• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.3
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• pp.296-301
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• 2017

We conducted a study to 1) determine the indicators of gonadal maturity in male and female Korean walleye pollock Theragra chalcogramma for the purposes of artificial insemination; 2) establish the RNA/DNA ratio of mature eggs in this species; and 3) monitor the effect of refrigerated storage on egg viability and the motility of sperm collected from dead adult males. During the spawning season, the color of female gonads changed from orange to transparent, and that of male gonads changed from pale orange to milky white. The DNA content and RNA/DNA ratio of mature eggs were maintained without significant changes for approximately 6 h when eggs were preserved at $4^{\circ}C$. Sperm could be obtained from both milt and undiluted semen. Sperm obtained from milt ceased moving on the second day after isolation, while over 60% of sperm obtained from semen showed movement until the 13th day. Seven attempts were made to artificially inseminate mature eggs, of which two resulted in successful fertilization. The successful inseminations produced 94,000 and 5,000 fertilized eggs, respectively. This study shows that artificial insemination of walleye pollock is a viable strategy when natural propagation is not possible.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.49 no.3
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• pp.359-366
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• 2016

The health of Alaska pollock Theragra chalcogramma seedlings was monitored during February and April 2015. After microscopic examination for parasites, 20 samples sets were made by pooling 50 individuals for each sample set. Then, they were homogenized and examined for viral and bacterial pathogens. No parasites or viruses were detected using either microscopy or PCR. Colonies suspected of belonging to the genus Vibrio were isolated from Tryptic Soya Agar and Thiosulfate Citrate Bile Salts Sucrose Agar plate incubations, and identified as Vibrio anguillarum based on biochemical and physiological examinations and PCR amplification of the 16S rDNA, recA, and pyrH genes. Although there was no mortality during the sampling period, 65.0% (13/20) of the pooled samples were PCR-positive for V. anguillarum. To prevent possible outbreaks, the pathogenic potential of V. anguillarum should be investigated in the future.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.48 no.3
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• pp.293-300
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• 2015

We sought to extend the shelf-life of Alaska pollack Theragra chalcogramma sikhae while maintaining quality. We compared the chemical, microbiological, and organoleptic characteristics of sikhae prepared under four different conditions. Control fish were fermented at ambient temperature ($21{\pm}2^{\circ}C$); other samples were stored at $5^{\circ}C$ after fermentation at ambient temperature for 36 h (A1), 60 h (A2), and 84 h (A3). Volatile basic nitrogen and amino-nitrogen levels, and total acidity increased with fermentation time in all samples, but the pH fell, attaining a relatively lower level in the control than in other samples. Over 90% of all viable cells were lactic acid-producing bacteria; this proportion did not change significantly during fermentation. In terms of texture, only hardness was affected by fermentation. The hardness of the control fell more rapidly than did that of the other samples. In terms of sensory evaluation (the acceptance test and quantitative descriptive analysis [QDA]), A2 was superior to other samples after fermentation for different times; A2 maintained limited salability (6 points on the relevant index) for up to 17 days of storage.

• Parasites, Hosts and Diseases
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• v.30 no.4
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• pp.255-258
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• 1992

Two fully matured specimens were collected from the blood vessel of two fish, Tlreragra chatcogramma, which was bought at the Emun market of Seoul in May, 1985. The blood cuke has no pharynx and suckers. Its body surface was covered with minute spines forming fan-shaped groups, 15 Mm long. The intestine was H-shaped, and the ratio of esophageal length to body length was 1 : 6.1∼6.8. Irregular shaped testes were 109∼114 in number, occupying the intercecal space from cecal bifurcation to the genital pore. The present species was identified as Aporocotyle sheragrae. This is the first report of the species in Korea.

• Korean Journal of Pharmacognosy
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• v.25 no.1
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• pp.76-77
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• 1994

Contents of nucleic acid metabolites, such as uracil, uridine and hypoxanthine in the unossified pilose antler of Cervus nippon Temminck var. mantchuricus Swinhoe and the frozen and dried meat of Theragra chalcogramma (Thallas) were determined by high-performance liquid chromatography. The amount of hypoxanthine in the water extract of the meat (39.2 mg %) was higher than that of the antler (24.6 mg %).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.549-555
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• 2018

The objectives of this study were to confirm the nutritional requirements and improve the survival of the walleye pollock Theragra chalcogramma, a cold seawater fish, by enrichment. We analyzed the fatty acids and amino acids of fertilized pollock eggs before hatching, just-hatched larvae, larvae that had absorbed only the yolk sac, and larvae starved for 2 days after yolk absorption. For the survival improvement experiment, we administered docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and DHA-EPA enrichment. Fatty acid decreased DHA and EPA content. On the $30^{th}$ day, body growth was significantly greater in pollock given the EPA and DHA-EPA treatments (P<0.05). Larval survival at 20 and 30 days after hatching (DAH) was greatest under the DHA-EPA treatment (P<0.05). Survival was significantly lower under the EPA treatment at 10 DAH, but then increased to approach that seen under the EPA-DHA treatment (P<0.05). Therefore, we determined that reduced survival in hatchlings of high-mortality pollack could be improved by controlling EPA and DHA content during enrichment. We conclude that cold seawater fish must be given feed that meets their nutritional needs, which can be accomplished using newly manufactured enrichment products for the larvae of cold seawater fish, such as pollock.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.2
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• pp.83-88
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• 2005

Protease inhibitors were purified from the eggs of Alaska pollock (Theragra chalcogramma) using the following purification steps: ammonium sulfate precipitation, ion exchange, gel permeation, and high performance liquid chromatographies (HPLC). The protease inhibitor from the heated eggs of Alaska pollock was not as well purified. In addition, the heated eggs showed lower specific inhibitory activity than the unheated eggs. The purification yields after ammonium sulfate precipitation, ion exchange, and gel permeation chromatographies were 22.7$\%,\;15.3\%$,and $4.4\%$, respectively. There were two kinds of protease inhibitors on the gel permeation chromatography pattern Their molecular weights were estimated to be 66,700 and 16,000 Da, respectively. Both were classified as a cysteine protease inhibitor because of the existence of inhibiting papain, which is one of cysteine proteases.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.5
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• pp.437-441
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• 2003

This research investigated the effects of processing conditions and natural antimicrobial materials on quality of freeze-dried, seasoned and roasted Alaska pollack (Theragra chalcogramma). The optimum dipping time and moisture contents of freeze-dried Alaska pollack were 1 sec in $1\%$ salt solution, $48.6\%$ respectively. The freeze-dried, seasoned and roasted Alaska pollack product showed high sensory value. As sterilization time increased over 30 mins in water bath at $100^{\circ}C$ the browning degree of the freeze-dried, seasoned and roasted Alaska pollack product increased. Among various antibrowning agents, $3\%$ corn starch was better in preventing browning than sporix treatment. The freeze-dried, seasoned and roasted Alaska pollack product added with lactate Ca and catechin had the antimicrobial, and the VBN contents of the product showed low level.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.52 no.2
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• pp.105-113
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• 2019

The objective of this study was to investigate Alaska pollock Theragra chalcogramma roe grade distribution among blocks and its nutritional components by grade. M grade roe was predominantly distributed in blocks labeled as L and M (52.1 and 82.8%, respectively), and S grade roe was mainly found in blocks labeled as S (98.6%). Products labeled as containing KB and KC grade roe contained 77.1 and 65.5% normal roe, respectively. Among the five roe grades (L, M, S, G, and Off), total amino acid content was higher in normal roe than in abnormal roe. The major amino acids found in normal roe were leucine, aspartic acid, and glutamic acid, whereas G and Off grade roe contained leucine and glutamic acid, but not aspartic acid. The calcium, phosphorus, potassium, and iron contents of the five roe grades were within the ranges 13.0-20.0, 314.4-392.0, 124.1-157.7, and 1.7-2.2 mg/100 g, respectively. The five roe grades contained total fatty acid contents of 765-1,252 mg/100 g, with no significant differences among grades. The major fatty acids were 16:0, 18:1n-9, 20:5n-3, and 22:6n-3.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.6
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• pp.948-953
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• 2021

To find the optimal eggs to larvae transforming temperature of walleye pollock Theragra chalcogramma, we investigated their hatching pattern, mortality, and larval deformities. Results showed that the hatching quality decreased as the water temperature increased and dropped sharply above 13℃. The highest hatching rate was achieved at 7℃, whereas the lowest was at 15℃. Dead eggs were not observed at 7℃; however, dead egg ratios were significantly high at 4.5℃ and above 13℃ (P<0.05). Mortality of larvae after hatching was not observed at 4.5℃, but was significantly high above 13℃. The DNA content of the larvae did not show any significant difference at all water temperatures; however, RNA content was the highest at 7℃ and was significantly low above 11℃. In addition, RNA/DNA ratio was the highest at 7℃. Larval deformities after hatching were low at 7-11℃ and higher at higher or lower water temperature. Therefore, the hatching index and larval health index of Walleye pollock eggs in this study show that 7℃ to 11℃ seems to be the optimal transforming water temperature range.