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Climate changes have altered biodiversity and ultimately induced community changes that have threatened the survival of certain aquatic organisms such as fish species. Obtaining biological and genetic information on endangered fish species is critical for ecological population management. Thamnaconus multilineatus , registered as an endangered species by the IUCN in 2019, is a Data Deficient (DD) species with a remarkably small number of habitats worldwide and no known information other than its habitat and external form. In this study, we characterized the external and osteological morphology of a T . multilineatus specimen collected from eastern Jeju Island, South Korea, in 2020. We also investigated the phylogenetic relationships among related fish species through complete mitochondrial DNA (mtDNA) analysis of the T . multilineatus specimen. The external and skeletal characteristics of T . multilineatus were similar to those of previous reports describing other fish of the genus Thamnaconus , making it difficult to classify T . multilineatus as a similar species based only on morphological characteristics. As a result of analyzing the complete mtDNA of T . multilineatus , the length of the mtDNA was determined to be 16,435 bp, and the mitochondrial genome was found to have 37 CDCs, including 13 PCGs, 22 tRNAs, and 2 rRNAs. In the phylogenetic analysis within the suborder Balistoidei, T . multilineatus mtDNA formed a cluster with fish of the genus Thamnaconus . This study is the first to report on the skeletal structure and complete mtDNA of T . multilineatus . Since the current research on T . multilineatus has only been reported on morphology, the results of this study will be utilized as important information for the management and restoration of T . multilineatus as an endangered species and significant fishery resource.

Takifugu genus pufferfish are popular in East Asian countries such as Korea, Japan, and China, but they are avoided as aquaculture species due to slow growth, high cannibalism rates, and susceptibility to diseases. Hybridization is considered one of the most important and efficient breeding methods for aquatic animals, and recent studies have been conducted on hybridization. This study compared optimal water temperature and salinity ranges for hybrid pufferfish by examining three water temperature conditions (15, 20, and 25°C) and five salinity conditions (0, 3, 10, 25, and 33 psu). The hatching rates of hybrid pufferfish embryos were 65.3%, 63.5%, and 67.7% at 0, 3, and 10 psu, respectively, while all embryos died at 25 and 33 psu. Hybrid pufferfish larvae had the highest survival rates at 20°C, and growth rates increased with rising water temperatures. In the salinity experiment, survival rates were 86.0%, 85.0%, 88.0%, and 88.5% at 3 psu, 10 psu, 25 psu, and 33 psu conditions, respectively, with the highest growth observed at 25 psu conditions. Hybrid pufferfish embryos showed good survival in freshwater, but all died in seawater. However, larvae showed good survival and growth in seawater, while all died in freshwater. Therefore, rearing hybrid pufferfish embryos seem suitable at salinities of 10 psu or lower, and increased resistance to salinity was observed in hybrid pufferfish after hatching, indicating that rearing under various salinity conditions ranging from 3 to 33 psu may be feasible.

To investigate the age and growth characteristics of shotted halibut, Eopsetta grigorjewi, in the West Sea of Korea, the samples were collected using gill nets throughout 2019. A total of 861 specimens (693 females and 168 males) were analyzed. The BW-TL relations were BW = 0.0034TL3.3278 (R2 = 0.8716) for females and BW = 0.0031TL3.3359 (R2 = 0.8860) for males. This analysis revealed that males exhibited a larger growth rate than females (p < 0.05). Notably, the anterior and posterior sections of the otolith displayed an elongated oval shape, exceeding the radius of the dorsal and ventral regions. By examining the correlation between radii in four directions and total length, the highest correlation was observed between the total length (TL) and the ventral radius (R). The evaluation of the relationship between the fish total length and the otolith ventral radiusresulted in an equation of TL = 14.657R + 9.1601 (R2 =0.7081) for females and TL = 15.037R + 5.0265 (R2 = 0.6992) for males (p < 0.05). The formation of annuli occurred annually, consistently in January each year, as discerned through monthly changes in marginal index (MI) values. The von Bertalanffy growth equations from the relationship between the otolith annuli radius and the total length were Lt = 83.6 (1 − exp−0.046(t+4.70)) in females (n = 693, p < 0.05) and Lt = 56.8 (1 − exp−0.078(t+2.16)) in males (n = 168, p < 0.05).

In this study, the growth and age characteristics of Okamejei kenojei in the West Sea of South Korea were examined, and specimens were collected by bottom trawls from January to December 2019. The relationship between disc width (L) and body weight (W) was W = 6.1 × 10−3 L3.40. Age was determined by measuring annuli on the vertebral centrum surface, which forms around June every year. The spawning period was extrapolated from monthly changes of the gonadosomatic index in June–July. The relationship between the vertebral centrum radius and disc width, which was analyzed separately for females and males, was determined as L = 16.159R0.6145 and L = 15.543R0.6851, respectively. Finally, O. kenojei growth, that is, the disc width (L) at a certain age (t), was expressed using the von Bertalanffy growth equation as Lt = 58.70(1 − e−0.21(t+0.12)) for females and Lt = 53.94(1 − e−0.26(t+0.05)) for males. This study provides basic data on the age characteristics of O. kenojei for future research and more efficient fish stock management.

Several sampling gears are used to collect fish in the lentic ecosystem. The collected fish differ in their characteristics and community structure depending on the sampling gear. The objectives of this study were to 1) compare the community structure of fish assemblages sampled using four sampling gears (kick net, cast net, gill net, and fyke net) in the Singal (SG), Yedang (YD), and Juam (JA) reservoirs, and 2) to understand the characteristics of fishes collected by each sampling gear. A total of 1887 individuals of 14 species, 9113 individuals of 15 species, and 9294 individuals of 27 species were collected, respectively, from the SG, YD, and JA reservoirs. Among the four sampling gears tested, the fyke net collected the largest numbers of species and individuals, while the gill net collections had the highest diversity index. The results obtained with the self-organizing map (SOM) provided a more detailed characterization of the sampled fish than the metrics that are typically used to evaluate sampling gears. In particular, SOM analysis showed a similar pattern of the standard length of fish and sampling gear. Since each sampling gear has unique characteristics, the selection of an appropriate sampling gear should be based on the study objectives and features of the sampling sites.

To understand the environmental factors affecting the spatiotemporal distribution of copepods, sampling was conducted seasonally in a small mesotidal inlet and estuary located in Doam Bay of southwestern Korea. The study area was divided seasonally into two or three station groups (estuarine, mixed, and coastal) by a cluster analysis and non-metric multidimensional scaling based on copepod abundance. Acartia forticrusa, A. hudsonica, A. ohtsukai, Paracalanus parvus s. l., Pseudodiaptomus marinus, Tortanus derjugini, T. dextrilobatus, T. forcipatus, Oithona spp., and harpacticoids were important species for grouping the stations. The spatiotemporal distribution of the first two species was restricted to the estuarine area in summer and significantly correlated with temperature, salinity, and chlorophyll-a concentration. The distribution of other brackish species, such as T. derjugini and T. dextrilobatus, significantly correlated with temperature, salinity, and chlorophyll-a concentration. In contrast, A. hudsonica significantly correlated with dinoflagellate density and turbidity in winter, in addition to the abovementioned environmental factors. Acartia hudsonica also maintained a large population in the estuarine area in fall and winter, and its distribution extended across the entire bay in spring. Other coastal species occurred in all areas and did not significantly correlate with environmental factors. Therefore, brackish species in the study area may have developed seasonally different behaviors to sustain their populations.

This study aimed to investigate the gonadal development process and size at maturity of the ocellate spot skate Okamejei kenojei (Müller and Henle, 1841). In total, 1234 specimens were collected from the center of the Korean West Sea between January 2019 and December 2020. The maturity stage of the gonads of each individual was determined visually based on size, color, and egg size. To estimate the spawning period, each specimen was measured for disc width, body weight, and gonad weight, and the monthly gonadosomatic index (GSI) was derived. The GSI of the specimens peaked in April and May, and the main spawning period occurred during June and July. Egg capsules were first observed in specimens collected in March and were most commonly observed in specimens collected in July (56.8%). The maturity ogives for disc widths of female specimens at 50%, 75%, and 97.5% maturity were 26.6, 27.9, and 30.8 cm, respectively, whereas those of male specimens were 26.2, 27.5, and 30.7 cm. The findings of this study provide basic information on reproductive ecology related to the fertility of the ocellate spot skate.

In this study, we evaluated the effects of dietary green tea ethanol extract (GTE) supplementation on growth performance, body composition, and stress recovery of the juvenile black rockfish, Sebastes schlegeli . The fish (mean body weight, 8.1 ± 2.0 g) were fed fish meal diets that included 0 % (control), 1, 3, and 5 % GTE for 8 weeks. Weight gain, specific growth rate, feed efficiency, and protein efficiency rate were measured and compared among the fish in the different groups. The whole body and liver lipid compositions of fish fed the control diet were higher than those of the fish fed the GTE diets. Lysozyme activity in the plasma samples of fish fed the GTE diet showed an increasing trend in a dose-dependent manner. After administrating anesthesia (2-phenoxyethanol), the stress recovery time differed significantly between the control and the 3 and 5 % GTE diet groups and the mortality of fish fed on the GTE diet was significantly lower than that of the control group. In addition, plasma glucose levels in the fish fed the 3 % GTE diet showed a rapid recovery. Our results showed that the addition of GTE to the fish diet improved lipid utilization, lysozyme activity and stress recovery, and reduced total cholesterol levels in a dose-dependent manner.

Natural products in Chonnam, the Republic of Korea were screened via anti-angiogenesis experiments, and one candidate product of A. radix extract (ARE) was identified. A. radix extract (ARE) exerted dose-dependent inhibitory effects against angiogenesis, adipogenesis, and cell adhesion. ARE exhibits an angiogenesis inhibitory effect superior to that of the EGCG from the green tea leaves. The expression level of angiogenesis and adipogenesis-related signal molecules in the Western blotting was reduced by increasing the amount of added ARE. Moreover, a diet supplemented with ARE was deemed more effective in inducing weight loss in LB mice than a representative synthetic diet drug, orlistat, which incidentally caused the side effects of denuding the mice of their hair. These results indicate that ARE may prove to be a useful anti-adipogenic compound, and the in vitro results may be reflected at a later time under in vivo conditions.

The principal objective of the present study was to determine the positive effects of artificial illumination on the juvenile black rockfish Sebastes inermis by comparing stomach contents and growth between juveniles exposed to light and those maintained in the absence of light. The major prey items of juvenile black rockfish in illuminated cages were: copepods (%IRI = 62.6); amphipods (%IRI = 36.7); and polychaetes (%IRI = 0.3), whereas those in unilluminated cages were: copepods (%IRI = 93.3); amphipods (%IRI = 6.1); and polychaetes (%IRI = 0.4). The specific growth rates of the juveniles reared in illuminated cages (0.67%) were significantly higher than those juveniles maintained in the unilluminated cages (0.27%).