• Korean Journal of Ichthyology
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• v.34 no.2
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• pp.102-112
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• 2022

This study investigated dietary habits and intra- and inter-specific food resource partitioning of co-occurring walleye pollock (Gadus chalcogrammus) and Pacific cod (G. macrocephalus) from the waters off the north-eastern coast of South Korea using stomach contents and stable isotopes (δ¹³C and δ¹⁵N) analyses. Both species are mesopelagic carnivores that consumed mainly benthopelagic crustaceans, but teleosts were also abundant in the diet of Pacific cod. Non-metric multidimensional scaling (nMDS) ordination and permutational multivariate analysis of variance (PERMANOVA) of dietary data revealed significant intra- and inter-specific dietary differences, i.e., food resource partitioning. Nitrogen stable isotope values (δ¹⁵N) were similar between walleye pollock and Pacific cod, but carbon stable isotope values (δ¹³C) were significant different, suggesting different trophic positioning. Canonical analysis of principal coordinate (CAP) ordination plot further demonstrated that differences in the type and range of prey ingested by the two species contributed such an inter-specific difference in the diet compositions. Ontogenetic changes in diet compositions were evident. As walleye pollock, they preyed more upon carid shrimps and cephalopods, but no such trend was observed in the diets of Pacific cod. While stable isotope values indicated that large-sized specimens of both species were significantly enriched in ¹⁵N relative to smaller conspecifics thus supporting these data. Consequently, in this study, both methodologies, i.e., stomach contents and stable isotope analyses, provided evidence of inter- and/or intra-specific dietary segregations and trophic niche partitioning between co-occurring walleye pollock and Pacific cod off eastern Korean waters.

• Journal of fish pathology
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• v.30 no.1
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• pp.1-9
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• 2017

This study was conducted to monitor the prevalence of viral hemorrhagic septicemia virus (VHSV), nervous necrosis virus (NNV) and marine birnavirus (MABV) in cultured walleye pollock Gadus chalcogrammus by RT-PCR. All of the viruses tested were not detected by one-step PCR in 62 spleen sample sets, except for NNV in one brain sample set (1/55). By two-step PCR, VHSV was detected in 51.6%(32/62) and NNV was detected in 1.6%(1/62) spleen sample set, but MABV was not detected. In the brain sample sets, the detection rate of NNV was 3.6%(2/55). VHSV and NNV were detected for the first time in cultured walleye pollock in this study. However, the titers of viruses in these sample sets are thought to be very low, because most of the positive sample sets were detected by two-step PCR and none of the fish showed any clinical symptoms of each virus. Continuous monitoring, subsequent virus isolation and validation of carrier fish will be necessary.

• Korean Journal of Ichthyology
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• v.32 no.2
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• pp.78-83
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• 2020

This study aimed to investigate the effects of different water temperature (5, 8 and 11℃) on egg hatch and larval growth of walleye pollock Gadus chalcogrammus to improve rearing techniques for this species. Survival of eggs maintained at 5℃ was higher than that of eggs maintained at 8℃ and 11℃. The greatest hatching rate was obtained for larvae maintained at 8℃. However, time to first, 50% and 100% hatch of eggs maintained at 11℃ was shorter than at 5℃ and 8℃. A higher survival was observed in larvae reared at 5℃ compared to 8℃ and 11℃ and the greatest growth was observed in larvae reared at 11℃ compared to 5℃ and 8℃ during the feeding trial. This study demonstrated the importance of water temperature, as it affects culture performance of eggs and larval pollock. The results from this study provides valuable information for further development of pollock aquaculture.

• Korean Journal of Ichthyology
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• v.29 no.1
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• pp.62-68
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• 2017

The Alaska pollock (Gadus chalcogrammus) belongs to the family Gadidae; it is a cold water fish, and has been developed as a novel aquaculture species in Korea. In this study, we describe ongoing surveillance for aquatic animal pathogens based on growth stages. We investigated bacterial flora in rearing water, and monitored pathogens; we also analyzed histopathological traits of abnormal fish. In rearing water, the total bacterial counts were $2.1{\times}10^3cfu/mL$ and Vibrio spp. (52%) were predominant in the larvae stage. In the juvenile and adult stages, the total bacterial counts were $3.4{\times}10^3$ and $3.2{\times}10^2cfu/mL$, respectively (with Pseudomonas sp. as the predominant species; 90% and 52%). This result revealed that the bacterial flora in rearing water changed depending on the feeding types. No virulent-bacteria or problematic viruses (VHSV, viral hemorrhagic septicemia virus; NNV, nervous necrosis virus; MBV, marine birnavirus) were detected from outwardly healthy fish using either culture or PCR assay. Some juveniles (less than 5%) had gas bubbles on the gill lamellae, degeneration of the corneal epithelium, and choroid gland degeneration, suggesting that these symptoms were caused by external injury and secondary infection by opportunistic bacteria. Disease management is important to cope with disease emergence in the novel aquaculture species Alaska pollock.

• Korean Journal of Ichthyology
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• v.32 no.3
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• pp.148-159
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• 2020

This study investigated the seasonal and inter-annual changes in vertical distribution and size spectrum of walleye pollock, Gadus chalcogrammus inhabiting middle eastern coast of Korea (hear after pollock). Pollock was distributed between 50 m and 600 m depth range, and body size (total length) ranged from 16.6 cm to 81.5 cm. The trends of population body size were increased in autumn and winter and decreased in spring and summer. Vertical distribution of pollock showned depth-dependent patterns with distributing smaller individuals mainly in the upper layer (shallower depth), while larger fish in deeper habitats. Those patterns in vertical distribution of pollock population is probably due to be the results of energy-saving strategy, metabolic effects, and changes in prey selections according to pollock growth, derived from spatial and temporal changes in oceanic condition in habitat grounds. When water temperature in upper layer were increased and that of below thermocline depth became decreased in 2017, the ratio of smaller (<35 cm) and larger (≥35 cm) individuals was biased toward larger fishes, extending their distribution into shallow depth, and consequently main fishing ground was formed in far from coastal area. In addition, the ratio of smaller individual distributing between 100~300 m was increased with decreasing temperature gradient between below thermocline and bottom layer. Changes in spatial and temporal distributions of pollock population likely be related with vertical and horizontal changes in oceanic conditions and, consequently food supplies.

• Journal of Environmental Health Sciences
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• v.44 no.3
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• pp.259-266
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• 2018

Objectives: Considered the "national fish" in Korea, the walleye pollock (Gadus chalcogrammus) has disappeared in the East Sea (Sea of Japan), a main habitat and fishing ground for the species. The reason for the disappearance is still a matter of controversy. This study was performed to investigate the long-term relationship between the walleye pollock catch and various meteorological and oceanographic factors in these waters. Methods: Fishery data on walleye pollock and data on meteorological and marine environmental factors over the 30 years (1981-2010) were obtained from the official national database. Time series analysis and correlation and regression analyses were performed to study the relationships. Results: Both air temperature and sea surface temperature in the East Sea rose over these 30 years, and the latter became more prominent. Salinity and dissolved oxygen showed a tendency to decrease while concentrations of nutrients such as nitrite nitrogen and nitrate nitrogen showed an increasing tendency. Sea surface temperature, air temperature, atmospheric pressure, and wind grade were negatively correlated with the catch size of walleye pollock (p<0.05), but salinity was positively correlated (p<0.001). Conclusion: The results of this study indicate that climate change, especially ocean warming, affected the habitat of walleye pollock. The results also indicate that lower sea surface and air temperatures, milder wind grade, and higher salinity were preferred for the survival of the fish species. It is necessary to pay attention to changes of the ocean ecosystem in terms of environmental pollution as well as seawater temperature.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.3
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• pp.297-307
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• 2020

This study investigated the cosmetic effects of enzymatic hydrolytes of an aquatic by-product, fish skin. The skins of olive flounder Paralichthys olivaceus (PO) and Alaska pollock Gadus chalcogrammus (AP) were hydrolyzed using pepsin, Alcalase, and Protemax. Three enzymatic hydrolytes were obtained and the inhibitory effects of these hydrolytes on the aging-related enzymes tyrosinase, elastase, and collagenase were determined. The results indicated that the pepsin hydrolytes of PO and PA had stronger activities than the other hydrolytes. PO and PA also significantly reduced the intracellular reactive oxygen species levels in and improved the viability of H₂O₂-treated Vero cells; decreased nitric oxide production by and increased the cell viability of lipopolysaccharide-treated RAW 264.7 cells; and reduced intracellular reactive oxygen species levels and improved the viability of ultraviolet B irradiated HaCaT cells and human dermal fibroblasts. Furthermore, PO and PA remarkably reduced the intra- and extracellular melanin contents of alpha-melanocyte-stimulating hormone-stimulated B16F10 cells. These results demonstrate that PO and PA have potential for use in the cosmetic industry.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.2
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• pp.195-205
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• 2020

Oceanic conditions in walleye pollock habitat in the East Sea have shown decadal fluctuations between warm and cold periods in turn. Specifically, sea surface temperature (SST) has shown a dramatic increase between the late 1980s and the middle 2000s, and abrupt decreasing patterns after the late 2000s. Oceanic conditions in the Dong-han Bay (spawning ground) and middle eastern coastal waters (fishing ground), however, indicated different fluctuation trends in SST, increasing in the Dong-han Bay after the late 1980s, and decreasing after the late 2000s. These fluctuation patterns were especially clear in February and March. Sea surface temperature in the middle eastern coastal waters of Korea soared continuously after the late 1980s, but did not show a distinct decreasing pattern after the late 2000s compared with Dong han Bay, except for February SST values. These long term water temperature changes in both walleye pollock spawning and fishing ground are related to variation in walleye pollock landings. Especially, abrupt changes in spawning ground SST can be one of the factors influencing survival in the early ontogenesis of walleye pollock, including egg and yolk larval stages. During the 1980s, the area of suitable spawning temperature (2-5℃) was wider, and the length of Walleye pollock egg and larval stages greater compared with past and present oceanographic environments. However, such patterns did not correspond with the optimal spawning temperature range and greater length of development of walleye pollock during the late 1980s likely triggering a decline in pollock stock. In conclusion, it has been supposed that the dramatic decrease in walleye pollock landings in the East Sea since the late 1980s was caused by increasing water temperature leading to both early mortality and unsuitable spawning conditions.

• Journal of Life Science
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• v.29 no.4
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• pp.428-435
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• 2019

Alaska pollock (Gadus chalcogrammus) is a marine fish species belonging to the family Gadidae. In this study, whether the Alaska Polloack Roe have antioxidant properties, 2,2-diphenyl-1 picrylhydroazyl (DPPH), hydroxyl radical (OH) reducing activity, and nitric oxide radical (NO) scavenging activity were evaluated in distilled water extract (DWE) and ethanol extract (ETE) of raw Alaska pollock roe, Gochujang Pollock roe, and fermented seasoned Pollock roe. The DPPH scavenging activity of the DWE with Gochujang Pollock roe was 71.9% at a concentration of 1.0 mg/ml and that of the ETE was 73.7% at the same concentration. The DPPH scavenging activity of the DWE with fermented seasoned Pollock roe was 78.0% at 1.0 mg/ml, whereas that of ETE was 78.4% at the same concentration. The $IC_{50}$ values of the DWE and ETE of raw Pollock roe for DPPH were $11.65{\mu}g/ml$ and $11.47{\mu}g/ml$, respectively. The OH scavenging activities of raw Pollock roe, Gochujang Pollock roe, and fermented seasoned Pollock roe ethanolic extracts at a concentration of 1.0 mg/ml were 70.9%, 79.0, and 80.6%, respectively. The $IC_{50}$ values of the DWE and EWE of raw Pollock roe for NO were $11.45{\mu}g/ml$ and $11.41{\mu}g/ml$, respectively. The DPPH, OH, and NO scavenging abilities in DWEs and ETEs of Gochujang and fermented seasoned Pollock roe were higher than those of instant (no Gochujang or season treatment) treatment Pollock roe. Both the Gochujang and fermented seasoned Pollock roes have natural radical scavenging ability and may be useful potential antioxidant food supplements.

• Journal of Life Science
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• v.28 no.12
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• pp.1461-1468
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• 2018

The Alaska Pollock (Gadus chalcogrammus) is distributed in an arc across the North Pacific Ocean. Distilled water extracts (DWE) and ethanol extracts (ETE) of 1.0 mg/ml concentrations of raw Alaska Pollock roe, premium Gochujang Pollock roe, and premium fermented Pollock roe seasoning were evaluated for estimated 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), ferric reducing antioxidant potential (FRAP), and total phenolic content. The ABTS scavenging activity of the raw Alaska roe DWE and ETE were evaluated at 50.1% and 53.1%, respectively. The ABTS scavenging activity of the Gochujang roe DWE was 68.7% and of the ETE was 70.4%; for the fermented seasoning it was 71.3% and 71.6% for the DWE and ETE, respectively. The ABTS $EC_{50}$ values of the raw roe DWE and ETE were 12.49 ug/ml and 12.21 ug/ml, respectively. The FRAP $EC_{50}$ values of the Gochujang roe DWE and ETE were 10.67 ug/ml and 10.56 ug/ml, respectively, and the $EC_{50}$ values for total phenolic content for the fermented seasoning DWE and ETE were 10.45 ug/ml and 10.31 ug/ml, respectively. When Gallic was acid used as a control, the relative total phenolic content scavenging activity in each ETE was 52.0% (raw Alaska roe), 61.1% (Gochujang roe), and 63.6% (fermented seasoning). In the present study, higher ABTS, FRAP, and total phenolic content were observed in the Gochujang Pollock roe and fermented roe seasoning than in the Alaska Pollock roe.