Korean Rockfish Research Articles

Evidence of gill migration in monogenean polyopisthocotylean Microcotyle sebastis larvae infesting Korean rockfish (Sebastes schlegelii)

In contrast to the well-documented motility of monopisthocotyleans within the monogenean group, the mobility of polyopisthocotyleans, such as Microcotyle sebastis, has largely been undocumented with empirical evidence. This study aimed to investigate the locomotion of the polyopisthocotylean parasite of M. sebastis, which infests Korean rockfish (Sebastes schlegelii), thereby providing tangible evidence of early behavior in polyopisthocotyleans. The oncomiracidium of M. sebastis demonstrated movement facilitated by the hamulus and bilateral cilia, aiding in directional changes and propulsion. In the gill filaments of M. sebastis larvae utilized both the hamulus and their entire body for initial movements, effectively navigating between gill filaments. The hamulus played a crucial role in the locomotion of the early larval stages before the development of three clamp pairs, after which it began to degenerate. This study presents concrete evidence of early mobility in polyopisthocotyleans like M. sebastis, offering insights that could inform aquaculture management strategies, particularly in the mitigation of parasite-induced damages.

Effects of Sweet Wormwood (Artemisia annua L.) in Diet on Growth Performance, Feed Utilization, Body Composition, Blood Chemistry, and Lysozyme Activity of Juvenile Korean Rockfish (Sebastes schlegelii)

Effects of Sweet Wormwood (Artemisia annua L.) in Diet on Growth Performance, Feed Utilization, Body Composition, Blood Chemistry, and Lysozyme Activity of Juvenile Korean Rockfish (Sebastes schlegelii)

First Record and Geographic Expansion of the Sebastes schlegelii in the Sea of Marmara

This study reports the first-recorded presence of the Korean rockfish (Sebastes schlegelii) in the Sea of Marmara, signifying a notable geographical expansion beyond its natural range. The sampled male specimen, with a total length of 27.5 cm and a weight of 459.20 g, aligns with known size patterns observed in the Black Sea, suggesting a consistent trend. The unexpected presence of the species in the Sea of Marmara raises intriguing questions about its potential spread in the broader Mediterranean Sea basin. The adaptability of the Sebastes schlegelii to diverse environmental conditions underscores its ecological resilience. The study emphasizes the need for careful monitoring and management due to potential threats posed by invasive species, especially considering the vulnerabilities of the Sea of Marmara to climate change

Prebosphoric occurrence of Korean rockfish, Sebastes schlegelii Hilgendorf, 1880 in southwestern Black Sea with notes on its morphometry and dispersal potential

On 21 December 2023 one specimen of Sebastes schlegelii Hilgendorf, 1880 have been captured by means of a commercial bottom trawler towed at a depth of 30 m off Şile coast. Following its first occurrence in Turkish Black Sea waters off Giresun coast on 6 March 2023, it has recently reported from the Sea of Marmara (Gulf of İzmit) on 7 January 2024, exhibiting a noteworthy dispersal speed which required less than one year to migrate across nearly a 1,000 km. Therefore, the dispersal and potential interactions with indigenous species of this invasive teleostean along theTurkish coast should be monitored carefully. In the present article, authors provide full morphometric and meristic characters of S. schlegelii, as well.

First Morphological and Genetic Record and Confirmation of Korean Rockfish Sebastes schlegelii Hilgendorf, 1880 in the Black Sea Coast of Türkiye

One specimen of Korean rockfish Sebastes schlegelii Hilgendorf, 1880 was caught by using fish net at a depth of 7 m on 14 May 2022 from Akçakoca, Düzce in Black Sea. In this study, the Korean rockfish Sebastes schlegelii from the Black Sea coast of Türkiye is reported for the first time with both morphologic and genetic evidence. S. schlegelii is characterised by 5 spines on the preoperculum and 2 spines on operculum. Genetic analyses using mtDNA COI gene region also confirmed the species as Sebastes schlegelii. This species is thought to have been transported to the Black Sea from other seas of the world, probably via ballast waters or aquarium escape. The most important reason for this is that the species has not been detected in the Mediterranean.

Assessment of Salinomycin's Potential to Treat Microcotyle sebastis in Korean Rockfish (Sebastes schlegelii).

Aquaculture, a crucial sector of the global food industry, faces a myriad of issues due to parasitic invasions. One such parasite, Microcotyle sebastis, which afflicts Korean rockfish in South Korea, has a significant economic impact. The impending danger of resistance to traditional anthelmintics necessitates the exploration of new antiparasitic candidates. Although the efficacy of salinomycin against aquatic parasites such as ciliates and sporozoans is known, its influence on monogeneans has yet to be studied. Therefore, this study investigated the efficacy and safety of salinomycin for the treatment of M. sebastis infections, presenting the first exploration of salinomycin's therapeutic potential against monogeneans. In vitro examinations revealed a minimum effective concentration of salinomycin of 5 mg/kg, which led to necrosis of the haptor upon dislodging from the gill filaments. The one-time oral administration of the drug at concentrations of 5 mg/kg and 10 mg/kg showed a significant dose-dependent reduction in parasite counts, with no apparent behavioral side effects in Korean rockfish. Biochemical analyses monitored the liver, heart, and kidney enzymes, specifically aspartate transaminase (AST), alanine transaminase (ALT), blood urea nitrogen (BUN), and creatine kinase-myocardial band (CK-MB). At both 20 °C and 13 °C, no significant differences were observed in the levels of AST and ALT. However, at 20 °C, alterations in BUN levels were evident on Day 14, a deviation not observed at 13 °C. The CK-MB analysis revealed elevated enzyme levels at both temperatures when compared to the control group, reflecting the similar changes observed in terrestrial animals administered salinomycin. The biochemical data suggest that the oral administration of salinomycin is potentially more favorable at 13 °C than at 20 °C. Although our findings warrant further comprehensive studies, including on the long-term and potential effects on nontarget species and water quality, they also suggest that salinomycin could be considered as an alternative or adjunctive treatment if resistance to the currently used praziquantel against M. sebastis is confirmed.

Effects of water temperature and light/dark cycles on in vitro egg laying and hatching of the monogenean Microcotyle sebastis on Korean rockfish (Sebastes schlegelii)

Aquaculture faces increasing challenges from parasitic infections, notably impacting the marine cage farming of Korean rockfish (Sebastes schlegelii). A primary contributor to these challenges is the monogenean parasite Microcotyle sebastis, which incurs significant economic losses. To formulate effective management strategies, it is essential to understand how environmental variables influence the reproductive behavior and survival of M. sebastis. In this study, we conducted controlled in vitro experiments to assess the fecundity, hatching success, and viability of M. sebastis across a temperature range from 25 °C to 4 °C, as well as under varying light/dark conditions. We found that the parasite's fecundity was optimal at 15 °C and minimal at 4 °C. Survival rates exhibited an inverse correlation with increasing temperatures. The hatching process was most rapid at 25 °C, with no hatching observed at 4 °C. Upon hatching, the maturation and lifespan of oncomiracidia varied depending on temperature: cilia degenerated within 36 h at temperatures ranging from 25 °C to 15 °C, whereas at 10 °C, cilia began to degenerate on the fourth day post-hatching, surviving for up to nine days. Interestingly, conditions of perpetual darkness led to increased egg production and survival rates compared to light exposure. Our findings provide critical insights into the adaptive responses of parasites to environmental changes and suggest that current deworming strategies may not adequately address the rapid hatching and increased egg production of M. sebastis. We emphasize the need for ongoing research to adapt aquaculture management strategies to the evolving challenges posed by parasites and recommend that future research focus on field studies examining the impact of environmental variables and multiple parasite species.

Correlation of endemicity between monogenean trematode, Microcotyle sebastis, and parasitic copepods in Korean rockfish, Sebastes schlegelii, from a fish farm in Tongyeong-si, Gyeongsangnam-do, Korea.

Infestations of parasites, particularly those caused by copepods and monogeneans, are a major hindrance to aquaculture and have a big negative economic impact. Sebastes schlegelii, a farmed Korean rockfish, is particularly prone to copepods and monogeneans. This study comprehended how parasitic copepods and rockfish from a farm in Tongyeong-si, Gyeongsangnam-do, Korea, are related to the monogenean trematode Microcotyle sebastis. Our research revealed that monogeneans predominated, with a rate of 98.4% and an average infection intensity of 7 per infected fish. With an average infection intensity of 4 per sick fish, the infection rate for parasitic copepods was equally considerable, coming in at 91.7%. The high co-infection rate of both parasite families, at 90.8%, is noteworthy. Furthermore, Lepeophtheirus elegans and Peniculus truncatus, 2 parasitic copepod species, were discovered to have M. sebastis eggs attached to their bodies. This demonstrates a connection between parasitic copepod infestations in farmed Korean rockfish and the monogenean trematode M. sebastis. These discoveries highlight the necessity for creating more potent parasite control methods for the aquaculture sector and shed light on the intricate relationships between various parasite species.

Exploring the Efficacy and Safety of Levamisole Hydrochloride against Microcotyle sebastis in Korean Rockfish (Sebastes schlegelii): An In Vitro and In Vivo Approach.

Parasitic infections pose significant challenges in aquaculture, and the increasing resistance to conventional anthelmintics necessitates the exploration of alternative treatments. Levamisole hydrochloride (HCl) has demonstrated efficacy against monogenean infections in various fish species; however, research focused on Microcotyle sebastis infections in Korean rockfish (Sebastes schlegelii) remains limited. Therefore, this study aimed to evaluate the efficacy of levamisole HCl against M. sebastis infections in Korean rockfish with the goal of optimizing anthelmintic usage in aquaculture. In this study, we first assessed the susceptibility of M. sebastis to levamisole HCl in vitro. Subsequently, in vivo evaluations were conducted to assess the drug's efficacy, safety, and to identify optimal administration methods. In vitro experiments revealed concentration-dependent sensitivity of M. sebastis to levamisole HCl, with a minimum effective concentration (MEC) of 100 mg/L. In vivo experiments employed oral administration, intraperitoneal injection, and immersion treatments based on the MEC. Oral administration proved to be a safe method, yielding efficacy rates of 27.3% and 41.6% for 100 mg/kg and 200 mg/kg doses, respectively, in contrast to the immersion and injection methods, which induced symptoms of abnormal swimming, vomiting, and death. Biochemical analyses conducted to assess the safety of levamisole HCl revealed a transient, statistically significant elevation in the levels of glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) on day three post-administration at 20 °C. Following this, no substantial differences were observed. However, at 13 °C, the enzyme levels remained relatively consistent, emphasizing the role of water temperature conditions in influencing the action of levamisole HCl. Our research findings substantiate the efficacy of levamisole HCl against M. sebastis in Korean rockfish, underscoring its potential for safe oral administration. These results provide valuable insights for developing parasite control strategies involving levamisole HCl in Korean rockfish populations while minimizing adverse impacts on fish health and the environment. However, this study bears limitations due to its controlled setting and narrow focus. Future research should expand on these findings by testing levamisole HCl in diverse environments, exploring different administration protocols, and examining wider temperature ranges.

Analyses of regulatory network and discovery of potential biomarkers for Korean rockfish (Sebastes schlegelii) in responses to starvation stress through transcriptome and metabolome

Whether in aquaculture or in nature, starvation stress limits the growth of fish. The purpose of the study was to clarify the detailed molecular mechanisms underlying starvation stress in Korean rockfish (Sebastes schlegelii) through liver transcriptome and metabolome analysis. Transcriptome results showed that liver genes associated with cell cycle and fatty acid synthesis were down-regulated, whereas those related to fatty acid decomposition were up-regulated in the experimental group (EG; starved for 72 days) compared to the control group (CG; feeding). Metabolomic results showed that there were significant differences in the levels of metabolites related to nucleotide metabolism and energy metabolism, such as purine metabolism, histidine metabolism and oxidative phosphorylation. Five fatty acids (C22:6n-3; C22:5n-3; C20:5n-3; C20:4n-3; C18:3n-6) were selected as possible biomarkers of starvation stress from the differential metabolites of metabolome. Subsequently, correlation between these differential genes of lipid metabolism and cell cycle and differential metabolites were analyzed, and observed that these five fatty acids were significantly correlated with the differential genes. These results provide new clues for understanding the role of fatty acid metabolism and cell cycle in fish under starvation stress. It also provides a reference for promoting the biomarker identification of starvation stress and stress tolerance breeding research.

Effect of surgical staples and stitches on the critical swimming speed of Sebastes schlegelii after implantation of ultrasonic pingers

Implantation of ultrasonic pingers in fish is invasive in nature, as it bisects epidermis and skin tissues, with negative health impacts on the individual. Taking Korean rockfish Sebastes schlegelii as a model species, we compared the difference between using surgical sutures and disposable-staple sutures so as to minimize the impact caused by implantation. The results showed that (1) the critical swimming speed of S. schlegelii changed significantly 2 h after surgery but did not change significantly 1 d after the operation; (2) both suture methods can effectively close the wound; and (3) it takes less time to suture the wound with disposable skin staples than with a surgical needle. The abdominal incisions of the experimental fish were clean, the fish showed no inflammation or necrosis after suture by the 2 methods, and they remained healthy for 7 d after operation. We conclude that disposable skin staples are well suited for minimally invasive surgical suturing.

딥러닝 기법을 활용한 양식산 조피볼락 산지가격 예측 연구 －LSTM(Long-short Term Memory)과 GRU(Gated Recurrent Units) 모델을 중심으로－

This study is aimed to forecast the producer price of aquaculture seafood using LSTM(Long-short Term Memory) and GRU(Gated Recurrent Units) models, a type of deep learning model. Since the producer price is directly related to aquacultural farm’s profitability, accurate forecasting of the producer price is essential to establish an effective production and management plan for aquaculture and stabilize supply and demand of farmed seafood. Korean Rockfish(Sebastes schlegelii) is a commercially important fish species that ranks second in domestic farmed fish production and is the main breed of fish farms in Tongyeong region. As the volatility of the producer price of Korean Rockfish has recently intensified, the importance of forecasting the producer price is increasing. In the analysis, total 19 variables were used, including producer prices in other regions, production-related variables, consumption-related variables, alternative farmed fish variables, water temperature, and COVID-19 dummy variables. Total 189 monthly data from October 2006 to June 2022 were used. In this study, the producer price of farmed Korean Rockfish was forecasted by LSTM and GRU models, a type of RNN(Recurrent Neural Network) model specialized for time series forecasting and the accuracy of models was compared with MAPE(Mean Absolute Percent Error). Results showed that MAPEs of LSTM and GRU were 4.66% and 6.27%, respectively. In addition, when comparing the accuracy by the number of independent variables, it was found that the accuracy of the multivariate LSTM model was better than that of the univariate LSTM model.

액화산소와 산소용해기 설치에 따른 해상가두리 양식장의 고수온 피해저감 효과

This study investigated the effect of damage reduction devices installed to reduce the mass mortality of farmed fish at high water temperatures period in marine net cage. The effect of rearing densities on fish mortalities in summer was also investigated. It was found that, dissolved oxygen and survival rate of Korean rockfish, Sebastes schlegeli in the experimental groups, i.e. the net cages equipped with liquefied oxygen and oxygen dissolver and with a lower rearing density were found to be higher than in the controls, i.e. net cages without the above devices and a higher density. According to the blood analysis results of the experimental fish, hemoglobin, hematocrit, glucose, glutamic oxalate transaminase (GOT) and glutamic pyruvate transaminase (GPT) in the fish of the control cage without damage reduction devices increased while the same blood parameters in the fish of the experimental group showed no significant difference from the initial values. Dissolved oxygen concentrations were found to be higher in the group with the combined use of both liquefied oxygen and oxygen dissolver than in the group with the single use of either device. It was concluded that the damage reduction devices and lower rearing densities were effective to raise dissolved oxygen concentrations in the high water temperature period.

풍력발전 건설 시 발생하는 수중소음이 조피볼락(Sebastes schlegelii)의 생리 및 면역요인에 미치는 영향

Wind power generation is a promising power generation facility field that is developing due to interest in environmental protection and technological development. However, disturbance to humans and animals has been reported due to noise generated during construction and operation. Therefore, we attempted to evaluate the immune and physiological effects of stress caused by a sound pressure range of 125–155 dB/μPa in Korean rockfish (Sebastes schlegelii), a major aquaculture fish species in South Korea, by reproducing the noise generated during the construction of a wind power plant. Significant effects were confirmed for molecular biological and serological indicators, and serious mortality occurred due to artificial infection. These results indicate a more fatal effect on animals in aquaculture farms, which cannot move or avoid undesirable habitats, unlike animals in natural conditions. Thus, it is important to develop measures for environmental noise management.

Development of a PCR-RFLP method for differential identification of Microcotyle sebastis and Microcotyle caudata isolated from cultured rockfish in Korea.

Microcotylid monogeneans can cause considerable health problems in cultured fish, and several Microcotyle species are reported from scorpaenid fish, an economically important aquaculture target species in Korea. We developed a PCR-RFLP assay targeting the mitochondrial cox1 gene, for discriminating Microcotyle sebastis and M.caudata from cultured Korean rockfish Sebastes schlegelii and dark-banded rockfish S.inermis. AseI enzyme treatment of the PCR products showed that M.sebastis sequence was cleaved while M.caudata was not. A total of 95.2% (118/124) of monogeneans from S.schlegelii were identified as M.sebastis, and 96.2% (126/131) of monogeneans from S.inermis were identified as M.caudata by PCR-RFLP. However, the remaining parasites from each host showed the opposite digestion pattern. Additional analyses of these specimens by targeting the ITS region by PCR-RFLP showed the same results, suggesting that cross-species infection by the parasites may have occurred. In Korea, S.inermis net cages are commonly located nearby S.schlegelii net cages, and this encaged proximity might have provided the opportunity for cross-infection to occur. Further examination of wild host populations and experimental cross-infection will be necessary to explain this phenomenon. The PCR-RFLP method in this study will help investigate the epidemiology and infection dynamics of Microcotyle species in S.inermis.

Evaluating Impacts of Trophic Interactions on the Effectiveness of Single-Species Fisheries Management

Single-species fisheries management (SSFM) is applied to many fisheries ecosystems around the world. The associated ecological impacts are usually not well understood due to the lack of considering trophic interactions among species in the ecosystem. This impedes the implementation of SSFM in an ecosystem context and reduces our ability to understand the possible ecological impacts of fishing activities. This study focuses on two economically important species in the Jiaozhou Bay, China: the short-lived, fast-growing, and relatively abundant Japanese mantis shrimp (Oratosquilla oratoria) and the long-lived, slow-growing, and less abundant Korean rockfish (Sebastes schlegelii). We evaluated how varying trophic interactions influenced O. oratoria and S. schlegelii (i.e., target-species) who were managed under constant fishing pressure. The increase of fishing pressure to other species (i.e., non-target species) was beneficial to O. oratoria and S. schlegelii. O. oratoria was more sensitive to the decrease of fishing pressure to other species. The predation mortality of age-0 O. oratoria increased with the increased fishing pressure to other species. The predation mortality of age-1 O. oratoria and age-0 S. schlegelii had negative relationships with the fishing pressure to other species. Age-1 S. schlegelii seemed not to be sensitive to the changes in trophic interactions. The predation mortality of O. oratoria and S. schlegelii had bigger changes than the starvation mortality after fishing changed. It suggested the prey-predator relationship had a bigger impact than the food competition. The increase of high-trophic-level fish Johnius belangerii fishery positively impacted O. oratoria, but negatively impacted S. schlegelii. S. schlegelii was more sensitive to the changes of the low-trophic-level fish Pholis fangi fishery. Given the complex dynamics of ecosystems, this study highlights the importance of species-specific responses of fishes to shifting trophic interactions in fisheries management.

Comparison of Intestine Microbiota Between Wild and Farmed Korean Rockfish, Sebastes schlegelii

Comparison of Intestine Microbiota Between Wild and Farmed Korean Rockfish, Sebastes schlegelii

Trophic interactions of reef-associated predatory fishes (Hexagrammos otakii and Sebastes schlegelii) in natural and artificial reefs along the coast of North Yellow Sea, China

Large reef-associated predatory fishes play important roles in aquatic ecosystem along coast because of their ecological functions and economic values to recreational and commercial fisheries. This study was carried out to assess the function of artificial reefs as alternative habitats for two common reef-associated predatory fishes in the north of Yellow Sea, China, Fat Greenling Hexagrammos otakii and Korean rockfish Sebastes schlegelii. According to the catch per unit effort (CPUE), the biomass of predatory fishes at the artificial reef was comparable (H. otakii) to or higher (S. schlegelii) than the natural reef, highlighting the environmental fitness of the artificial reef. Gut content analysis (GCA) showed that H. otakii preyed primarily on Decapod and Amphipoda, while S. schlegelii exhibited higher dependence on fish (Blinniidae and Gobiidae) and Decapod. Collectively, prey richness and diversity were greater at the natural reef relative to the artificial reef, and prey availability may be different between the two reef types. Stable isotopic analysis (SIA) in conjunction with the Bayesian mixing model (MixSIAR) revealed spatial and interspecific difference on the diet composition of H. otakii and S. schlegelii as well. Based on GCA and MixSIAR result, the habitat-specific effect on the prey availability was confirmed. Additionally, comparisons on trophic niche breadth and niche overlap indicated higher trophic diversity but relatively lower food resources partitioning degree for both species at the natural reef than at the artificial reef. Our results suggest that artificial reefs may harbor a different prey assemblage comparing to natural reef but can support large populations of predatory reef-associated fishes and accommodate their coexistence.

Occurrence and Molecular Identification of Microcotyle sebastis Isolated from Fish Farms of the Korean Rockfish, Sebastes schlegelii.

Microcotyle sebastis is a gill monogenean ectoparasite that causes serious problems in the mariculture of the Korean rockfish, Sebastes schlegelii. In this study, we isolated the parasite from fish farms along the coasts of Tongyeong, South Korea in 2016, and characterized its infection, morphology and molecular phylogeny. The prevalence of M. sebastis infection during the study period ranged from 46.7% to 96.7%, and the mean intensity was 2.3 to 31.4 ind./fish, indicating that the fish was constantly exposed to parasitic infections throughout the year. Morphological observations under light and scanning electron microscopes of the M. sebastis isolates in this study showed the typical characteristics of the anterior prohaptor and posterior opisthaptor of monogenean parasites. In phylogenetic trees reconstructed using the nuclear 28S ribosomal RNA gene and the mitochondrial cytochrome c oxidase I gene (cox1), they consistently clustered together with their congeneric species, and showed the closest phylogenetic relationships to M. caudata and M. kasago in the cox1 tree.

Replacement of Dietary Vitamin C with Citrus and Fermented Citrus By-products in Korean Rockfish Sebastes schlegelii

Replacement of Dietary Vitamin C with Citrus and Fermented Citrus By-products in Korean Rockfish Sebastes schlegelii