• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.4
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• pp.235-246
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• 2002

The fish farming using net cages has been developed in many semi-closed bays in the southern coast of Korea for the last two decades. The intensive cage cultures of fishes generate considerable amounts of organic waste in the form of uneaten food and faeces. In order to evaluate the effect of fish farming activities we collected the benthic macrofauna near the fish farm area located in Wolho Islet of Gamak Bay and in Haklim Island of Tongyeong in November 1998. Benthic macrofaunal assemblages showed dramatic changes in species number, species diversity, and faunal abundance in the region of the fish farm. These changes were clearly observed even at a distance of up to 30 m from the fish farming cage area. Within 5 m from the cage, there was a zone with low species diversity and highest density, dominated by opportunistic polychaete worm, Capitella capitata. By a distance of 15-30 m, this zone presents highest species number and higher density. Our results clearly demonstrated that fish farm area was highly enriched with organic materials, and implied that the fish farm industry and adjacent benthic ecosystem in semi-closed bay will be seriously damaged by self produced organic wastes in the near future.

• Journal of fish pathology
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• v.13 no.2
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• pp.121-127
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• 2000

From August to October 1998, over 60% mortality of cultured striped beakperch Oplegnathus fasciatus was occurred in net cages along the southern coast of Korea. Moribund fish showed some clinical signs of lethargic behavior, dark coloration or decoloration, severe gill anemia and enlargement of spleen. Also enlarged basophilic cells showing Feulgen -positive reaction were observed in the tissue section of spleen, kidney, liver and heart of the diseased fish. GF cells inoculated with spleen homogenate of diseased fish produced cytopathic effect of enlarged and rounded cells, therefore the causative virus was isolated from diseased fish. Striped beakperch fingerlings intraperitoneally inoculated with the causative virus ($10^4TCID_{50}$/0.1 ml) revealed symptoms similar to those of naturally infected fish and died from 7 to 14 days post injection. Transmission electron microscopy revealed that the causative virus was enveloped icosahedral particle with 120~130 nm in diameter. PCR products of the expected size (500 bp) were amplified with a primer set based on the ATPase gene of RSIV(red sea bream iridovirus) using template DNAs which were extracted from the spleen of diseased fish and GF cells inoculated with the causative virus. According to the analysis of nucleotide sequence of these PCR products, the sequence from ATPase cDNA gene of the causative virus showed 95% homology with that of RSIV. These results indicate that the mass mortality in the cultured striped beakperch was caused by the infection of iridovirus similar to RSIV.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.1
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• pp.43-50
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• 2001

In order to analyze the dynamic motions of fish cage systems made of a frame and a netting under the conditions of waves and current, the hydraulic model experiment at towing tank and the numerical computation using boundary integral element method based on linear potential theory were carried out on a square and a circular type of fish cage, The computed and measured results for the dynamic motions of model fish cage systems showed that the heave and pitch motions were almost unaffected by the inclusion of nets, while the surge motions were very reduced by drag force acting on them. In addition, irregular wave-induced motions of fish cages included non-negligible 2nd order harmonic components at high frequency nearly twice the wave frequency. The reason why these motions were considered was due to resonance or structural components of frames being overflown and out of water during a wave cycle. It was found that circular type was more desirable structure in the open sea than square one only in the respect of dynamic motions due to waves and current. Further verifications were needed considering hydrodynamic forces, fatigue life, and structure analysis based on long term stochastic waves including frequency and time domain for the purpose of analyzing and designing fish cage systems.

• Ocean Systems Engineering
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• v.7 no.2
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• pp.143-155
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• 2017

For complex flexible structures such as nets, the determination of drag forces and its deformation is a challenging task. The accurate prediction of loads on cages is one of the key steps in designing fish farm facilities. The basic physics with a simple cage, can be addressed by the use of experimental studies. However, to design more complex cage system for various environmental conditions, a reliable numerical simulation tool is essential. In this work, the current load on a cage is calculated using a Morison-force model applied at instantaneous positions of equivalent-net modeling. Variations of solidity ratio ($S_n$) of the net and current speed are considered. An equivalent array of cylinders is built to represent the physical netting. Based on the systematic comparisons between the published experimental data for Raschel nets and the current numerical simulations, carried out using the commercial software OrcaFlex, a new formulation for $C_d$ values, used in the equivalent-net model, is presented. The similar approach can also be applied to other netting materials following the same procedure. In case of high solidity ratio and current speed, the hybrid model defines $C_d$ as a function of Re (Reynolds number) and $S_n$ to better represent the corresponding weak diffraction effects. Otherwise, the conventional $C_d$ values depending only on Re can be used with including shielding effects for downstream elements. This new methodology significantly improves the agreement between numerical and experimental data.

• Proceedings of the Korean Aquaculture Society Conference
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• 2003.10a
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• pp.37-37
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• 2003

Intraspecific hybrids have been proven to be a useful tool for increase growth rate in some freshwater fish species. However the effects of intraspecific hybrids in seawater fish species is little known. To assess whether intraspecific hybrids in red sea bream was associated with growth enhancement, growth performances of offspring from two inbred lines, selected Korean line (KORDI-F4) and cultured Japanese line (IPN) and two intraspecific hybrids lines (KORDI-F4♀×JPN♂ and JPN♀×KORDI-F4♂) of red sea bream were compared. There's no significant difference in body weight between offspring groups during seed production period (until 4 months old). At seven months old (after three months rearing trials on sea cages communally), the offspring from KORDI-F4 (41.0±11.1g) and JPN♀×KORDI-F4♂ (39.3±8.1g) showed significantly better performance in body weight than that of the offspring from KORDI-F4♀×JPN♂ (37.0±8.1g) and IPN (35.7±9.7g). At 15 months old, the offspring from JPN♀×KORDI-F4♂ showed best growth performances in body weight, weight gain, specific growth rate among four offspring groups. As the results, the intraspecific hybrids between cultured Japanese line and selected Korean line showed superior growth performances than their paternal and maternal inbred lines.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.3
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• pp.432-442
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• 2020

Diagnostic monitoring in Korean rockfish cages was performed to survey the prevalence of pathogens in cultured Korean rockfish Sebastes schlegeli from May 2013 to July 2016. A total of 1,945 fish samples collected from the western (Cheonsu Bay and Heuksando), southern (Tongyeong and Namhae), and eastern coasts (Pohang) of Korea were tested for parasites, viruses, and bacteria. In this study, 1,264 and 334 fishes were infected with Microcotyle sebastis and Clavinema mariae, respectively. The prevalence rates of C. clavinema in fishes from Cheonsu Bay, Heuksando, and Tongyeong were 35.3%, 3.9% and 1.9%, respectively. No C. clavinema infection was detected in cultured rockfish from Namhae and Pohang. Furthermore, bacteria including Photobacterium damselae (8.9%), Photobacterium piscicola (2.3%), Photobacterium spp. (8.9%), Aeromonas salmonicida (1.8%), Aeromonas spp. (0.9%), Vibrio scophthalmi (1.5%), Vibrio spp. (3.3%), Streptococcus iniae (1.2%), and others (8.0%) were detected in 373 of 1,364 fishes. No virus was detected in any fish investigated in this study.

• Proceedings of the Korean Aquaculture Society Conference
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• 2003.10a
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• pp.36-36
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• 2003

In the present study, growth performances of the offspring from selected brood line were compared to those of the offspring from non-selected brood line of red sea bream. Offspring groups were mass produced separately from two brood lines, selected and non-selected Korean strain. Selected brood line have been selected by fish size for four generations (upper 5∼30% per generation) and non-selected brood line is the second generation of wild population at south sea in Korea. There's no significant difference in body length between offspring from selected and non-selected brood line during early growing stage (until 96-days old). However, offspring from selected brood line had superior body weight growth than offspring from non-selected brood line. At sea cages rearing trials with communal stocking, Offspring from selected brood line showed significantly better performance in body weight, body length, weight gain, specific growth rate and feed consumption (but not in feed conversion ratio) than offspring from non-selected brood line. At 24 months old, offspring from selected brood line grew faster 1.10 times in body length and 1.41 times in body weight than offspring from non selected brood line. The response to selection when compared to a non-selected line is on average of 10% in weight per generation at 24 months old.

• International Journal of Industrial Entomology and Biomaterials
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• v.33 no.2
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• pp.92-95
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• 2016

The black soldier fly is economically important because its prepupae are used as feed for many animals, including fish and swine. In Korea, black-soldier-fly farms have attempted to increase annual breeding and mass egg production for use in animal feed, as well as the decomposition of organic waste. Such efforts require an understanding of optimal mating and oviposition techniques. Specifically, adult densities and cage size may both improve the efficiency of mass egg production. Our study used four sizes of nylon cages ($1.0{\times}1.0{\times}2.5m$, $1.5{\times}1.5{\times}2.5m$, $2.0{\times}2.0{\times}2.5m$, $2.5{\times}2.5{\times}2.5m$) and three density treatments (4 kg, 8 kg, and 10 kg of pupae) to investigate optimal habitat size and adult density. We found that cage size (independent of density) did not significantly influence female fecundity (number of egg clutches and egg weight), whereas higher densities increased egg number and weight regardless of cage size. Thus, we recommend manipulating adult density to enhance productivity in commercial black-soldier-fly farming. However, we also propose further detailed research to develop methods that account for seasonal changes and environmental conditions, as climatic variables (temperature, sunlight) likely influence female fecundity as well.

• Ocean and Polar Research
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• v.43 no.4
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• pp.255-267
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• 2021

To understand the composition and community changes of benthic species by water depth (5 m, 20 m, 30 m) in the cage facilities, net substrate made of fish cages were installed at intervals of 2 months from March to September 2019, which is the main period of sessile organism recruitment. Water temperature and salinity varied in the ranges of 1~5℃ and 1~4 mg/L at 5 m from June to August, respectively, and less difference was observed according to water depth in other investigation periods. A total of 37 benthic animals were recruited, and Kamptozoa unid., Caprella scaura and Jassa slatteryi were verified during the entire study period. Mytilus galloprovincialis, a Mediterranean mussel, showed seasonality dominant only from spring to early summer (March to July). The community structure classified by temporal and spatial factors, and Bugula neritina, Kamptozoa unid., and Sertularella sp. contributed to the formation of the community. The depth of 5 m was exposed to environmental changes in water temperature and salinity temporally, so there was a seasonal variation in the composition of the sessile organism, but at depths of 20 m and 30 m, there was less significant environmental change and it showed relatively stable than 5 m.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.6
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• pp.731-737
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• 2016

To understand the characteristics and strength of the cold water that has caused damage to marine-culturing farms around Guryongpo, in the southwestern part of Korea, surface and water column temperatures were collected from temperature loggers deployed at a sea squirt farm during August-November 2007 and from a Real-time Information System for Aquaculture environment operated by NIFS (National Institute of Fisheries Science) during July-August 2015 and 2016. During the study period, surface temperature at Guryongpo decreased sharply when south/southwestern winds prevailed (the 18-26th of August and 20-22nd of September 2007 and the 13-15th of July 2015) as a result of upwelling. However, the deep-water (20-30m) temperature increased during periods of strong north/northeasterly winds (the 5-7th and 16-18th of September 2007) as a result of downwelling. Among the cold water events that occurred at Guryongpo, the mass death of cultured fish followed strong cold water events (surface temperatures below $10^{\circ}C$) that were caused by more than two days of successive south/southeastern winds with maximum speeds higher than 5 m/s. A Cold Water Index (CWI) was defined and calculated using maximum wind speed and direction as measured daily at Pohang Meteorological Observatory. When the average CWI over two days ($CWI_{2d}$) was higher than 100, mass fish mortality occurred. The four-day average CWI ($CWI_{4d}$) showed a high negative correlation with surface temperature from July-August in the Guryongpo area ($R^2=0.5$), suggesting that CWI is a good index for predicting strong cold water events and massive mortality. In October 2007, the sea temperature at a depth of 30 m showed a high fluctuation that ranged from $7-23^{\circ}C$, with frequency and spectrum coinciding with tidal levels at Ulsan, affected by the North Korean Cold Current. If temperature variations at the depth of fish cages also regularly fluctuate within this range, damage may be caused to the Guryongpo fish industry. More studies are needed to focus on this phenomenon.