• Journal of fish pathology
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• v.15 no.3
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• pp.105-110
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• 2002

Thirty five catfish (Silurus asotus) cultured in a fish farm of Jungeup and 222 wild goby (Acanthoguobius flavimanus) caught from the estuary of Mankyoung River, Chonbuk province of Korea were examined the prevalence of myxosporidian infestation. A lot of white spherical myxosporidian cysts in the intestinal epithelium of catfish and the muscle of goby were easily found. The cysts in size were 56 × 73 (42-77 × 59-93 ㎜) in catfish and 2.43 × 0.95 ㎜ in goby. The infection rate (%) were 88.4 in catfish and 89.4 in goby. The Myxosporidians from the intestine of catfish and from the musculature of goby were identified as Myxoborus miyairii and Henneguya tridentigeri on the basis of the shape and structure of the spores under a light microscope. imensions (㎜) of fresh spores of Myxoborus miyairii: length, 11.0-12.0; width, 5.0-6.0; thickness, 3.5-4.0; polar capsule: length, 5.0-5.5; thickness, 1.5-2.0; polar filament: length, 40-45. Dimensions ($\mu{m}$) of fresh spore of Henneguya. tridentigeri: length, 10.0-12.0; width 6.0-8.0; thickness, 4.8; polar capsule: length, 4.6; thickness, 2.6; iodinophilic vacuole: 2.8 × 2.4. No significant pathological change was found from the infected fish. This is the first report on M. miyairii and H. tridentigeri from fish species in Korea.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.3
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• pp.220-231
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• 2016

Yield-per-recruit (YPR) analysis is used to provide management guidance for the efficient use of a fish cohort. However, the individual fish price per unit weight of small yellow croaker (Larimichthys polyactis) or hairtail (Trichiurus lepturus) increases dramatically by size in Korea. Therefore, age-based production value-per-recruit (PPR) analysis has recently been developed (Zhang et al., 2014). Since age determination requires a substantial amount of money and time and it is even impossible for some fish species, it is difficult to obtain age information to apply the age-based PPR model. Thus, we attempted to develop an alternative method, which uses length data rather than age information, called the length-based PPR analysis. The results revealed that length-based PPR analysis was much more conservative for stock management than the YPR analysis. Furthermore, the PPR analysis was more economically beneficial than the YPR analysis, which can prevent the fish stock from the economic overfishing. In conclusion, the length-based PPR analysis could be a proper approach for stock assessment in the case that the individual fish price per unit weight increases dramatically by size, and this analysis is useful to obtain vital management parameters under data-deficient situation when traditional stock assessment methods are not applicable.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.3
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• pp.214-221
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• 2011

This study was performed to develop a video based system which can be used to measure the averaged fish size in a non-intrusive fashion. The design was based on principles of simple stereo geometry, incorporated fish dimensions weight relationships and took into consideration fish movement to lower system costs. As the fish size is an important factor that impacts the economy of an aquaculture enterprise. Size measurements, including fork length, width or height, girth, thickness and mass, can be used to determine fish condition in the fish farm, so the averaged fish size of fish cage needs to consistently monitor in open ocean aquaculture cage. A precision of ${\pm}3%$ for replicate length measurements of a 60cm bar is obtained at distances between 2.0 and 6.0m, and the mean fork length and mean swimming speed of bluefin tuna were estimated to 48.8cm and 0.78FL/s, respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.4
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• pp.347-359
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• 1992

The movements of three striped jack (Caranx delicatissimus, 24cm of body length) were tracked by ultrasonic telemetry in the Nunoura Bay in August 1990. A school of the striped jack has been released near by the fish farming rafts by Goto branch of the Fisheries Agency and Japan Sea-Farming Association. To investigate the staying area and the swimming pattern of the fish, small size pinger($\Phi$8.5$\times$L35mm, 140dB re 1$\mu$Pa at 1m, 69kHz) was tagged on the dorsal fin without any anesthesia. The movements of three tagged fish are monitored at the same time with four omni-directional hydrophones. The locations of the fish are calculated by the hyperbolic method and tracked by a technique so called time division scheme which uses both the pulse interval and the phase. Three pingers used have the pulse interval of 1.7, 1.8 and 1.9sec, respectively, and the common pulse duration of 15ms. In results it was capable to estimate behavior right after the release, swimming speeds and approximate moving area of the fish. The movements were tracked for a week continuously, and it was found out that the staying area of the fish was around or under the farming rafts. Sometimes they swam together but most of the time they move separately. The average swimming speed of those fish was about two times of the body length.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• v.3 no.1
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• pp.47-53
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• 2022

The escape behavior of prey fish to predator attack is directly linked to the survival of the fish. In this study, I explored the escape behavior of Medaka fish to bird attacks. To simulate the attack, I designed a model triangular-shaped bird to slide along a fishing line connected between rods at both ends of the tank. The triangular shape was set to 10×15 (S=1), 15×20 (S=2), and 20×25 cm (S=3) with base×height. The slope (θ) of the fishing line, which determines the attack speed of the model bird, was set to values of 15° (θ=1), 30° (θ=2), and 45° (θ=3). The escape behavior was characterized using five variables: escape speed (ν), escape acceleration (α), responsiveness (γ), branch length similarity entropy (ε), and alignment (ϕ). The experimental results showed when (S, θ)=(fixed, varied), the change in values of the five variables were not significant. Thus, the fish respond more sensitively to S than to θ In contrast, when (S, θ)=(varied, fixed), ν, α, and γ showed increasing trends but ε and ϕ did not change much. This indicates the nature of fish escape behavior irrespective of the threat is inherent in ε and ϕ. I found that fish escape behavior can be divided into two types for the five physical quantities. In particular, the analysis showed that the type was mainly determined by the size of the model bird.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.3
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• pp.239-248
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• 2003

This paper was conducted as an attempt in order to construct the data bank of target strength for acoustic estimation of fish length in the coastal waters of Korea. The fish length dependence of acoustic target strength for 13 large yellow croakers (Pseudosciaena crocea) at 75 kHz was investigated and the prediction of the target strength by using the Kirchhoff-Ray Mode model (KRM model) was compared with target strength measurements. The results obtained are summarized as follows; 1. In the averaged target strength pattern for 13 large yellow croakers the maximum target strength was -35.13 dB at $-13.35^{\circ}$ on a tilted angle. 2. The relationship between fork length(L, cm) and averaged target strength(TS, dB) was expressed as follows; TS=23. 76log (L) -73.45 (r=0.47) TS=20log(L) -67.35 From this result, the conversion coefficient was -73.45 dB and 6.1 dB lower than the coefficient -67.35 dB where the value of the slope of the regression equation is forced to be 20. 3. Averaged target strength and a length conversion coefficient derived from a target strength histogram for 13 large yellow croakers of mean length 25.59 cm were -41.23 dB, -69.72 dB, respectively. 4. In the range of $$2;{\ll} L (fish length /{\lambda}(wave length);{\ll}40$$, the prediction of the averaged target strength by the KRM model increased gradually with the increasing of $L/{\lambda}$ and was lower than the measured target strength.

• Korean Journal of Ichthyology
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• v.32 no.2
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• pp.55-62
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• 2020

The Relative weight index is an index for evaluating nutritional condition of fish by calculating a ratio of observed weight to standard weight. The purpose of this study is estimating standard Length-Weight relationships (standard LWRs) to calculate standard weight for application of relative weight index and analyze frequency distribution of relative weight index of 10 freshwater fish in the South Korea. The standard LWRs for each species was calculated by the Length-Weight data sets from 798 times of captures at 141 sites. The correlation of determination (r²) for all species was over 0.9 and values of parameter b were within the expected range according to Froese (2006). We calculated in increments of 10 from 10 to 90 percentile of relative weight index for each species, and it could be used as a standard for quantitative assessment of nutritional condition of freshwater fish.

• 한국해양학회지
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• v.4 no.1
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• pp.17-35
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• 1969

This work concerns morphological studies of the Japaness jack mackerel, Trachurus japonicus(Temminck & Schlegel). A total of 48 random samples consisting of 2669 fish is examined, representing three geographic regions, namely, Kamakura, Nagasaki, and Tottori. Preservation affects length and weight of fish considerably, but the variability after 10 days is shown to be negligible. The variability in measuring the morphometric characters due to different measures and orders is found to be significant. They are relatively small, however, compared to the variability in mean length to be expected in samples drawn from the population. Two meristic characters, namely, anal and second dorsal fin rays and three morphometric characters, namely, head length, first and second dorsal insertion distances are chosen for the study. Results of the statistical analysis reveal that differences in the selected meristic characters among samples within and between regions are found to be significant. In general, it is reasonable to state that the jack mackerel collected in Nagasaki region, on the average, have greatest number of anal fin ray and second dorsal fin ray followed by Kamakura, and Tottori regions in that order. It is found that although no significant differences in the slope of regression line are noticed, the mean differences of the selected morphometric measurements in relation to fish length are found to be significant among samples within each region. Differences in the regression coefficients as well as the adjusted sample means are found to be significant between regions. The analysis suggests that samples from Nagasaki region, on the average, have longest head length and greatest distances from snout to the insertion of first dorsal and second dorsal fins followed by Kamakura, and Tottori regions in that order.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.5
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• pp.790-793
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• 2020

Length-weight relationships (LWR) for 27 fish species inhabit Southern sea in Korea were investigated to describe several biological characters. Total 7,399 individuals were collected by R/V Tamgu-20 using bottom trawl between 2018 to 2019 and were identified as 19 families and 27 species. Parameter b ranged from 2.414 to 3.472. Thirteen species among 27 species showed isometric growth (b=3), six species showed negative allometry (b<3) and eight species showed positive allometry (b>3). The results of this study provide useful basic biological information about 27 fishes and are highly reliable due to use of data measured directly.

• Korean Journal of Environment and Ecology
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• v.29 no.1
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• pp.29-45
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• 2015

Water chemistry and fish community, based on fish compositions and ecological characteristics(trophic/tolerance guilds and condition factor), were compared in Gucheon Reservoir($G_cR$) and Yeoncho Reservoir($Y_cR$). Chemical parameters of water quality such as BOD, COD, nutrient(N, P) and suspended solids indicated that water quality was better in the $Y_cR$ than $G_cR$, and the temporal variability in seasonal and interannual patterns were greater in the $Y_cR$. The greater variability was mainly attributed to intense dilutions of reservoir water by Asian monsoon rain during July-August. Fish guild analysis indicated that species diversity was higher in the $G_cR$ than the $Y_cR$, and that the proportion of tolerant and omnivore species were greater in the $Y_cR$. Regression analysis of body weight-total length showed that the regression coefficient(b value) was lower in the $G_cR$(2.15 ~ 2.40) than the $Y_cR$(2.59 ~ 3.14). Condition factor(K) of fish against the total length showed negative slope of Zacco temminckii, Carassius auratus, Pseudorasbora parva and Rhinogobius brunneus population in the $G_cR$, and a positive slope of Carassius auratus and Rhinogobius brunneus population in $Y_cR$. Overall, our data suggest that the growth of the fish populations, based on the length-weight relations and condition factor, reflected the trophic regime of nutrients and organic matter.