• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.53 no.3
• /
• pp.456-463
• /
• 2020

The diet of the walleye pollock Gadus chalcogrammus, was studied by examining the stomach contents of 864 individuals. Using gill nets, samples were collected monthly from January to December 2017 in Jugwang, Sokcho, Yangyang, Uljin, Ganggu, and Gampo, Korea. The specimens ranged in total length (TL) from 16.6 to 75.2 cm. G. chalcogrammus fed mainly on Euphausia pacifica (Euphausiacea) and less on Cephalopoda, Pisces, Mysidacea, and Macrura. The results indicated that G. chalcogrammus is a specialist feeder, feeding mainly Euphausiacea. With growth, however, its diet shifted from Euphausiacea to Cephalopoda, Macrura and Pisces. Smaller individuals (<40.0 cm TL) consumed mainly Euphausiacea. The proportion of Euphausiacea decreased with increasing body size, whereas the consumption of Cephalopoda and Macrura increased gradually.

• Korean Journal of Ichthyology
• /
• v.31 no.3
• /
• pp.141-149
• /
• 2019

This study presents data on spawning season, weight-length relationships (WLRs) and condition factor of Gadus chalcogrammus inhabiting the middle East Sea, Korea. Monthly changes in the gonadosomatic index (GSI) revealed that the spawning period was from December to March. Overall value of the exponent b, estimated by nonlinear least squares from weight and length data was 2.806, ranging from 2.778 for female fishes to 2.985 for immature group. The b values were similar between spawning and non-spawning, and between female and male fishes, but it was significantly higher for immature than mature fishes. The condition factors were significantly higher for immature than mature groups, and during non-spawning than spawning periods, but it was not significant between male and female fishes.

• Journal of Environmental Science International
• /
• v.29 no.6
• /
• pp.633-641
• /
• 2020

Water temperature is one of the most important factors of fish survival, affecting the habitat, migration route, development, and reproduction. This experiment studied the induction level of heat shock protein (HSP70) mRNA and protein in a walleye pollock (Gadus chalcogrammus) primary hepatocyte culture based on different temperatures. Hepatocytes were attached at 7.5℃ for 24 hours. Hsp70 induction levels were then measured for 48 hours at 5, 8, 11, 14, and 17℃. The induction level was lowest at 5℃ and generally increased with temperature until 14℃. The induction level was reduced at 17℃, indicating that 14℃ is the highest tolerable temperature for hepatocytes. These data indicate that primary hepatocyte cell culture is under no stress at 5 and 8℃. Temperatures greater than 11℃ induce stress, showing similar induction patterns in both mRNA and protein in hepatocytes. The results suggest that 14℃ is the maximum internal defense temperature of walleye pollock survival.

• Journal of Marine Life Science
• /
• v.7 no.1
• /
• pp.52-54
• /
• 2022

Mitochondrial genomes of three specimens of Gadus chalcogrammus Pallas 1,814 from Korea and Japan were completely analyzed by the primer walking method. They were 16,570~16,571 bp in length, each comprising 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes. Their gene orders were identical to those of conspecific specimens, but exhibited unique haplotypes. In the phylogenetic tree, the juvenile Korean and adult Japanese specimens were separated from the dominant clade composed of specimens from Japan, Korea, the Bering Sea, and the Arctic, including the adult Korean specimen.

• Journal of Marine Life Science
• /
• v.8 no.2
• /
• pp.160-165
• /
• 2023

This study describes the light microscopical cell types and histochemical characteristics as a preliminary study for the research on integument of the walleye pollock Gadus chalcogrammus in accordance with the physiological and environmental changes. The lateral line of the integument surface showed a curve in the anterior part and was straight from the middle to the posterior part. Integument is composed of outer epidermis and inner dermis. The epidermis is a stratified layer composed of epithelial cells, mucous cells, and club cells. Epithelial cells are classified into squamous superficial cell, cuboidal intermediated cell and columnar basal cell. The thickness of epidermis was 122.9 ㎛, and the ratio of epidermis thickness to body length was 0.03%. The mucous cell and club cell of unicellular gland were mainly distributed in the apical and middle layer of epidermis. The mucous cell contained mucosal materials of acidic glycoprotein. The proportion of mucous cells and club cells were 21.3 (± 7.0)% and 4.0 (± 1.0)% of epidermal area, respectively. The dermis was dense connective tissue layer and composed of mainly collagen fibers. It also contained fibrocytes, blood vessels, melanophores and scales.

• Journal of fish pathology
• /
• v.32 no.2
• /
• pp.69-80
• /
• 2019

We performed MLSA (multilocus sequence analysis) and phenotypic characterization of Aliivibrio species isolated from walleye pollock (Gadus chalcogrammus) maintained in 3 different facilities of Gangwon Province, the east coast of Korea. Of 38 Aliivibrio species identified by 16S rDNA sequences, 12 strains were randomly selected and MLSA was conducted with 5 house-keeping genes (gapA, gyrB, pyrH, recA and rpoA) and 16S rDNA gene. Phylogenetic analysis and homology of the concatenated sequences (4,580 bp) with other Vibrionaceae genera revealed that 4 strains (GNGc16.1, YYGc16.1, YYGc16.2, GSGc18.1) were identified as Aliivibrio logei and one strain (GSGc16.1) as A. wodanis. One strain (GSGc17.1) was tentatively identified as A. logei, but needs further analysis because it did not belong to the same clade with A. logei type strain. 6 strains (GSGc17.2, GNGc16.2, GSGc16.2, GSGc17.3, GSGc18.2, GSGc17.4) need further investigation as potential novel species. Either phenotypic characterization or 16S rDNA sequence alone did not provide enough information for identification of Aliivibrio strains at the species level. A. logei and A. wodanis are generally known as non-pathogenic bacteria, but also known as opportunistic or secondary pathogens of cold water fishes. Cares should be taken to prevent potential outbreaks due to these bacteria, although there was no outbreaks during the sampling period.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.50 no.1
• /
• pp.65-76
• /
• 2017

Since the late 1990s, walleye pollock Gadus chalcogrammus fisheries in Korean waters have been considered collapsed. Although many fisheries scientists suspect that the collapse might have been triggered by overexploitation of juvenile pollock or environmental changes, such conjectures have been neither tested nor investigated, partially because of limited data on the population. There has been no survey of the population, and the ages of fish in fishery catch have rarely been identified. Instead, fishery catch data from 1975-1997 included information about two life stages, 'juveniles and adults,' and data on catch-per-unit-effort (CPUE) during 1963-2007 and those on fish length and weight during 1965-2003 had been sporadically collected from commercial fisheries. To test hypotheses about the collapse of the pollock fisheries, we used a statistical linear model with juvenile CPUE as the response variable, and abiotic (e.g., water temperatures) and biotic factors [e.g., adult pollock, flatfishes (Pleuronectidae sp.), and sandfish (Arctoscopus japonicus) CPUEs] as the explanatory variables. The model results indicated that depletion of the pollock population was associated with both biotic (adult pollock and flatfishes abundance) and abiotic factors (mid-water temperatures in February and October). We further interpreted the results from ecological and biological perspectives, suggesting possible mechanisms.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.53 no.6
• /
• pp.894-899
• /
• 2020

This study investigated the effects of inclusion of pollock oil (PO) in the diet of broodstock on the egg and larval quality of Walleye Pollock Gadus chalcogrammus. The experimental diet comprised of semi-moist pellets prepared either with or without PO (control; Con). The fish assigned to each diet were fed to visual satiation (two meals per day) for 12 weeks. Eggs spawned from both groups of fish were sampled during the spawning season (three months) and the egg and larval quality was determined. Total egg volume, fertilization, and hatchability of eggs from the PO group were higher than those of the Con group. Fatty acid composition of fertilized eggs was not affected by the experimental diet. Oleic acid, eicosapentaenoic acid, and docosahexaenoic acid content in larvae of the PO group was higher than that in larvae of the Con group. These results demonstrate the beneficial effects of including PO in the broodstock diet of Walleye Pollock, specifically on the quality of the eggs (total egg volume, fertilization, and hatchability) and larvae (fatty acid composition).

• Journal of fish pathology
• /
• v.31 no.1
• /
• pp.9-13
• /
• 2018

We previously monitored nervous necrosis virus (NNV) in brain samples of artificially produced walleye Pollock (Gadus chalcogrammus) seedlings, with a low prevalence (1.8%, 1/55) but no clinical symptoms. Given that this virus is considered one of the most serious viral threats for almost all marine aquaculture fish species and characterized by both vertical and horizontal transmission, it would be interesting to monitor NNV in the fertilized eggs as well. We collected fertilized walleye pollock eggs from the farms located in Goseong during January to March, 2017. Approximately 50 mg of eggs were periodically taken from 4 each different batches, and 37 different pooled sample sets in total were made during sampling period. RNA was extracted from the eggs by using Trizol and cDNA was synthesized for RT-PCR for detecting NNV. Primers and PCR conditions are the same as previously described. As a result, NNV was not detected from any of the sample sets by one step PCR (0%, 0/37), suggesting NNV may not be a threat in walleye pollock aquaculture in Korea at present time. However, continuous monitoring for NNV should be conducted because introducing a new species into aquaculture industry involves potentials of disease outbreak and NNV is already known to cause outbreaks in gadoid fishes.

• Journal of fish pathology
• /
• v.31 no.2
• /
• pp.71-79
• /
• 2018

Wild walleye pollock were caught from Goseong, The East Sea of Korea and examined for the existence of several fish pathogenic viruses; viral hemorrhagic septicemia virus (VHSV), nervous necrosis virus (NNV) and marine birnavirus (MABV). We collected 1,253 wild walleye pollock in total during February 2015 and August 2018. 324 spleen sample sets and 259 brain sample sets were made, and examined for the existence of the viruses mentioned above by reverse transcriptase polymerase chain reaction (RT-PCR). None of the target viruses were detected by one-step PCR. When some of these samples were further examined by two-step PCR, 19.7% (36/183) of spleen sample sets were positive for VHSV, and 4.4% (8/183) of spleen sample sets and 1.2% (3/259) of brain sample sets were positive for NNV. The target sequences of these viruses were clustered with those previously reported in Korea (Genotype IVa of VHSV, RGNNV genotype of NNV) by phylogenetic analysis. The activity of these viruses are not clear because virus isolation was not attempted, but probably very low because all the positive samples were detected by two-step PCR.