• Journal of fish pathology
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• v.27 no.1
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• pp.57-65
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• 2014

Copper ($CuSO_4$) has been widely used to control algae and pathogens in fish culture ponds. However, its toxic effects on fish depend not only on its concentration in water but also on water quality. The susceptibility of the rockfish, Sebastes schlegeli to copper was evaluated at three water-temperatures (WT; 18, 23 and $28^{\circ}C$) for 4 days. After the exposure of two copper concentrations (100 and $200{\mu}g/L$), a hematological effect was exerted on rockfish, by causing changes in red blood cell count and hematocrit value at $28^{\circ}C$. Total protein levels of the fish showed a tendency of co-increase with glucose depend on the WT, after copper exposure. However, the plasma calcium and magnesium levels were significantly increased at $200{\mu}g/L$ copper, regardless of the WT. Enzymes activities including ALT and LDH in serum were also significantly increased depend upon the copper treatment only. This indicates that inorganic components and enzymes activities were sensitive indexes to stress by toxicant such as copper. The cortisol levels were significantly elevated by both WT rising and copper treatment in serum of rock fish. In conclusion, these changes can be seen as an initial response to temperature stress and as a sustaining response to copper exposure. The present findings suggest that a simultaneous stress by temperature change and copper exposure could accelerate an alteration of hematological and plasma biological parameters in the rockfish.

• Development and Reproduction
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• v.16 no.2
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• pp.101-106
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• 2012

Importance of behavior factors or environmental factors in visual organization and visual function of fish is treated with great care in visual ecology, and there is no study about initial ocular growth and development on the dark banded rockfish, Sebastes inermis. Thus, this study was performed. The total length, head length, head depth, eye diameter and lens diameter of the dark banded rockfish showed positive allometric relationship between parturition stage and 60 days post-parturition (dpp). The increase in total length relative to head length and head depth, head length growth relative to eye diameter and lens diameter, and head depth growth relative to eye and lens diameter were nearly isometric. The eyes were formed completely at parturtion stage. At this age, the eye has an optic nerve fiber layer, a ganglion cell layer, an inner plexiform layer, an inner nuclear layer, an outer plexiform layer, an outer nuclear layer, an outer limiting membrane, a rod and cone layer and an epithelial layer. Thickness of retina at 60 dpp was higher than that of at parturition stage. During this experiment, the proportion of the rod and cone layer, outer nuclear layer, and optic nerve fiber layer of retina were significantly increased, while the proportion of the outer plexiform layer, inner nuclear layer and ganglion cell layer of retina were significantly decreased (P<0.05). The essential demands that must be met by the retina in this species pertain to light sensitivity and spatial resolution.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.39 no.3
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• pp.297-302
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• 2006

We investigated gonadal development and sex ratio of artificial seedlings of the oblong rockfish Sebastes oblongus, based on samplings for 370 days just after parturition. The primordial germ cells and genital ridge appeared separately under the mesentery in the yolk-sac stage larva (total length: 7.10-7.77 mm) just after parturition. The primordial germ cells and genital ridge integrated to form primordial gonad in 5-day-old larvae (7.12-9.68 mm), and then proliferation of somatic cell and germ cell occurred in the gonad, which was maintained undifferentiated until 45-days after parturition (18.6-20.4 mm). The ovarian differentiation began in the larva of 50-days old (dab) after parturition (dap) (20.0-24.5 mm). The somatic tissues elongated from the both opposite end-sites of undifferentiated gonad were consequently fused and formed a complete ovarian cavity at 60-days old dap (25.5-32.0 mm). In 80-days old dap (37.3-47.2 mm), meiosis of oogonia occurred to be chromatin nucleolus stage oocyte. The perinucleolus stage oocytes appeared at in 130-days old dap (68.0-86.0 mm), and previtellogenic stage oocytes appeared in 370-days old dap (101.0-116.0 mm). Only female was observed in the artificially produced oblong rockfish in the present study. This result revealed the effect of higher temperature on the sex determination of the oblong rockfish..

• Journal of Aquaculture
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• v.20 no.1
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• pp.47-50
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• 2007

The primordial germ cells of the oblong rockfish, Sebastes oblongus were buried under fibrous mesenchymal tissues between gut and mesonephric duct of pre-larva with 4.0 mm total length (TL) at 1 day after the parturition. In the juvenile of 22.0 mm TL at 71 days after the parturition, the gonad composed of a large number of gonial cell and formed of cavity along the lateral side of the gonad, differentiated to the ovary. At this time, the gonad formed seminiferous tubules by somatic cells, was differentiated to the testis. The smallest oblong rockfish that possessed primary oocytes was about 42.1 mm TL at 141 days. Spermatogonia remained quiescent until most fish were over 42.1 mm TL at 141 days. The oblong rockfish the differentiated directly into male or female without an intermediate female phase at the early indifferentiated stage. Therefore, the oblong rockfish belongs to the differentiated type of gonochoristic teleosts.

• Journal of Aquaculture
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• v.21 no.1
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• pp.7-12
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• 2008

Toxicity of ten commercial disinfectants(hydrogen peroxide, sodium hypochlorite, chlorine dioxide, povidon iodine, formaldehyde, glutaraldehyde, quaternary ammonium compounds(QAC), didecyl dimethyl ammonium chloride(DDAC), ortho-dichlorobenzene, and copper sulfate) was measured by chinook salmon embryo-214 cell line and three fish species: flounder Paralichthys olivaceus, black rockfish Sebastes pachycephalus, and black sea bream Acanthopagrus schlegelii. The $LC_{50}$ levels of 24 hours acute toxicity with the ten disinfectants were tested in three species of fish. Effectiveness of ten chemical disinfectants were varied by each chemical as well as by species. Hydrogen peroxide showed the higest activity at 201, 269, and 139 ppm in the flounder, the black rockfish, and black sea bream, respectively. DDAC showed the lowest activity at 2.1, 1.0, and 1.5 ppm in the flounder, the black rockfish, and black sea bream, respectively. The highest variation was observed in copper sulfate by both the chemicals and the species.

• Journal of Aquaculture
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• v.21 no.1
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• pp.1-6
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• 2008

We determined the effects of dietary supplements for lactic acid bacteria(LAB) such as Lactobacillus brevis(Lb) and Lactobacillus plantarum(Lp) in juvenile rockfish Sebastes schlegeli cultured in flow-through system for 10 weeks. The experimental diets contained $10^4cfu/g,\;10^6cfu/g\;and\;10^8cfu/g$ level each LAB(Lb-4, Lb-6, Lb-8 or Lp-4, Lp-6, Lp-8), respectively. The effects of LAB supplementation was determined by various factor such as weight gain(WG), specific growth rate(SGR), feeding efficiency(FE) and blood assay. For rearing experiment, Lp-8 treatment had significantly high growth rate than control diet treatment. However, all Lb treatment had no significance effect with control diet treatment. In case of the blood assay, hematocrit(Ht) and hemoglobin(Hb) of fish were not affected by LAB supplemental levels. On the other hand, total cholesterol in plasma of Lb-8, Lp-6 and Lp-8 treatments were significantly low than the control diet treatment. We verified the influence of LAB which was originated from species specificity and amount in diet. Consequently, the dietary supplementation as $10^8cfu/g$ level of L. plantarum could be of help for growth enhancement to the juvenile rockfish.

• Development and Reproduction
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• v.10 no.4
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• pp.247-254
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• 2006

It is well publicized that the existence of various endocrine disrupting chemicals threatens normal sexual development of many sedentary marine fishes in the coastal areas. However, a suitable marine fish species for efficient monitoring of this threatening has yet to be identified. One of the difficulties in estimating the effect of endocrine disruption in marine fish is the absence of clear distinction between testicular and ovarian structures at the early stages of sex differentiation. In search of a potential test species, we have investigated the microscopic structures of sexually undifferentiated and differentiated gonads and the susceptibility of gonadal differentiation to exogenous sex steroids during the sex differentiation period in a sedentary marine rockfish, Sebastes schlegeli. Male gonads in this species contained dark pigmentation that made them distinct from female gonads. Treatment either with $estradiol-17\;{\beta}(E_2)$ or $17\;{\alpha}-methyltestosterone$ (MT) significantly altered the sex ratios with the complete sex changes or the occurrence of ovotestis that was easily identified by the mixed structure of dimorphic gonads (coexistence of ovarian cavity/primary oocytes and dark pigmentation/seminiferous tubules). Results in this study suggest that S. schlegeli can be developed as a monitoring/test fish species for endocrine disruption in marine fish in the coastal areas.

• Development and Reproduction
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• v.10 no.3
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• pp.177-184
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• 2006

Retinol-binding protein(RBP) plays an important role in the specific transport of retinol to target cells through the blood stream in higher vertebrates. In order to clarify the effects of 4-nonylphenol(4-NP) on RBP mRNA expression in the rockfish, Sebastes schlegeli which is common in coastal waters of Korea and commercially important species, the cDNA library was constructed from the liver, and a partial fragment of the RBP gene was cloned. The deduced amino acid sequence from the RBP mRNA showed a high homology to the amino acid sequence from Sparus aurata(80%), Oncorhynchus mykiss(72%) or Anguilla anguilla(78%). Effects of 4-NP on RBP and vitellogenin(VTG) mRNA expression level in rockfish were examined by the northern blot analysis. In female and male rockfish injected with 4-NP(10 mg/kg BW, lower dose), there was no changes in the levels of VTG mRNA expression in the liver. The RBP mRNA levels, however, decreased at 48 hours after the injection in male. In the rockfish injected with 4-NP(25 mg/kg BW, higher dose), the level of VTG mRNA expression increased after 24 hours, regardless of sex. The level of RBP mRNA expression decreased at 48 hours after the injection in both sexes. These data indicate that estrogenic mimics such as 4-NP exhibit a contrasting effect on RBP and VTG gene expression in rockfish.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.35 no.6
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• pp.715-722
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• 2002

The monthly collected fish samples by crab pots were analyzed in order to study the species composition and seasonal variation of fish assemblage in the coastal water off Gadeok-do, Korea in 1998, During the study period, 49 species of fishes representing 26 families were collected, The dominant species were Conger myriaster, Sebastes inermis, Hexagrammos otakii, H. agrammus, Stephanolepis cirrhifer and Acanthogobius flavimanus. These 6 dominant species accounted for $67.1\%$ and $69.4\%$ in the number of individuals and biomass, respectively. The secondary importance species were Thamnaconus modestus, Takifugu niphobles, Rudarius ercodes, Dictyosoma burgeri, Sebastes longispinis and Epinephelus septemfasciatus. The highest number of species was collected in November, and the number of individuals and biomass were highest in March. But the lowest numbers of species and individuals were collected in July and the lowest biomass in September, Although the species diversity indices varied little monthly, the lowest value was recorded in August because of small number of species and predominance of 5. cirrhifer and T. modestus.

• Korean Journal of Environmental Biology
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• v.40 no.3
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• pp.247-254
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• 2022

To investigate the tolerance limit and critical thermal maximum (CTM), behavioral responses of wild goldeye rockfish Sebastes thompsoni according to exposure to high water temperature were observed using a continuous behavior tracking system. As a result, behavioral index (BI) of S. thompsoni in each temperature (20.0, 25.0, and 30.0℃) showed a significant difference (p<0.05) when compared with the value measured in a stable condition of 15.0℃. The activity level of S. thompsoni exposed to 25.0℃ decreased sharply after 20 hours. Their rest time at the bottom of experiment chamber increased, and their normal swimming and metabolic activities were disturbed. In addition, at a high water temperature of 30.0℃, S. thompsoni reached the limit of resistance and showed a sub-lethal reaction of swimming behavior, with energy consumption in the body increased and all test organisms died. In conclusion, the eco-physiological response of S. thompsoni to water temperature varied greatly depending on the fluctuation range of the exposed temperature and the exposure time. In addition, the tolerance limit of S. thompsoni to high water temperature was predicted to be 25.0-30.0℃. The maximum critical thermal that had a great influence on the survival of this species was found to be around 30.0℃.