• Fisheries and Aquatic Sciences
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• v.25 no.5
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• pp.298-310
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• 2022

Although giant and large fish species are highly important as a keystone species in the marine ecosystem, there have been no or few studies on their spatio-temporal variations around the Korean peninsula. For this, we analyzed daily reports made by observers at 57 fishery landing sites in Korea over 6 years, from 2011 to 2016. In total, 153 fish species were re-identified based on photos and descriptions recorded by Korean observers, of which five species were classified as a giant fish over 5 m in maximum total length (MTL) and 17 species as a large fish from 3 m to 5 m MTL according to the data presented by Froese & Pauly (2021). Among the giant and large fish species, Mola mola was the most abundant species, with 75 individuals landed as by-catch. The second most abundant species was Isurus oxyrinchus (31), followed by Mobula mobular (23), Lamna ditropis (17), Masturus lanceolatus (16), Sphyrna zygaena (14), and Prionace glauca (12). As a result of cluster analysis based on the number of individuals of giant and large fish species by year and sea, six years were separated into two clusters (2011-2013 vs. 2014-2016), with high contribution of M. mola, I. oxyrinchus, and M. lanceolatus; and three seas were separated into two clusters (eastern + southern seas vs. western sea), with high contribution of M. lanceolatus, L. ditropis, and I. oxyrinchus. The largest number of M. mola accounted for 64% of the total in 2014 and 2016, and 71% in summer (June-August). It is assumed to have a correlation between seawater temperature fluctuation and the occurrence of giant and large fish species. Our study highlights importance of longterm monitoring of giant and large fish species, and can help to understand the life cycle such as natal or nursery migration of giant and large fish species around the Korean peninsula.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.6
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• pp.762-769
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• 2017

This study investigated the effects of stocking density on the growth of the mandarin fish Siniperca scherzeri, in small (1-year old, 50.2 g/fish) and large (2-years old, 173.1 g/fish) size (age) groups. Small and large fish groups were fed pelleted diets twice daily for 10 and 15 weeks, respectively. In the small group, at the end of the feeding, the weight gain of fish at a density of $4kg/m^3$ was lower than that of fish at densities of 3, 2 and $1kg/m^3$. However, fish stocking density did not affect feed efficiency. The daily feed intake of fish at a density of $4kg/m^3$ was lower than that fish at densities of 3, 2 and $1kg/m^3$. In the large fish group, the weight gain of fish at a density of $4.5kg/m^3$ was higher than that of fish at densities of 6, 3 and $1.5kg/m^3$. Again, fish stocking density did not affect feed efficiency. The daily feed intake of fish at a density of $4.5kg/m^3$ was higher than that of fish at densities of 6, 3 and $1.5kg/m^3$. Based on these results, the optimum stocking density for small (50.2 g/fish) and large (173.1 g/fish) mandarin fish is 3 and $4.5kg/m^3$, respectively.

• Korean Journal of Ecology and Environment
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• v.34 no.4 s.96
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• pp.310-318
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• 2001

In the large regulated Nakdong River, the Predation effect of juvenile fish on the zooplankton community was evaluated by gut and stomach analyses of fish in 1999. Juvenile fish of five species showed high density from May to early June when river discharge was low and water body became stagnant. During this period, large rotifers, Asplanchna spp. and Brachionus spp. declined and the decrease of cladoceran (Moina micrura and Bosminopsis deitersi) density was also obeserved. At this time, small rotifers including Polyarthra spp. reached maximum density. Gut analysis of fish demonstrated that small-sized juvenile fish (< 15 mm in total length)preferred large rotifers as well as cladocerans, while large sized fish (> 15 mm)selected only cladocerans. On the other hand, juvenile Micropterus salmoides of which size was larger than other juvenile fish consumed not only zooplankton but also other small juvenile fish. Based on these results, the decline of large rotifers and cladocerans during early summer in the river seems to be result of predation by juvenile fish. However, the period when juvenile fish maintained their high density was as short as one month and the decreased density of cladocera rapidly recovered as soon as juvenile fish became scarce. Such a short period of juvenile fish devel-opment in the river can be attributed to the consumption of juvenile fish by the young-of-the-year cohorts as well as adults of M. salmoides. The high trophic state of the river might permit the rapid recovery of the cladoceran community. The predation impact of juvenile fish in the Nakdong River seems to be affected by the existence of piscivore as well as high trophic status.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.5
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• pp.411-416
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• 2009

Proximate compositions and fatty acid profiles of cultured and wild mackerel (Scomber japonicus) muscles were compared. Protein content ranged from approximately 16% to 18% and was higher in wild fish than in cultured ones. Lipid content was between two to four times higher in large and small cultured fish (20.1-20.5%) compared with same sized wild fish. The prominent non-polar lipid (NL) class in fish muscles was triglyceride, and additionally, free sterol was among the prominent NL classes in wild fish muscles. Prominent phospholipid (PL) classes in cultured and wild fish muscles were phosphatidylethanolamine and phosphatidylcholine, with the former being higher in cultured fish and the latter higher in wild fish. Prominent fatty acids of total lipid were 16:0, 18:1n-9, 22:6n-3 (docosahexaenoic acid, DHA), 20:5n-3 (eicosapentaenoic acid, EPA), 16:1n-7, 18:0 and 14:0, while 18:2n-6 was among the prominent fatty acids in cultured fish. The n-3 polyunsaturated fatty acids (PUFA, DHA+EPA) content (in mg/100 g of muscle tissue) was higher in cultured fish (2,711 mg in large fish and 2,572 mg in small fish) than in wild fish (2,431 mg in large fish and 1,398 mg in small fish). In conclusion, we have been able to demonstrate that cultured mackerel could also be a good sources of n-3 PUFA, such as DHA and EPA.

• Development and Reproduction
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• v.23 no.2
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• pp.183-191
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• 2019

The objective of this study is to evaluate the anesthetic effects of clove oil and tricaine methanesulfonate (MS-222) on the Far Eastern catfish, Silurus asotus, by measuring the times to anesthesia and recovery. Each anesthetic effect of clove oil and MS-222 was tested in two groups of fish with different body sizes: a group of small fish (mean body length: $15.5{\pm}1.58cm$, mean body weight: $50.1{\pm}5.91g$, n=20) and a group of large fish (mean body length: $31.5{\pm}4.19cm$, mean body weight: $302.1{\pm}15.22g$, n=20). The anesthetics were used at concentrations of 200, 300, 400, 500, and 600 ppm. The results showed significant relationships between the concentration of the anesthetic and the body size of the fish. Each of these variables showed statistical significance (p<0.05). The time to anesthesia decreased linearly with increasing concentration in the large fish for both clove oil and MS-222 (p<0.05). Based on an optimal anesthetic time of approximately 1 min, the preferred concentrations of the anesthetics were 500 ppm for clove oil and 600 ppm for MS-222. Both the anesthetic time and the recovery time were shorter for the small fish than for the large fish (p<0.05). Our study showed that the smaller-sized Far Eastern catfish was more easily anesthetized and recovered more rapidly from anesthesia than the larger-sized fish.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.50 no.1
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• pp.30-38
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• 2014

Hydro-acoustic survey was carried out to investigate the spatial characteristics of fish distribution near two artificial reefs (AO: large octagonal semi-sphere and AC: combined custom built) having different types in Jeju marine ranching area. The survey system consisted of scientific echo sounder (EK60), DGPS system, and ECDIS (Mecys). Field survey was conducted on August and October 2012 with star survey and line transect survey line method, and species composition was investigated from gill net fishing survey. The acoustic signals from individual fishes and small fish schools were mainly recorded around AO, but large and strong signals from large fish school were mainly detected in the top layer of and the water column near AC. The echogram suggest that the fish aggregation for the two types of AO and AC exist the significant difference in fish species and spatial distribution pattern.

• Journal of information and communication convergence engineering
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• v.18 no.2
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• pp.106-114
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• 2020

We propose appropriate criteria for obtaining fish species data and number of learning data, as well as for selecting the most appropriate convolutional neural network (CNN) to efficiently classify exotic invasive fish species for their extermination. The acquisition of large amounts of fish species data for CNN learning is subject to several constraints. To solve these problems, we acquired a large number of fish images for various fish species in a laboratory environment, rather than a natural environment. We then converted the obtained fish images into fish images acquired in different natural environments through simple image synthesis to obtain the image data of the fish species. We used the images of largemouth bass and bluegill captured at a pond as test data to confirm the effectiveness of the proposed method. In addition, to classify the exotic invasive fish species accurately, we evaluated the trained CNNs in terms of classification performance, processing time, and the number of data; consequently, we proposed a method to select the most effective CNN.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.4 no.1
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• pp.32-40
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• 2001

Quantifications of fish farm influences on stream water quality may provide basic informations on watershed management to reduce environmental impact due to fish farm development and to conserve stream water quality in forested watershed area. In this research stream water qualities around Mt. Paekun area were monitored seasonally and the following results were obtained. Due to the increase of pH in effluent water from the fish farm it was believed that alkalization of stream water can be accelerated by large scale development of fish farms in the forested watershed area. Negative effects on stream water quality were observed by indications of increase in electrical conductivity and temperature of effluent water from the fish farm. Decreases in physicochemical indices such as the amount of dissolved oxygen, percentage of dissolved oxygen, total amount of cation, total amount of anion and total amount of ion in effluent water from the fish farm were also negative aspects in downstream ecology. It is recommended that water purification system as well as eco-friendly fish farm design should be incorporated to large scale fish farm development plan in forested watershed area.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.2 no.3
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• pp.54-63
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• 1999

Quantifications of fish farm influences on stream water quality may provide basic informations on watershed management to reduce environmental impact due to fish farm development and to conserve stream water quality in forested watershed area. In this research stream water qualities around (Mt.) Paekun area were monitored by seasons and the following results were obtained. Due to the increase of pH in effluent water from the fish farm it was believed that alkalization of stream water can be accelerated by large scale development of fish farms in the forested watershed area. Negative effects on stream water quality was also observed by indications of increase in electrical conductivity and temperature of effluent water from the fish farm. Decreases of physicochemical indexes such as the amount of dissolved oxygen, percentage of dissolved oxygen and total amount of ion in effluent water from the fish farm were also negative aspects in downstream ecology. It is recommended that water purification system as well as eco-friendly fish farm design be incorporated to large scale fish farm development plan in forested watershed area.

• Korean Journal of Ecology and Environment
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• v.53 no.2
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• pp.156-164
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• 2020

The accurate estimation of fish assemblages is highly dependent on the sampling gear used for sampling. We used data from 15 sampling sites along the Nakdong River, which is a large river in South Korea, to identify differences in assemblages and sizes of freshwater fishes collected with either cast nets or gill nets, the two most commonly used sampling gear in South Korea. The two gears differed in the fish assemblages they captured, with more species caught by gill nets. Further, due to its tighter mesh size, the cast net caught significantly smaller fishes than the gill nets(independent t-test, p<0.05). We found the cast net to be appropriate for species that inhabit shallow (less than 2 m) and open water, but inappropriate for deep water, habitats with plant beds, and nocturnal species. Thus, cast net sampling is not efficient in a large river environment, and a combination of sampling methods is more suitable for understanding fish assemblages in such habitats. In general, appropriate selection of fishing methods to specific habitats is necessary to improve data quality and minimize the misrepresentation of environmental conditions.