• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.9 no.2
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• pp.64-72
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• 2004

We measured the vertical profiles of $O_2$, H$_2$S, and pH in sediment pore water beneath marine cage fish farms using a microsensor with a 25 ${\mu}{\textrm}{m}$ sensor tip size. The sediments are characterized by high organic material load. The oxygen consumption, hydrogen sulfide oxidation, and sulfate reduction rates in the microzonations (derived from the vertical distribution of chemical species concentration) were estimated by adapting a simple one-dimensional diffusion-reaction model. The oxygen penetration depth was 0.75 mm. The oxic microzonations were divided into upper and lower layers. Due to hydrogen sulfide oxidation within the oxic zone, the oxygen consumption rate was higher in the lower layer. The total oxygen consumption rate integrated with reaction zone depth was estimated to be 0.092 $\mu$mol $O_2$cm$^{-2}$ hr$^{-1}$ . The total hydrogen sulfide oxidation rate occurring within 0.7 mm thickness was estimated to be 0.030 $\mu$mo1 H$_2$S cm$^{-2}$ hr$^{-1}$ , and its turnover time in the oxic sediment layer was estimated to be about 2 minutes. This suggests that hydrogen sulfide was oxidized by both chemical and microbial processes in this zone. The molar consumption ratio, calculated to be 0.84, indicates that either other electron accepters exit on hydrogen sulfide oxidation, or elemental sulfur precipitation occurs near the $O_2$- H$_2$S interface. Total sulfate reduction flux was estimated to be 0.029 $\mu$mol cm$^{-2}$ hr$^{-1}$ , which accounted for more than 60% of total $O_2$ consumption flux. This result implied that the degradation of organic matter in the anoxic layer was larger than in the oxic layer.

• Journal of fish pathology
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• v.11 no.2
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• pp.97-104
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• 1998

Since 1989, mass mortality has repeatly occurred in cage-cultured sevenband grouper, Epinephelus septemfasciatus along the southern coast of Korea in the summer season and usually reached over 80% within a few months. Diseased fish showed the clinical signs of anorexia, dark coloration, loss of eqilibrium, spinal swimming behaviour, vertebral deformity and inflation of swim bladder. Histopathologically, necrosis and/or vacuolation of the nerve cells in the brain and retina were observed. We previously reported that the causative agent was filtrable. The causative agent was not culturable in various fish cells; RTG-2, CHSE-214, BF-2, EPC and FHM. However, electron microscopic observation revealed unenveloped icosahedral viral particles with about 30 nm in diameter in the cytoplasm of nerve cells of the brain. The characteristics of the virus was tested by an artificial infection with the filtrate of the homogenate of diseased fish. The pathogenicity of the virus was retained after treatment with ether or heat ($50^{\circ}C$, 30 min) but partly lost by pH 3 or 11 treatment. These results suggest that the causative agent are similar to the fish nodavirus. In order to compare the causative agent with a fish nodavirus, Striped Jack Nervous Necrosis Virus (SJNNV), a polymerase chain reaction (PCR) was performed with primers specific to SJNNV. As a result, about 430 by PCR products were detected from the brain and the eye of both naturally and artificially infected sevenband grouper. All these results represent that the mass mortality in the cultured sevenband grouper is caused by the infection of a nodavirus similar to SJNNV and this is the first report of a fish nodavirus from the cultured sevenband grouper in Korea.

• 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.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.12 no.4
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• pp.287-304
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• 2007

This study was carried out to investigate spatio-temporal variations of benthic environment and macrobenthic polychaete communities in Gamak Bay where excessive organic matters from untreated sewage effluents and fish and shellfish farming activities have been accumulated in certain regions. Such environmental variables as sediment composition, organic content, acid volatile sulfide and dissolved oxygen content etc. were measured and polychaete specimens were taken in September 1999 and February 2000. In September 1999, organic contents were up to three times higher in the northwestern part of the bay and the area closed to Gukdong harbor than in the rest of the bay. In particular, benthic environment of the northwestern part of the bay was extremely deteriorated by the occurrence of hypoxia and highly concentrated sulfide. Of 28 stations investigated in summer, 5 stations located in the northwestern part were azoic. In the rest of the stations, a total of 119 polychaete species were sampled with a mean density of 900 $ind./m^2$. While species richness was higher in the entrance and central part of the bay where water exchanges with open sea were relatively active, density was higher in the moderately enriched stations neighbouring Gukdong harbor and fish farms where such potential indicators of organic pollution as Aphelochaeta monilaris, Lumbrineris longifolia were largely dominant. In February 2000, a total of 81 polychaete species appeared with a mean density of 2,802 $ind./m^2$ from 12 stations sampled in winter. Azoic areas were recolonized by Capitella capitata, Pseudopolydora paucibranchiata and Dipolydora socialis which showed maximum density in the innermost station. On the other hand, the rest of the stations were dominated by Euchone alicaudata and Praxillella affinis. The configuration of the stations sampled in summer and winter on the multidimensional scaling plots reflected the position of each stations within the bay in which there were great differences in organic content, sulfide concentration and oxygen content rather than in sediment composition. Therefore, heterogeneities in polychaete community structure in Gamak Bay were primarily influenced by the degree of the disturbance depending on the position within the bay.