• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.44 no.1
• /
• pp.58-63
• /
• 2011

This study investigated the effects of stocking density and feeding frequency (three and five times per week) on the growth of Pacific cod, Gadus macrocephalus. In the first experiment, experimental groups of fish (mean weight $167.8{\pm}41.4\;g$) were reared at three stocking densities (4, 8 and 12 kg/$m^3$) for 16 weeks. The total weight gain was 17.8, 17.1 and 35.4% at 4, 8 and 12 kg/$m^3$, respectively. The specific growth rates, survival rates and feeding efficiency increased with the density, but there were no significant differences (P>0.05). The daily feed intake decreased as the stocking density increased, whereas the condition factors increased with the stocking density (P<0.05). In the second experiment, groups of fish ($194.1{\pm}68.3\;g$) were fed either three or five times a week. The total wight gain was 14.4 and 18.5% for the fish fed three and five times per week, respectively. The specific growth rates of Pacific cod fed to satiation increased with the feeding frequency, although the difference was not significant (P>0.05). The survival rates, daily feed intake, feed efficiency, and condition factors of the Pacific cod were not significantly different (P>0.05). Based on these results, the optimum stocking density for juvenile cod is above 12 kg/$m^3$, and the best feeding frequency is three times a week, under the conditions used in this experiment.

• Korean Journal of Ichthyology
• /
• v.31 no.4
• /
• pp.195-200
• /
• 2019

An experiment was performed to obtain cryopreservation techniques of Pacific cod Gadus macrocephalus sperm. Milt were cryopreservation using five cryoprotectant demethyl sulfoxide (DMSO), ethylene glycol (EG), glycerol, methanol and propylene glycol (PG) with marine fish ringer's solution (MFRS) as diluent. Milt were cryopreserved each experimental methods like cryoprotectants (10% and 20%), equilibration time (3, 5 and 10 min) and freezing protocols (liquid nitrogen vapor above 3, 8 and 12 cm). Post-thaw sperm survival rate revealed the highest in 10% PG with optimum methods of equilibration time (3 min) and freezing protocol (liquid nitrogen vapor above 8 cm) about 21.3±1.8%. Hatching rate of fertilization eggs using fresh and cryopreserved sperm were no significantly different.

• Korean Journal of Ichthyology
• /
• v.21 no.1
• /
• pp.28-37
• /
• 2009

The diet of Pacific cod (Gadus macrocephalus) in the East Sea, Yellow Sea and Jinhae Bay was studied by analysis of stomach contents. In total, 518 individuals ranging from 15.5 to 77.0 cm standard length SL were analyzed. Prey organisms of the Pacific cod in the East Sea consistedof Caridea, Cephalopoda and Pisces, whereas In the Yellow Sea, the main food items of Pacific cod were similar to those of East Sea Pacific cod except for Cephalopoda. Interestingly, the stomach contents of Pacific cod in Jinhae Bay is mainly Pisces, which is in contrast to those of the two different coastal areas, the East Sea and the Yellow Sea. Although various species of food were eaten by smaller Pacific cod, both Caridea and Pisces were mainly taken by larger Pacific cod. Consequently, the diet of Pacific cod within acertain size is mainly influenced by prey abundance and prey-size spectrum in its habitat. Higher stomach emptiness of Pacific cod in Jinhae Bay might indicate that fully matured Pacific cod temporally stop feeding during their spawning period.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.42 no.1
• /
• pp.63-67
• /
• 2009

The effects of adhesive substrates and bottom materials on the release of fertilized eggs by the Pacific cod, (Gadus macrocephalus) were examined to find an effective release method. Palm twin as an adhesive substrate displayed a significantly elevated adhesive rate compared to gulf weed. However, the survival rate of the fertilized eggs attached to palm twin was as low as 17.5% 8 days after fertilization (DAF). In contrast, fertilized eggs in the absence of adhesive substrate displayed the highest survival rate (47.0%). Concerning bottom materials, the survival rate of fertilized eggs on sand was significantly high (approximately 51.1%) on 8 and 9 DAF. The observations indicates that adhesive substrates are not needed and spawning ground bottom materials such as sand or mud should be considered when releasing fertilized eggs of Pacific cod.

• Korean Journal of Ichthyology
• /
• v.29 no.4
• /
• pp.258-260
• /
• 2017

The morphomeristic features of Gadus macrocephalus was compared using fish samples from Jinhae Bay in the South Sea and Boryeong in the Yellow Sea, Korea. In total, 332 individuals were sampled from 2 locations to investigate the differences in the morphomeristic features and determine applicability of it as a means of stcok discrimination of G. macrocephalus. No significant differences in the number of vertebrae, 1st to 3rd dorsal-fin soft rays, 1st and 2nd anal-fin soft rays, pectoral-fin soft ray, pelvic-fin soft ray, and gill raker were found between two populations from Jinhae Bay and Boryeong. The results of present study revealed that morphomeristic features of G. macrocephalus was not applicable for stock discrimination.

• Korean Journal of Ichthyology
• /
• v.22 no.2
• /
• pp.121-125
• /
• 2010

To investigate the relationship between total length and fecundity of Pacific cod Gadus macrocephalus in Jinhae Bay, 45 individuals were sampled during the spawning period from Dec 2008 to Feb 2009. Fecundity ranged from 560,000 to 5,200,000 eggs for fish ranging from 64.0 cm to 74.0 cm in total length. The relationship between total length (TL) and fecundity (F) was F=103,273TL-5,124,302 and fecundity in Pacific cod from this study was correlated with total length. Average fecundity decreased from 2,620,000 eggs in early-spawning period to 1,650,000 eggs in late-spawning period. The wide range of relative fecundity at the same body size indicates that the timing of the spawning migration of Pacific cod in Jinhae Bay could be related to fecundity.

• Korean Journal of Ichthyology
• /
• v.27 no.2
• /
• pp.142-148
• /
• 2015

The feeding habits of the Pacific cod Gadus macrocephalus were studied using 620 specimens collected by bottom trawl and pound net in the Southeast sea of Korea, from February 2012 to June 2013. Of 620 specimens, 192 contained food and 428 were empty. The total length (TL) of individuals used in this study ranged from 20.4 to 95.2 cm. Pacific cod mainly consumed Pisces, Macrura, and Cephalopoda. Its diet also included small quantities of Anomura, Brachyura, Mysidacea, Isopoda and Amphipoda. The proportion of Pisces in prey items increased with increasing Pacific cod length, but seasonal difference was not observed. The proportion of Macrura and Cephalopoda decreased with growth, and seasonal differences were apparent. Macrura were taken there mainly from autumn to winter, whereas Cephalopoda were consumed from spring to summer.

• Korean Journal of Ichthyology
• /
• v.19 no.4
• /
• pp.318-323
• /
• 2007

The feeding habits of Pacific cod (Gadus macrocephalus) were studied based on the examination of stomach contents of 192 specimens collected from November, 2005 to January, 2006 in the coastal waters off Gadeok-do, Korea. The size of Pacific cod ranged from 35 to 82 cm in standard length (SL). Pacific cod mainly consumed shrimps such as Eualus spathulirostris, Crogon hakodatei and C. affinis and fishes. Its diet also included small quantities of cephalopods, amphipods, hermit crabs and crabs. Individuals between 35 cm and 45 cm SL mainly consumed shrimps. The portion of shrimps decreased with increasing fish size, and this decrease was paralleled with increased consumption of fishes and cephalopods. In this study we found Syngnathus schlegeli in the stomach contents of many Pacific cod specimens. S. schlegeli is a typical seagrass fish species which inhabits in seagrass beds, This fact means that Pacific cods stay in the seagrass beds during spawning period. Therefore migration of Pacific cod to coastal waters off Gadeok-do during spawning period seems to be a survival strategy for its larvae and small juveniles to stay in seagrass beds which provide with abundant foods and shelters to many commercial fish species.

• Journal of Aquaculture
• /
• v.20 no.4
• /
• pp.260-264
• /
• 2007

We investigated egg collection and the effects of water temperature (4, 7, 10, 13 and $16^{\circ}C$) on egg development, hatching and larval growth of Pacific cod Gadus macrocephalus under laboratory conditions. Fertilized eggs were round in shape ($1.01{\pm}0.03\;cm$) and adhesive to nylon nets. Fertilization rate was 68% by wet method. The time of egg development was negatively proportional to water temperature with the range of $4^{\circ}C$ to $13^{\circ}C$. Eggs hatched only at $7^{\circ}C$ after 288 hours of fertilization and $10^{\circ}C$ after 192 hours. Hatching rate was highest as 65% at $7^{\circ}C$ followed by $34.4^{\circ}C$ at $10^{\circ}C$. Survival rate was 18.3% at $7^{\circ}C$ and 5.2% at $10^{\circ}C$.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.51 no.3
• /
• pp.332-337
• /
• 2018

The Pacific cod Gadus macrocepahlus, lays demersal eggs and the hatching larvae rise toward the surface layer of the ocean to feed. The change in the specific gravity of eggs and larvae was investigated to examine their vertical distribution and movement in the water column. The specific gravities of fertilized eggs and various size classes of larvae were measured using a density gradient apparatus. In total, the instantaneous specific gravity of 146 eggs and 225 larvae were measured. To prevent any disturbance in the gradient water column due to larval movement, 0.004% MS222 was used for anesthesia. Due to their high specific gravity, eggs spawned were deposited over the sea-bed of the spawning ground. The specific gravity of hatching larvae decreased abruptly. However, Pacific cod larvae still had a comparatively high specific gravity at hatching ($1.03655{\pm}0.00146g/cm3$, n=4, mean SL=3.62 mm) and their specific gravities tended to decrease as they grew. The specific gravity stabilized 6 days after hatching ($1.02590{\pm}0.00212g/cm3$, n=15, mean SL=4.67 mm) and the cod larvae were eventually able to float in the water column.