cages of the farm at 18 m water depth, and 2) Control Site, about 100 m away from the farm at 32 m water depth. Benthic respiration rates and chemical fluxes were calculated from the evolution of dissolved oxygen and chemicals in the chamber water, and mass balance of organic carbon in the benthic boundary layer was constructed based on the vertical flux of particulate organic matter (POM) and chemical fluxes out of the sediment. High organic dumping (6400 mg C $m^{-2}d^{-1}$) and high benthic respiration (230 mmol $O_2\;m^{-2}d^{-1}$) were observed at the Cage Site. Equivalent to 40% of vertical flux of organic carbon into the Cage Site seemed to be decomposed concurrently and released back to overlying waters (2400 mg C $m^{-2}d^{-1}$). Consequently, up to 4000 mg C $m^{-2}d^{-1}$ of organic carbon could be buried into the farm sediment (equivalent to 60% of organic carbon flux into the Cage Site). At the Control Site, relatively less input of organic carbon (4000 mg C $m^{-2}d^{-1}$) and low benthic respiration rate (75 mmol $O_2\;m^{-2}d^{-1}$) were observed despite short distance away from the cages. The influence of cage farming on benthic chemical fluxes might be restricted and concentrated in the sea bottom just below the fish cages in spite of massive organic dumping and high current regime around the fish cage farm.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.56 no.4
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• pp.473-483
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• 2023

This study was conducted to better understand the impact of marine fish farming by estimating mass balances of carbon and nitrogen. According to the results, 94.55% of carbon and 95.66% of nitrogen inputs were from the feed supplied in the farm. Of the total carbon emissions in the farm, 47.28% was due to fish respiration, which was subsequently released into seawater. Advection and diffusion in the farm contributed to 30.29% of the carbon released. In the case of nitrogen, 50.70% of the nitrogen released into the seawater was produced by fish excreta, and 31.37% was advected and diffused into the system. The sedimentary environment received 3.82% and 3.10% of the carbon and nitrogen released from the farm, respectively. The fish feed used for healthy growth contained 11.64% carbon and 9.17% nitrogen. Since the feed type was floating pellets, the load released into the sedimentary environment was relatively lower than that released into the marine environment. These findings suggest that the identification of an optimal fish feed that respects fish physiology and preserves a healthy ecology is critical for the future of aquaculture. Furthermore, ecosystem-based aquaculture systems that decrease environmental burden, while endeavoring to improve environmental health, are required.

• Journal of fish pathology
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• v.26 no.3
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• pp.173-183
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• 2013

From July to early September 2012, there was mass mortality of fishes, particularly black rockfish, which were being raised in the floating fish cage along the coast of Gyeongsangnam-do. The amount of damage was 1,802,000 fishes and the causes were confirmed to be rapidly rising water temperature and repeated daily changes in water temperature. The water temperature in this area of the sea rose to the maximum $28.4^{\circ}C$ and the daily range of changes in water temperature was maximum $6.5^{\circ}C$. As a result of investigating biological diseases of 194 fishes in 49 fishery areas, major pathogenic organisms such as red seabream iridovirus (RSIV), Vibrio sp. and Vibrio spp. or Microcotyle sp. were detected in rockfish in some fish farms. It is considered that the major causes of the mass mortality were high water temperature accompanied by repeated daily changes in water temperature, it is considered that biological diseases influenced the increase in the perish of fishes.