• Korean Journal of Ichthyology
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• v.21 no.3
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• pp.200-207
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• 2009

The feeding habits of Micropterus salmoides were investigated and two lakes, Lake Okjeong and Lake Yongdam, between March 2007 and March 2009. In Lake Okjeong, M. salmoides was likely introduced almost 20 years ago and in Lake Yongdam was less than 10 years ago. Food contents in M. salmoides from each lakes showed a significant difference in Index of Relative Importance (IRI) value. Fishes was most important prey item in Lake Okjeong whereas decapoda in Lake Yongdam. The difference in IRI of the Decapoda means that their abundance of this prey item in Lake Yongdam is higher than in Lake Okjeong. These decrease of the Decapoda in the lake may be caused by the feeding of M. salmoides. In Lake Yongdam the proportion of the Decapoda in the food of M. salmoides decreased during the study period, while the fishes increased from 2007 to 2008, suggesting related relationship to the feeding activity of M. salmoides as was seen in Lake Okjeong.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.15 no.4
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• pp.333-344
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• 1982

Major species of zooplankters were idcentified from the specimens collected from Lake Ok-Jeong for 1 year period and the descriptions are given together with the list of tile species and some drawings. Assuming from the dominant species present in the lake, the Lake Ok-Jeong is considered to be a fairly progressed eutrophlc lake. For a few species, some Questions are presented in taxonomical and biogeographical view points.

• Korean Journal of Ichthyology
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• v.19 no.2
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• pp.142-153
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• 2007

Fertilized eggs of Plecoglossus altivelis over than 1,000,000 were introduced into Okjeong, Jeollabuk-do, Korea by K-water, 2001. Since then, this lake and the neighbouring tributaries gave sufficient habitat to maintain their life cycle which are being the land-locked. A land-locked ayu of annual life is ascending and descending from Lake Okjeong to streams for spawning and growth. Among the streams, the Churyeong stream reaching about 32 km in length is a major site for growth and spawning. But the land-locked ayu was no longer seen in the upper regions of the Churyeong stream over than about 12 km distance from Lake Okjeong. Because there were 11 weirs along with the Churyeong stream, it was difficult for them to move freely up to upper regions, and it causes irregular growth condition although they must be actively growing with feeding for spawning. During three survey years (2004 to 2006), in lowest rainfall-recorded 2005, the ayu population was not able to move up actively across the weirs and just stayed around the weirs, and finally it let them grow slowly and unstably. Also although there are 11 weirs, only 3 fish ways existed. Such environmental factors will seriously affect growth, spawning and size of ayu population in this area.

• River and Culture
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• v.2 no.4
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• pp.69-73
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• 2006

• Korean Journal of Ichthyology
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• v.20 no.1
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• pp.36-44
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• 2008

Feeding habits of Micropterus salmoides were investigated from the stomach contents of specimens ranging from 13 to 511 mm in standard length (n = 419), which are collected in the Lake Okjeong, Korea, 2006 to 2007. M. salmoides is a very strong carnivorous fish eating living organisms such as lots of fishes, small amount of aquatic insects and shrimps. As they grow, the feeding habits changed : they fed mainly on Branchioda in 10 to 20 mm in SL., aquatic insects and small fishes in 30 to 50 mm in SL., fishes including Zacco platypus, Hemiculter eigenmanni and Rhinogobius brunneus over 50 mm. However, among the prey organisms, M. salmoides most preferred living fishes. Analysing ichthyofauna of the Lake Okjeong from 1981 to the present investigation, after and before introduction of M. salmoides, it was showed that there was a certain reduction in fish diversity. Consequently, it is likely to let the strongly fish-eating habit to reduce a diversity of native fishes in the lake.

• 한국생태학회:학술대회논문집
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• 1999.05a
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• pp.127.1-127.1
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• 1999

• Korean Journal of Ichthyology
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• v.19 no.1
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• pp.24-34
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• 2007

After releasing more than 1,000,000 fertilized eggs of Plecoglossus altivelis into Lake Okjeong, Jeollabuk-do, on October, 2001 by KOWACO, they seem to be land-locked. Study on the distribution and ecology of a land-locked ayu, P. altivelis, was performed from Lake Okjeong to upper streams as Jowon, Churyeong, Oknyedong where consisted of rocky bottom with fast current freshwater system during April to October. The hatched larva and juveniles descended from streams to Lake Okjeong and inhabit Lake Okjeong from November to next March. The sex ratio of female to male was 1 : 2.70, and the size in standard length of females and males was similar, in $90{\sim}220(142{\pm}29.3)mm$. During the middle September to the middle October, they laid eggs on the pebbly bottom of the rapids which are $20{\sim}22^{\circ}C$ in water temperature and 30~70 cm in depth. The number of full-grown eggs was greatly various from 14,283~91,500.

• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.487-497
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• 2001

Investigated data on Lake Okjeong were used for the simulation of water quality. According to the simulation results, the effective scheme of water quality management on reservoir has been proposed. It has been recognized that the water quality of Lake Okjeong is under eutrophic and mesotrophic condition even though there are seasonal variation. The water quality of lake is mainly affected by the inflow of pollutant load from watershed. Therefore, to estimate and quantify the accurate amounts of pollutants flowing into reservoir is absolutely necessary for the effective management of water quality on Lake Okjeong. When the pollutant load measured during 7 different rainy periods in 1999 was compared with total pollutant load in 1999. TN and TP measured during 7 different rainy periods showed almost 50% of total pollutant load. In case of SS, it was 72.8%. On the other hand, the rainfall amount measured during the 7 different rainy periods was about 17.5% of total rainfall amount in 1999. Release rate of TP shows 11.92 mg/L at fish farm site and 0.2∼1.9 mg/L at monitoring station of water quality on Lake Okjeong, and which is considered to be less than that of other foreign reservoirs under the circumstances of anoxic condition. For the effective management of water quality on Lake Okjeong. WASP5 water quality simulation model has been applied and verified, and the verified model was used to propose the effective scheme of water quality management. In this case, 6 different scenarios were applied, by changing the amount of inflow of pollutant load in each subbasin. The most effective scheme has turned out that pollutant load generated from Imsil and Gwanchon subbasin should be reduced, and the best way to improve the water a quality is to reduce the pollutant load at every subbasin. According to the simulation result, wastewater treatment facility should be located at every subbasin.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.19 no.1
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• pp.67-71
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• 1986

Concentration of dissolved $vitamin\;B_{12}$ in the water of Okjeong lake have been determined by microbiological assay methods on the 20th of August, 1983. Also the relations between the $vitamin\;B_{12}$ and other physical, chemical and biological environmental factors were investigated. $Vitamin\;B_{12}$ was assayed with Euglena gracilis Z strain. The results obtained in this investigation were as follows : 1. Generally, the values of COD and $Cl^-$ were higher than values reported in 1981. 2. The concentration of nutrient salts in the lake water was found to be at a higher level: above the general criterion in a eutrophic lake viz., phosphorous 0.175-0.225 mg/l. 3. Chlorophyll a contents in this lake were $1.1-8.7{\mu}g/l$, 4. The concentration of $vitamin\;B_{12}$ in the water fairly high: 1.25-6.0 ng. It is apparent that concentrations of the $vitamin\;B_{12}$ as well as nutrient salts were high in the water of Okjeong lake. It was found that Okjeong lake was in eutrophic.

• Korean Journal of Ecology and Environment
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• v.35 no.2 s.98
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• pp.79-91
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• 2002

A time variable modeling study was performed for seasonal variations of vertical temperature profiles in the Okjung Lake located in upstream of the Sumjin River. Based on the model structure of the US Army Corps of Engineer's CE-QUAL-W2, the lake was divided into 3 branches, 50 longitudinal segments and 49 vertical layers and vertical profiles of water temperature and current velocity were simulated over one year. The model results were calibrated and verified against vertical profiles of water temperature measured every month from March 1998 to February 1999 at 5 different locations. The model results showed a good agreement with the field measurements. The hydrologic balance during this period was validated by comparing the simulated values of surface elevation level with the measured data. There was some discrepancy in July data between the model results and the fleld measurements. This could be attributed partially to the inadequacy of the model to the highly hydrodynamic nature of water body and partially to the lack of accuracy in local atmospheric temperature data during summer monsoon period. The model results have shown that there was no seasonal over-turn in most part of the Okjung Lake, where water temperature maintained above $4^{\circ}C$ over one year. In the upstream shal-low area (depth<20 meter), however, temperature at surface layer fell below $4^{\circ}C$ and water was frozen such that slight over-turn would occur during winter period. From this study, we concluded that the Okjung Lake is oligomictic. This conclusionis significantly different from the general pattern that the lakes located from $20^{\circ}C$ to $40^{\circ}C$ latitude would be warm monomictic. From the examination of simulated current velocity distribution, it was found that the upstream inflows would infiltrate into mesolimnion of the lake during hydrodynamic summer monsoon periods due to the thermal density of water.