• 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 Ecology and Environment
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• v.56 no.4
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• pp.406-413
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• 2023

Captive breeding and reintroduction are crucial strategies for conserving endangered species populations. However, fish raised in predator-free environments, show a lack of recognition of predationrelated stimuli such as chemical and visual signals. It is critical to recognize chemical signals from injured conspecifics, also known as alarm signals, and the order or shape of predators to indicate the spread of predation risk in the habitat. We conducted a laboratory experiment to determine and adjust the optimal exposure period to induce appropriate anti-predator behavior response to different types of stimuli (Chemical, Visual and Chemical+Visual) for the endangered species Microphysogobio rapidus. Our results demonstrate that predator avoidance behavior varies depending on the types of stimuli and the duration of predation risk exposure. First, the results showed captive-breed M. rapidus show lack of response against conspecific alarm signal (Chemical cue) before the predation risk exposure period and tend to increase response over predation risk exposure time. Second, response to predator (visual cue) tend to peak at 48 hours cumulative exposure, but show dramatic decrease after 72 hours cumulative exposure. Finally, response to the mixed cue (Chemical+visual) tend to peak prior to the predation risk exposure period and show reduced response during subsequent exposure periods. This experiment confirms the lack of responsiveness to conspecific alarm signals in captive-bred M. rapidus and the need for an optimal nature behavior enhancement program prior to release of endangered species. Furthermore, responsiveness to predator visual signal peak at 48 hours cumulative exposure, suggest an optimal predation risk exposure period of up to 48 hours.

• Korean Journal of Ecology and Environment
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• v.37 no.1 s.106
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• pp.130-136
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• 2004

In the present study, prey preference of juvenile fishes was examined using an experimental approach. Zooplankton composition, as a prey of the fish, was evaluated by taking into account the species as well as body size of juveniles in the aquarium. The predation of juvenile fishes is known to be an important factor in changes of zooplankton communities. In some previous studies at the regulated Nakdong River, the collapse of large cladcoerans and an increase in the rotifer population by selective predation during spring and summer were observed. This study focused on the predation of juvenile fishes such as Hyporhamphus sajori, Rhinogobius brunneus, and Opsariichtys uncirostris amurensis on zooplankton community structure in mesocosm scale experiments. These fishes selected the cladoceran Moina micrura with highest individual preference value (Manly/Chesson index)among zooplankton prey in the experimental aquarium. When the size-selective prey preferences of the juvenile fish were compared, both small (body size <2 cm) and large (body size >2cm) juveniles of O. uncirostris positively selected M. micrura. In the outdoor experimental tanks, juvenile fishes consumed the cladoceran M. micrura, resulting in an high abundance of the rotifer, Polyarthra spp. The results suggest that juvenile fish predation may play an important role in regulating the zooplankton community structure by reducing the cladoceran density and increase of rotifers in the Nakdong River during spring and summer.

• Korean Journal of Ecology and Environment
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• v.43 no.4
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• pp.513-517
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• 2010

The diel swarming of Moina macrocopa and the relationship between environmental factors were evaluated in a shallow reservoir. The littoral density of Moina macrocopa maintained low from night to noon, reached maximum density at the afternoon with compact swarms at the waters' edge, and dispersed after sunset. The recruitment of Moina macrocopa and changes of water temperature (r=0.709, p<0.001) and juvenile fish density (r=0.511, p=0.002) in the littoral zone showed a significant positive relationships. After the induction of diel horizontal migration toward littoral zone, therefore, direct juvenile fish predation pressure should be induced Moina macrocopa swarming.

• Journal of Korean Society on Water Environment
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• v.27 no.6
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• pp.776-783
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• 2011

In a natural water body, a useful ecotechnology to reduce standing crops of phytoplankton is to strengthen the top-down force of zooplankton. However, the predation of fish for zooplankton can make the force weak. This study was conducted to find out the effect of fish on the grazing pressure of zooplankton in the mesocosms established in a eutrophic stream (Kyongan Stream) from October to November in 2010. In the corral with fish, chlorophyll a concentration increased, and a small size cladoceran Bosmina longirostris was dominant. In the corral without fish, chlorophyll a concentration decreased along with the domination of a large cladoceran Daphnia galeata and a large copepod Eudiaptomus japonicus. The size-selective predation of fish appeared to miniaturize the zooplankton community, to narrow their food-size spectrum, and to weaken the top-down force.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.456-457
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• 2005

• Korean Journal of Ecology and Environment
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• v.42 no.1
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• pp.107-114
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• 2009

We investigated the predation behavior of larval damselfly on Daphnia pulex and D. galeata, and compared the life history and morphological defenses in two Daphnia species against larval damselfly and fish kairomones. Larval damselflies showed size-dependent predation behavior and preyed upon smaller daphnids easily regardless light condition. Overall, small D. galeata juveniles were more vulnerable than D. pulex to the larval damselfly predation. D. pulex displayed life history and morphological changes as the anti-predator defenses against larval damselfly as well as large mouth bass, while D. galeata showed the anti-predator defenses to the large mouth bass. Thus, our results revealed that two Daphnia species exhibits different anti-predator defense strategy to increase survivorship.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.9 no.1
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• pp.40-49
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• 2004

An ecological study on a sea urchin population, Strongylocentrotus nudus, a key role species in recovery of macroalgal bed, was conducted in Hosan, Samcheok area on the east coast of Korea. Three experimental plots, namely, AMB (artificially-restored macroalgal bed), BG (barren grounds) and NMB (natural macroalgal bed) were established after a pilot survey in June 2002. Distribution and abundance, grazing rates, predation pressure and predator guilds on S. nudus were estimated in three plots bimonthly from Aug. to Dec., 2002. Abundance of S. nudus was lowest, but median test diameter of the urchin was highest (Kruskal-Wallis test, p-value, p<0.001 in Aug. and p=0.003 in Oct.) in NMB In-situ grazing rate of S. nudus estimated by enclosure cage experiment in NMB was about 12 times higher in Aug. (160.0 mg seaweed/g sea urchin/day) than in Oct. (13.8). Predation intensity measured by tethering experiment was higher in NMB. Most of the predators on S. nudus were invertebrates and no fish predators were found. Predator guilds identified by the fish trap experiment using live or dead sea urchins included who]ks Neptunea arthritica, starfish Asterina pectinifera, hermit crabs Pagurus of. samuelis, Paguristes barbatus, brown shawl crabs Atergatis integerrimus and crabs Actaea subglobosa. High predation pressure on S. nudus in natural macroalgal beds was the likely cause of its low density. Elevated sea urchin density and the consequent lasting deforestation of macroalgae in barren grounds demonstrate the importance of predation pressure on sea urchins.

• Korean Journal of Environmental Biology
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• v.31 no.4
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• pp.370-375
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• 2013

Exotic species in aquatic ecosystem generate various problems domestically as well as globally. Largemouth bass (Micropterus salmoides) which is a well-known exotic species globally, acts as a substantial disturbance factor on the native fish communities in Korea due to the high predation pressure and hence designated as a ecologically harmful species by Ministry of Environment. In this study, we investigated the impact of largemouth bass on Korean native fish population, crucian carp (Carassius auratus), to identify responses of the prey fish. Two fish species were collected at seven reservoirs distributed at the Nakdong River catchment area, and changes in length-frequency and length-weight relationship (LWR) were analysed depending on existence of large-mouth bass. At bass absent sites, ratio of under age 1 year individuals were small, and over age two years were dominant. Conversely, normal length-frequency distribution pattern was identified at bass absent sites. The LWR of crucian carp (fish smaller than total length of 160 mm were only considered as it is frequently consumed by bass predation) was different depending upon bass existence. The value of parameter b at bass absent reservoirs was 2.909, which was smaller than that of bass present reservoirs, 3.100. Our results imply that crucian carp at bass present reservoirs presented a different strategy to survive from predation by bass, through relatively rapid growth. We propose that other native species might have similar growth strategies like crucian carp.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.20 no.1
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• pp.36-42
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• 2015

To determine the predation rate of threadsail filefish, we conducted feeding experiment of threadsail filefish, Stephanolepis cirrhifer on different life stages (medusae, ephyrae, and polyps) of Aurelia aurita s.l. in the laboratory. All size groups of threadsail filefish actively preyed on moon jellyfish Aurelia aurita s.l. and predation rate was proportional to the wet weight of threadsail filefish. Average wet weight 0.5, 1, 2.2 g of threadsail filefish preyed on average $0.77{\pm}0.51g\;fish^{-1}h^{-1}$ of medusae. Average wet weight 150 and 344 g of threadsail filefish preyed on $9.26{\pm}1.61$ and $15.89{\pm}3.67g\;fish^{-1}h^{-1}$ of medusae respectively. In ephyrae and polyps, average wet weight 3.7 g of juvenile of threadsail filefish preyed on 100 ephyrae within 10 minutes and average wet weight 2.2 g of juvenile of threadsail filefish preyed on $5.73{\pm}0.59$ polyps $g^{-1}$ of fish $h^{-1}$. Whereas adults of threadsail filefish did not prey on polyps. In feeding preference experiments to elucidate whether threadsail filefish prey on moon jellyfish in the sea, adults of threadsail filefish preyed on mostly oysters (ca. 60%) and polychaetes (ca. 80%). Medusae were consumed only 2% of total. However, juvenile of threadsail filefish preyed on ephyrae and polyps as well as mysid shrimps. Besides, polyps were consistently consumed during the experiment. Although juvenile of threadsail filefish consumed all kinds of prey, they ceased feeding at temperatures below $11^{\circ}C$, which suggests that possibility of predation on ephyrae may be very low in the sea because ephyrae are released at low temperatures below $11^{\circ}C$ from March to April. Whereas polyps are inhabitable in all seasons in Korean coastal waters, juvenile of threadsail filefish may prey on polyps in the sea. These results suggest that removing moon jellyfish at polyp stage by using juvenile of threadsail filefish is the most effective way for extermination of moon jellyfish.