• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.1
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• pp.9-18
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• 2020

We investigated the maturity and spawning dynamics of chub mackerel Scomber japonicus in Korean waters using samples collected by a large purse seine fishery from January 2013 to December 2017. We analyzed sex ratio, monthly maturity stage, gonadosomatic index (GSI), Fulton's condition factor (K), and fork length at 50% group maturity. Spawning occurred from March to June, with a peak in May. We detected a significant difference in sex ratio (χ² test, P<0.05). The relationship between fork length and body weight was expressed as BW=0.0025FL^3.4693. We estimated 50% group maturity at a female fork length of 29.3 cm.

• Korean Journal of Veterinary Research
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• v.56 no.1
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• pp.45-46
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• 2016

For several days, there was a series of mortalities of chub mackerel (Scomber japonicus) that were reared for public exhibition in a private aquarium in Seoul, Korea. As part of the diagnosis of the dead fish, a bacterial isolate from the kidney was cultured, identified, and confirmed to be Vibrio (V.) harveyi using Vitek System 2 and 16S rRNA gene sequencing. Phylogenetic analysis was also performed by the neighbor-joining method. As a result, the V. harveyi isolated from chub mackerels of a private aquarium in Korea, called as SNUVh-LW1, was clustered in the same group with V. harveyi ATCC33843.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.25 no.1
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• pp.12-17
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• 1989

A field experiment was carried out of confirm the effect of underwater sound on the luring of fish school of chub mackerel in the coast of Idousyo Island. Underwater sound that was made use of luring of fish school was pure sound and interval pure sound which the frequencies of the sound were 150Hz and 200Hz, respectively. The results of the observation of hooking and recording paper of fish finder indicate that the effect of emitting sound at 20m in the depth of water was remarkable for the luring of fish school of chub mackerel. The vertical pure sound pressure level at 150Hz and 200Hz of the water layer that was lured the fish school of chub mackerel were 140.1dB and 146.dB at 30m, 121.0dB and 126.6dB at 70m and 141.9dB and 120.5dB at 120m in the depth of water, respectively.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.1
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• pp.73-79
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• 2021

The feeding habits of Chub mackerel Scomber japonicus were investigated using 329 specimens collected from coastal waters of the South Sea of Korea. S. japonicus is mainly a piscivore, consuming small fish such as Engraulis japonicus (%RI: 81.0 %). The diet of Chub mackerel also includes small quantities of thaliaceans, euphausiids, and amphipods. We calculated the trophic level as 3.92 for S. japonicus. The dietary composition of S. japonicus did not show significant differences with size, but differed with season. As the body size of S. japonicus increased, the mean weight of prey within the stomach (mW/ST) increased (One-way ANOVA, P<0.05).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.6
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• pp.730-733
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• 2012

We investigated body shrinkage, defined as change in standard length and body weight of juvenile chub mackerel Scomber japonicus after preservation in 70% ethyl alcohol for 1, 8, or 12 days. Standard length (SL) was decreased by 3.6% and body weight (BW) was reduced by 27.5% after 8 day of preservation. There were no significant decreases in SL and BW after 8 or 12 days preservation. Linear regression equations for estimation of original body size from the size after preservation in 70% ethyl alcohol for 12 days were expressed as: $SL_{original}=0.96SL_{preserved}+5.17$ and $BW_{original}=1.16BW_{preserved}+0.37$. These equations will be useful for improving accuracy the estimation accuracy for various size-related biological parameters in juvenile chub mackerel juvenile.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.6
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• pp.942-953
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• 2020

Achieving optimal sustainable yields (i.e., avoiding overfishing and maximizing fishery harvest at the same time) is one of the main objectives in fisheries management. Generally, management reference points (MRPs) such as fishing mortalities (Fmsy, F0.1, Fx%) have been suggested for the purpose. In this study, we intended to suggest MRPs for Korea chub mackerel Scomber japonicus stock, using a stochastic catch-at-age model (SCAA) and evaluate whether the current fishing intensity on the stock is appropriate. We used length frequency and catch-per-unit-effort data on the Korea chub mackerel stock collected from the large purse-seine fishery, and yields landed by all fisheries from years 2000 - 2019. We calculated yield per recruit and spawning potential ratio, and projected spawning stock biomass (SSB) under different fishing mortality, assuming annual recruitments were solely controlled by environmental effects (i.e., steepness of 1.0). Some of our major findings and suggestions were that the overfishing threshold would be F46%; i.e., the fishing mortality in the terminal year, 2019 was 0.257/year, which corresponded to F46%.

• Fisheries and Aquatic Sciences
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• v.24 no.4
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• pp.139-152
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• 2021

The main purpose of this study is to fit catch-per-unit-effort (CPUE) data about Korea chub mackerel (Scomber japonicus) stock with a state-space production (SSP) model, and to provide stock assessment results. We chose a surplus production model for the chub mackerel data, namely annual yield and CPUE. Then we employed a state-space layer for a production model to consider two sources of variability arising from unmodelled factors (process error) and noise in the data (observation error). We implemented the model via script software ADMB-RE because it reduces the computational cost of high-dimensional integration and provides Markov Chain Monte Carlo sampling, which is required for Bayesian approaches. To stabilize the numerical optimization, we considered prior distributions for model parameters. Applying the SSP model to data collected from commercial fisheries from 1999 to 2017, we estimated model parameters and management references, as well as uncertainties for the estimates. We also applied various production models and showed parameter estimates and goodness of fit statistics to compare the model performance. This study presents two significant findings. First, we concluded that the stock has been overexploited in terms of harvest rate from 1999 to 2017. Second, we suggest a SSP model for the smallest goodness of fit statistics among several production models, especially for fitting CPUE data with fluctuations.

• Applied Microscopy
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• v.30 no.4
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• pp.321-326
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• 2000

The ultrastructure of the fertilized egg envelope from pale chub , Zacco platypus belong to Cyprinidae was studied using scanning and transmission electron microscopes. The fertilized egg was an adhesive type, have a single micropyle resembling the pathway of sperm in the area of the animal pole. The micropyle was surrounded by 5 peaks of hill. An outer surface of the fertilized egg envelope was arranged by pore canals irregularly. In section of fertilized egg, the egg envelope consistes of three layers, an outer adhesive layer, a middle electron dense layer and an inner lamellae layer consisting of 9 layers. These ultrastructural characters of fertilized egg envelope from pale chub can be utilized in taxonomy of teleost.

• Fisheries and Aquatic Sciences
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• v.18 no.3
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• pp.301-309
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• 2015

Chub mackerel, Scomber japonicus, larvae and juveniles were reared from hatching to 35 days after hatching (DAH), and the development of their digestive systems was histologically investigated. The larvae were initially fed on rotifers and Artemia nauplii starting around 19 DAH, and thereafter on Artemia nauplii, fish eggs, and a formulated feed mixture. The primitive digestive system differentiated at 3 DAH; the digestive tract was distinctively divided into the buccopharyngeal cavity, esophagus, stomach, air bladder, intestines, and rectum. The gastric gland and pyloric caeca first appeared at 5 and 7 DAH, respectively. The stomach was divided into cardiac, fundic, and pyloric regions in the preflexion phase. The number of gastric glands and pyloric caeca, as well as the volume of the gastric blind sac increased markedly, with development continuing into the juvenile stage. The precocious development of the digestive system during the larval period might be related to the early appearance of piscivory, which is able to support high growth potential. The organogenesis results obtained for this precocial species represent a useful tool to aid our understanding of the physiological requirements of larvae and juveniles to ensure optimal welfare and growth under aquaculture conditions, which will improve current rearing practices of this scombrid species.

• Fisheries and Aquatic Sciences
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• v.17 no.2
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• pp.175-180
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• 2014

The present study was conducted to characterize physicochemical properties of chub mackerel bones (CMB) to evaluate its potential as a food resource. The proximate composition of CMB showed 40.4% moisture, 13.8% crude fat, 15.2% crude protein, and 28.7% ash. The major minerals in CMB were calcium (26.27 g/100 g) and phosphorus (15.88 g/100 g). The amino acids were rich in glycine, proline, glutamic acid, and alanine. The contents of total and neutral lipids, glycolipid and phospholipid were shown to be 16.05%, 95%, 2.32%, and 3.15%, respectively. The major fatty acids were C22:6, C16:0, C18:1, C20:5, C18:0, C17:0, C14:0, C20:1 in order. The fatty acid contents of total and neutral lipid were in a range of 39.25% and 44.54% for saturated and 33.61% and 34.05% for polyunsaturated, respectively. The breaking strength and hardness of intact CMB were 10.01 and $50.03kgf/cm^2$, whereas those of CMB heated for 45 min at $121^{\circ}C$ were 0.40 and $1.94kgf/cm^2$, respectively.