• Journal of Fisheries and Marine Sciences Education
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• v.26 no.1
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• pp.72-80
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• 2014

Oxygen consumption (OC) of male black porgy Acanthopagrus schlegelii reared in freshwater (BFW) and seawater (BSW) during the reproductive period was $165.4{\pm}11.0$, $77.6{\pm}8.0$ mg $O_2/kg/h$ at $15^{\circ}C$, $186.2{\pm}13.1$, $133.4{\pm}6.7$ mg $O_2/kg/h$ at $20^{\circ}C$ and $267.9{\pm}19.1$, $198.6{\pm}8.3$ mg $O_2/kg/h$ at $25^{\circ}C$, respectively. During the non-reproductive period, it was shown as $174.0{\pm}7.0$, $85.6{\pm}5.5$ mg $O_2/kg/h$ at $15^{\circ}C$, $200.6{\pm}11.1$, $119.2{\pm}8.7$ mg $O_2/kg/h$ at $20^{\circ}C$ and $271.1{\pm}7.5$, $194.7{\pm}16.7$ mg $O_2/kg/h$ at $25^{\circ}C$, respectively. Thus, OC of BFW was higher than BSW both for non-reproductive and reproductive period. Also, OC increased in proportion to the rise in water temperature, and there was no difference of OC between BFW and BSW at each water temperature during the reproductive or non-reproductive period. OC of BFW and BSW showed clear circadian rhythms on photic conditions of reproductive and non-reproductive period, and the fish consumed more oxygen during the dark phase than for the light phase. In particular, OC of BFW during the reproductive period increased more sharply compared to non-reproductive period when the increase of water temperature was accompanied by the shift from dark to light phase. This implies that they react to the light more sensitively for reproductive period than for non-reproductive period.

• Journal of Life Science
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• v.25 no.5
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• pp.568-576
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• 2015

The marine microalga Pavlova viridis can grow fast and has the ability to accumulate essential nutrients for culturing marine animals, such as EPA and DHA, and it has been used as food for raring larval fish and prawn. The symbiotic relationship between the flagellate microalga Pavlova viridis and its associated bacteria was investigated. An axenic culture of P. viridis was obtained by repeated treatment of the microalga with an antibiotic cocktail. The axenic status was confirmed after sub-culturing three times in a sterile f/2 medium without an antibiotic. The axenic alga was then co-inoculated with five bacteria, arbitrarily designated as I1–I5, isolated from the alga to test the growth promotion of the algae. All bacterial strains promoted the growth of P. viridis, and bacterial isolate I3 was the most effective among the five bacteria tested. The cell number of P. viridis in the co-culture with I3 was significantly higher than that of the control culture. A sequence analysis of the 16S rRNA gene isolated from I3 revealed a 97% nucleotide sequence similarity to that of Citrobacter sp. The growth of strain I3 was also significantly enhanced by co-culturing with P. viridis, indicating a symbiotic relationship between the microalga and its associated bacterium. The association between the microalga and bacterium was confirmed by scanning electron microscopy.

• Fisheries and Aquatic Sciences
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• v.9 no.4
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• pp.160-166
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• 2006

We explored the possibilities of using the freshwater rotifer Brachionus angularis as a live food for small fishes cultured in fresh- or brackish waters. Brachionus angularis were collected from a reservoir for isolation and laboratory culture. Length and width of the lorica were $102.3{\mu}m$ and $76.6{\mu}m$, respectively, and those of amictic eggs were $64.4{\mu}m\;and\;47.9{\mu}m$, respectively. When their growth rates were examined at six different temperatures, i.e., 15, 20, 25, 30, 35, and $40^{\circ}C$, the highest daily growth rate of 0.801 was observed at $35^{\circ}C$, and growth was lower with decreasing temperature. Adaptation to salinity change was evaluated with two different modes of salinity increase: step-wise elevation lasting for short durations of 5 to 30 min or a long duration of 24 h. With the short duration modes, no individuals survived salinity higher than 10 psu, and the number of live individuals did not increase throughout the experiment. However, in the 24-h elevation, the number of individuals increased when salinity was elevated by 1 to 2 psu per day for the first 2 or 3 days, while no increase in number occurred at salinity increments higher than 3 psu per day. In addition, to assess the effect of different diets, four single-component diets (Chlorella vulgaris, Nannochloris sp., baker's yeast, or dry yeast) and three combination diets (C. vulgaris + Nannochloris sp. + baker's yeast + dry yeast; C. vulgaris 70% + baker's yeast 30%; C. vulgaris 30% + baker's yeast 70%) were used. The specific growth rates of B. angularis fed combination diets were higher than those of rotifers fed any single-component diet, with the highest rate of 0.648 in B. angularis fed a mixture of C. vulgaris, Nannochloris sp., baker's yeast, and dry yeast, and the lowest rate of 0.200 in those fed dry yeast only. Our results indicate that the freshwater rotifer B. angularis can be used for seedling production of both freshwater and brackish-water fishes that require small (less than about $120{\mu}m$) live food during their early stages.

• Korean Journal of Ichthyology
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• v.32 no.3
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• pp.148-159
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• 2020

This study investigated the seasonal and inter-annual changes in vertical distribution and size spectrum of walleye pollock, Gadus chalcogrammus inhabiting middle eastern coast of Korea (hear after pollock). Pollock was distributed between 50 m and 600 m depth range, and body size (total length) ranged from 16.6 cm to 81.5 cm. The trends of population body size were increased in autumn and winter and decreased in spring and summer. Vertical distribution of pollock showned depth-dependent patterns with distributing smaller individuals mainly in the upper layer (shallower depth), while larger fish in deeper habitats. Those patterns in vertical distribution of pollock population is probably due to be the results of energy-saving strategy, metabolic effects, and changes in prey selections according to pollock growth, derived from spatial and temporal changes in oceanic condition in habitat grounds. When water temperature in upper layer were increased and that of below thermocline depth became decreased in 2017, the ratio of smaller (<35 cm) and larger (≥35 cm) individuals was biased toward larger fishes, extending their distribution into shallow depth, and consequently main fishing ground was formed in far from coastal area. In addition, the ratio of smaller individual distributing between 100~300 m was increased with decreasing temperature gradient between below thermocline and bottom layer. Changes in spatial and temporal distributions of pollock population likely be related with vertical and horizontal changes in oceanic conditions and, consequently food supplies.

• Journal of Aquaculture
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• v.19 no.3
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• pp.149-156
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• 2006

Stress responses, osmoregulation and growth of black porgy reared in freshwater or seawater were investigated by supplying the feed (10 mg/kg feed) treated with the $T_3$ (3,5,3'-triiodo-L-thyronine) for 90 days. Plasma $T_3$ in black porgy reared for 60 days in freshwater with (FT) or without (FN) $T_3$, treatment was lower than that in black porgy reared in seawater with (ST) or without (SN) $T_3$ treatment. The concentration of $T_3$ in FT was significantly more than that in FN. Plasma cortisol in FT, at the same day, was 4 times higher than that in FN, whereas the differences of the hormone between ST and SN was not significant. Although the levels of plasma glucose in FN and FT tended to be lower than that in ST and SN, no differences were found between fish reared in freshwater and seawater after $T_3$ treatment. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of black porgy reared in seawater showed no difference throughout the experimental period. However, at the beginning stages of the experiment, the plasma levels of these enzymes in FN and FT were higher than in SN and ST. Recovering of AST level to the level of SN or FT was laster in FT than in FN. However, no effects of the exogenous $T_3$ treatment on osmoregulatory capacity and growth of black porgy reared in freshwater or seawater were observed in this study.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.2
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• pp.67-83
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• 2012

In order to evaluate die geochemical characteristics of sediment in a semi-enclosed bay used as shellfish and fish farming area, the concentrations of metallic(V, Cr, Mn, Fe, Co. Ni, Cu, Zn, Ag, Cd, Hg, Ph, As) and non-metallic(P, Se) elements and uranium were measured in the surface sediment samples collected from 19 stations of Gamak Bay in April 2010. Metal contamination status in the sediments were also evaluated using the sediment quality guidelines(SQGs) proposed by the National Oceanic and Atmospheric Administration(NOAA) and the enrichment factor(EF). The concentrations of elements in sediment were mainly controlled by quartz-dilution effect(V, Cr, Fe, Co and Ni), the dilution effect of organic matter(Cd and U), and metal redistribution by the decomposition of organic matter(Mn, Ag, As, and Se). The concentrations of metals, except As and Ni, in sediments from all sampling stations were lower than ERL values of NOAA. Conclusively, the surface sediment of Gamak Bay was slightly polluted with Ni, Ag, Cd, and Cd but was not polluted with other elements on the basis of EF results. Our results suggest that the surface sediment in Gamak Bay is not polluted by metallic elements.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.1
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• pp.1-13
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• 2012

We measured various geochemical parameters, including the grain size, loss on ignition(LOI), total organic carbon(TOC), total nitrogen(TN), total sulfur(TS) and metallic elements, in surface sediment collected from 19 stations in Gamak Bay in April 2010 in order to understand the sedimentary types, the origin of organic matters, and the distribution patterns of alkali(Li, Na, K, Rb) and alkaline earth(Be, Mg, Ca, Sr, Ba) elements. The surface sediments were mainly composed of mud. The concentrations of Chlorophyll-a, TOC, TN, TS and LOI in sediment were the highest at the cultivation areas of fish and shellfish in the northern and southern parts of the bay. The redox potential(or oxidation-reduction potential) showed the positive value in the middle part of the bay, indicating that the surface sediment is under oxidized condition. The organic materials in sediment at almost all of stations were characterized by the autochthonous origin. Based on the overall distributions of metallic elements, it appears that the concentrations of alkali and alkaline earth elements except Ba in sediment are mainly influenced by the dilution effect of quartz. The concentrations of Sr and Ba are also dependent on the secondary factors such as the effect of calcium carbonate and the redox potential.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.1
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• pp.9-16
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• 2013

The growth and production of Aulichthys japonicus (6.70~15.32 cm TL) were investigated in an eelgrass bed of Dongdae Bay, Korea throughout 2006. A total 888 A. japonicus were collected with a small beam trawl. Growth in fish total length was expressed by the von Bertalanffy's growth equation as: $L_t=24.8257(1-e^{-0.5583(t+0.4816)})$. The densities, biomass, daily, annual production, and P/B ratio were $0.01{\pm}0.009/m^{-2}$, $0.17{\pm}0.16g/m^2$, $0.00006{\pm}0.00006g$ AFDW/$m^2$/day, 0.02g AFDW/$m^2$/yr, and 0.12, respectively. Monthly variation in production of A. japonicus was large; the peak occurred at July, September and November 2006 (0.000182, 0.000127 and 0.000123 g AFDW/$m^2$/day), where as the lowest value was 0.000003g AFDW/$m^2$/day at April and May 2006. Monthly change in production of A. japonicus was positive correlated with number of individuals, biomass and growth rate.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.672-677
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• 2001

There was an outbreak of food poisoning due to eating well-cooked imported tropical fish, Stromateus stellatus on May, 2000, in Korea. Gastrointestinal symptoms such as diarrhea ($92\%$), nausea ($77\%$), abdominal pain ($54\%$), vomiting ($46\%$) and headache ($23\%$) were experienced within $0.5\~2$ hours (median 1 hour) after eating, Any specific natural toxins were not confirmed concerned to those poisoning, but large amount of abnormal lipid ($23\%$) was found from the muscle such as 1-O-diacyl glyceryl ethers (DAGE), which was consisted of $61.8\%$ of total lipid. The 16:0 ($66.3\%$) and 18:1 ($15.8\%$) alkyl chains were dominant in all alkyl chains of DAGE which were presumed as the causative agent for the diarrheal food poisoning. O1eic acid (18:1) was found as a major fatty acid at the sn-2 or 3 in DAGEs. O-16:0-18:1-18:1 ($16.2\%$),O-16:0-18:1-22:1 ($14.7\%$) and O-18:0-18:1-22:1 ($11.0\%$) were contained as the major molecular species of DAGEs by RI-HPLC.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.4
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• pp.1006-1013
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• 2016

The observed external injury, movement and survival rate according to storage and recovery of the juvenile sea cucumber, Apostichopus japonicus(wet weight $1.0{\pm}0.2g$). The investigated application possibility of external injury(grade I~IV) and movement variation(buccal tentacle, motion, obversion, movement) for estimate of survival rate. The survival rate was observed through the recovery after storage of the sea cucumber in various water temperature(10, 15, 20, $25^{\circ}C$) and hours(3, 6, 12, 24 hour). Grade of external injury lower in the 24 hour experiment group of $20^{\circ}C$ water temperature and 12 hour experiment group of $25^{\circ}C$ water temperature. Buccal tentacle and movement strong related survival rate and external injury. In the case of $20^{\circ}C$ water temperature, survival rate was observed decrease 24 hours experiment. $25^{\circ}C$ water temperature was high to 6 hours but 12 hours experiment group observed decrease of the survival rate. The lethal time(LT10) of the juvenile sea cucumber was 15.73 hours($20^{\circ}C$) and 5.57 hours($25^{\circ}C$). The results of this study provided various measurement method of survival rate according to transportation of the juvenile sea cucumber for release.