• 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.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.3
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• pp.181-189
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• 2019

Discarding juvenile fishes under girth 16 cm nearly equal to inner perimeter of codend mesh size collected by a cover net method in bottom trawl. The body size of the main five species (mackerel, horse mackerel, sea bream, melon seed and black throat seaperch) was measured for their body length, girth, weight, height and width and analyzed size selectivity. Frequency of penetrating fish as retention in a cover net was less than 40% of total number of juvenile discarding fish. The most of body length or girth of five species were significantly different between in the codend and in the cover net. The 50% selection girth in the cover net ranged 8-11 cm were smaller than those in the codend ranged 9-13 cm by the species respectively. The 50% selection body length was significantly related with the ratio of body height (H) by body width (W) both for in the codend or in the cover net while 50% selection girth was not significantly related with H/W. Furthermore 50% selection fish size by fish species between in the codend and in the cover net was not significantly different both in body length or girth. Therefore, the girth selectivity represented possibly as one unique value regarding fish body shape was considered as more useful method for multi-species catch in trawl.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.4
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• pp.372-377
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• 2003

Feeding habits of juvenile Liparis tanakai collected from the eelgrass bed in Kwangyang Bay were studied. L. tanakai (2.0-6.0 cm SL) was a carnivore which consumed mainly amphipods (caprellids and gammarids) and caridean shrimps. Its diets also included a large amount of copepods, polychaetes and small fishes. Three distinct ontogenetic feeding groups were noted: (1) the individuals of 2.0-2.5 cm SL preyed heavily on copepods, (2) individuals of 2.5-4.0 cm SL fed mainly on amphipods. (3) individuals over 4.0 cm SL preyed mainly on caridean shrimps and small fishes. The dietary breadth of each size class showed relatively low value, and this means that juvenile L. tanakai depends on only few kinds of food organisms.

• Korean Journal of Ichthyology
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• v.23 no.2
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• pp.135-144
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• 2011

Collections were made monthly using beam trawl from March 2005 to February 2006 in Gujora, and from June 2006 to May 2007 in Geoje Bay to investigate the species composition of Juvenile and Immature Fishes of both coastal areas. Fishes collected in the sandy shore of Gujora were 6 orders, 14 families, 20 species, 224 individuals, and 534.9 g in total. Favonigobius gymnauchen, Trachioncephalus myops, Pseudoblennius percoides, Sagamia geneionema, Repomucenus beniteguri, and Pseudorhombus cinnamoneus were mainly collected. These 6 species accounted for 83.9% of total individuals and 47.1 % of total biomass. On the other hand, fishes collected in Geoje Bay were 4 orders, 8 families, 14 species, 1,406 individuals and 1,899.7 g in total. Acentrogobius pflaumii, Platyce phalusindicus, Chasmichthy dolichognathus, Acanthogobius flavimanus, Gymnogobius urotaenia, and Synechogobius hasta were mainly collected. These 6 species accounted for 97.7% of total individuals and 96% of total biomass. The greatest numbers and biomass of fishes were collected in summer and the lowest in winter. In Geoje Bay, the number of species and individuals reached the peak in September and August, respectively. However, both species and individual numbers were highly fluctuated in Gujora.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.1
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• pp.23-29
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• 2022

This study was carried out to clarify the egg, larvae and juveniles development of Misgurnus anguillicaudatus, and relationships of M. anguillicaudatus and M. mizolepis, Cobitididae Fishes. The adult fishes were collected in Samsan-cheon, Haenam-gun, Jeollanam-do, Korea and their spawning inducement was carried by ovaprim injections. The egg shape was circular and the size was average 1.12 mm. The eggs were hatched at 61 to 72 h after fertilization. The newly hatched larvae had an average 3.23 mm in total length (TL). At 5 days after hatching, the larvae reached to post larval stage and they were 10.3 mm in TL. At 19 days after hatching, it reached to juvenile stage and was 25.3 mm in TL. The egg size of M. anguillicaudatus was almost same as M. mizolepis but the hatching period of M. anguillicaudatus has taken longer. It was possible for interspecific distinguishability of M. anguillicaudatus and M. mizolepis when their larvae reached to juvenile stage by the development of keel-like ridges.

• Journal of Korean Society on Water Environment
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• v.29 no.6
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• pp.746-753
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• 2013

The aim of this study was to evaluate artificial fish shelter, which was known to increase prey survival and expand habitat space to improve species diversity and fish communities in a freshwater ecosystem. The experiment was performed at an outdoor test-bed for three months from 2011 by comparing the responses to adjustments in the volume of the artificial patch (juvenile fish shelter, JFS) in the control and experimental groups. Analysis of the environmental conditions over two periods (Period1 ~ 2) showed minor differences in the physichemical characteristics of water quality, phytoplankton, and zooplankton biomass, thus, allowing comparative analysis of feeding ecology. However, high water temperature conditions in Period1 ($25.6{\pm}2.0^{\circ}C$), affected the predation activity of the piscivorous fishes, Coreoperca herzi (C. herzi, size $89{\pm}4mm$). Survival rates of the prey fishes, Rhynchocypris oxycephalus (R. oxycephalus, size $29{\pm}1mm$), improved as the patch volume increased and were higher than those of the control group by 35.9 ~ 46.7%. Analysis showed that JFS reduced the chances of predator-prey encounter, and thereby minimized prey vulnerability.

• Development and Reproduction
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• v.19 no.1
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• pp.25-31
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• 2015

We have launched an investigation for Embryonic Development, Larvae and Juvenile Morphology, of Buenos aires tetra in order to build basic data of Characidae and fish seeding production. We brought 50 couples of Characidae from Bizidduck aquarium in Yeosu-si, Jeollanamdo, from Korea on March of 2015. We put them in the tetragonal glass aquarium ($50{\times}50{\times}30cm$). Breeding water temperature was $27.5{\sim}28.5^{\circ}C$ (mean $28.0{\pm}0.05^{\circ}C$) and being maintained. The shape of fertilized egg was round shape, and it was adhesive demersal egg. The egg size was 0.63~0.91 mm (mean $0.74{\pm}0.07mm$, n=20). After getting fertilized egg, the developmental stage was gastrula stage, and embryo covered almost two-thirds of Yolk. Incubation was happened after 16 hours 13 minutes from gastrula stage, and the tail of juvenile came out first with tearing egg capsule. Immediately after the incubation, prelarvae had 3.78~3.88 mm length (mean $3.84{\pm}0.04mm$, n=5), and it had no mouth and anus yet. 34 days after hatching from the incubation, juvenile had 8.63~13.1 mm (mean $10.9{\pm}1.66mm$), and it had similar silver-colored body shape with its mother.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2003.05a
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• pp.158-159
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• 2003

Although the sub-chronic toxic effects of metal on fishes are well documented, that is mostly in fishes exposed to waterborne metal but few studied have been conducted on the effects of dietary metal (Handy, 1996). The realization that dietary uptake of metal is a major cause of long-term contamination in wild fish has renewed interest in the nutritional and toxicological effects of metal in the food of fishes (Handy, 1996). (omitted)

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.50 no.3
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• pp.334-341
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• 2014

The diet composition of juvenile Korean piscivorous chub, Opsariichthys uncirostris amurensis were studied using 277 specimens collected from January to December 2004 in the surf zone of Nakdong river estuary. The size of Opsariichthys uncirostris amurensis ranged from 2.6 to 9.1 cm in standard length (SL). Opsariichthys uncirostris amurensis was carnivore that consumes mainly amphipods and insects. Its diet also included small quantities of polychaetes, fishes, and algae and plants. Opsariichthys uncirostris amurensis showed ontogenetic diet change. Smaller individuals (< 4 cm SL) mainly consumed amphipods. The portion of these prey items decreased with increasing fish size, and this decrease was paralleled with increased consumption of larger preys such as polychaetes and fishes. Insects were preyed moderated values in all size classes. Opsariichthys uncirostris amurensis diet also showed diel change with consuming more on amphipods and polychaetes during day.

• Fisheries and Aquatic Sciences
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• v.18 no.3
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• pp.325-332
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• 2015

An active stimulating method for juvenile fishes to drive escaping from mesh of the codend was examined by shaking canvas in the bottom trawl followed by shrimp beam trawl. Field fishing trials by a bottom trawl were carried out between the Geomoondo and Jejudo in west of South sea, Korea by conver-net methods to examine the effect on the reduction of juvenile fish as a discard catch by generating a shaking movement of the codend using two pieces of asymmetrical semi-circular canvas. The mean period of the shaking motion with the round canvas was 10-15 s, and the range of amplitude as a vertical depth change was up to 0.4-0.6 m when towing speed 3.4-4.3 k't as estimated by peak event analysis. The escape rate of juvenile fish in conver-net by total juvenile bycatch (codend and cover-net) in 14 trials increased from 20% in a steady codend to 34% using a shaking codend in the bottom trawl, while the marketing catch or total bycatch was similar between steady and shaking cod ends. There was no difference in the body size of the fish and species composition between the steady and shaking cod ends. Above results demonstrate a new method for bycatch reduction actually up to 18% using an active stimulating device, although further experiments are needed to increase an effective shaking motion of the codend in amplitude and period for more bycatch reduction.