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BackgroundThe brown croaker, Miichthys miiuy, is an economically important fish species in Korean waters. Research on the spawning ecology of M. miiuy in Korea has primarily focused on specimens from the southwestern waters, assessing parameters, such as spawning season and mature body length through histological examination. However, a comprehensive histological analysis across various body sizes during the spawning season is imperative to accurately ascertain these factors, as well as for efficient resource management amidst potential environmental variations. Therefore, this study was undertaken to investigate the spatiotemporal distribution and reproductive biology of M. miiuy in the southwestern waters of Korea.MethodsMonthly changes in gonadal maturity stages, gonadosomatic index (GSI), egg diameter, and fecundity were analyzed. Additionally, total length at sexual maturity at 50%, 75%, and 97.5%, as well as the sex ratio, were determined.ResultsM. miiuy, captured using offshore gillnets and stow nets, exhibited a seasonal migration pattern: a winter presence near Jeju Island, followed by a northward movement in spring, a summer shift to the shallow waters of Shinan, and an autumnal migration to the waters around Jeju Island for overwintering. The overall female-to-male sex ratio was 1:0.8. GSI values peaked in September and August for both sexes; however, microscopic analysis of gonadal tissue revealed a spawning period from July to September 2023, with the primary spawning season for the entire population occurring in August and September. The fork length at 50% maturity was 57.4 cm for females and 54.6 cm for males.ConclusionOverall, these results suggest an earlier shift in the spawning period of brown croakers in the southwestern waters of Korea compared to past observations. This shift is potentially attributable to higher water temperatures, increased resource levels, and alterations in the species composition of major prey items in the spawning grounds. Further research is imperative for a comprehensive understanding of the factors influencing the reproductive ecology of this important fish species.

The present case report aims to outline the post-mortem findings of an East Asian finless porpoise with upper aerodigestive tract obstruction using different post-mortem computed tomography (PMCT) visualization techniques and discusses the potential cause of death of this individual. A dead-stranded adult male East Asian finless porpoise was recovered from the Northern coast of Jeju Island, Republic of Korea. The carcass was frozen in Jeju National University within 2 h upon first reported. The PMCT examinations were performed at 120 kVp, 200 mAs with a section thickness of 1 mm. The scan field of view (sFOV) was set to 400 mm. Four image rendering techniques, including multi-planar reconstruction, three-dimensional volume rendering, perspective volume rendering, and minimum intensity projection technique, were used to aid the diagnosis of upper aerodigestive tract obstruction in the stranded finless porpoise. Conventional necropsy was performed to provide a complete necropsy report. Using PMCT, a Sebastidae of 24 cm measured length was found to be lodged in the left pharyngeal food channel and esophagus of the finless porpoise. Hard rays of the pectoral fin of the lodged fish have impaled the esophageal mucosa. Fishing gear was found to embed at the dorsal side of the lodged fish. The trachea was compressed ventrally and the arytenoepiglottic tube opening has been narrowed, which may precipitate to the finless porpoise difficult breathing. Pulmonary hyperinflation, pulmonary edema, pneumothorax, pneumopericardium, and pneumorrhachis were observed. This case report represents the first documentation of potential radiological indicators of upper aerodigestive tract obstruction in the East Asian finless porpoise using PMCT. Spatial location of the lodged item could be rendered in situ as the time of death. It has demonstrated that PMCT could provide objective measurements to adjunct the necropsy findings in diagnosis of fatal aerodigestive tract obstruction in stranded cetaceans.

Understanding feeding ecology is essential for ecosystem-based management. As dietary data can show differences depending on the spatiotemporal and ontogenetic aspects of the sample, the results should be derived based on various size classes and samples over a wide spatiotemporal range. Morphological analysis of the stomach contents of Dissostichus mawsoni , a piscivore, collected at depths of 603–2,113 m in subarea 88.3 during the Antarctic summer fishing seasons from 2016 to 2020 was used to assess the dietary composition according to the research block, fishing season, depth, and size. Here, we used 1,639 D. mawsoni specimens with a total length range of 44.5–189.0 cm. The dietary composition of D. mawsoni did not show significant differences by fishing season but differed with research block, depth, and size. Macrouridae dominated research blocks 88.3_1 and 88.3_3; Nototheniidae dominated research blocks 88.3_2 and 88.3_6; and Channichthyidae dominated research blocks 88.3_4 and 88.3_5. The proportion of Nototheniidae decreased as depth increased, whereas the consumption of Channichthyidae increased gradually with depth in research blocks 88.3_3 and 88.3_4. The proportion of Channichthyidae decreased as body size increased, whereas the consumption of Macrouridae increased gradually with body size in both blocks 88.3_3 and 88.3_4. During the study period, the dietary composition of D. mawsoni in both blocks 88.3_3 and 88.3_4 did not show significant temporal differences, suggesting that these data could be used as a baseline for identifying future environmental changes in the region. This study provides information on the relationships between various species and benthic fish fauna, which are essential for ecosystem-based management.

Stomach contents of the Antarctic toothfish, Dissostichus mawsoni , collected from subareas 58.4 and 88.3, were analyzed using next generation sequencing (NGS) technology. After processing the raw reads generated by the MiSeq platform, a total of 131,233 contigs (130 operational taxonomic units [OTUs]) were obtained from 163 individuals in subarea 58.4, and 75,961 contigs (105 OTUs) from 164 fish in subarea 88.3. At 98% sequence identity, species names were assigned to most OTUs in this study, indicating the quality of the DNA barcode database for the Antarctic Ocean was sufficient for molecular analysis, especially for fish species. A total of 19 species was identified from the stomach of D. mawsoni in this study, which included 14 fish species and five mollusks. More than 90% of contigs belonged to fish species, supporting the postulate that the major prey of D. mawsoni are fish. Two fish species, Macrourus whitsoni and Chionobathyscus dewitti , were the most important prey items (a finding similar to that of previous studies). We also obtained genotypes of prey items by NGS analysis, identifying an additional 17 representative haplotypes in this study. Comparison with three previous morphological studies and the NGS-based molecular identification in this study extended our knowledge regarding the prey of D. mawsoni , which previously was not possible. These results suggested that NGS-based diet studies are possible, if several current technical limitations, including the quality of the barcode database or the development of precise molecular quantification techniques to link them with morphological values, are overcome. To achieve this, additional studies should be conducted on various marine organisms.

Background Human fishing activities have significantly affect environmental concern for marine ecosystems, conservation of marine mammals, and human health. Coastal cetaceans are highly vulnerable to ingestion of fishing gear, bycatching, or entanglement, all of which can be fatal for these animals. In particular, certain coastal dolphins and porpoises are heavily impacted by fishing gear such as angling gear or stownet, as their food often overlap with the target fish species of human fisheries. Case presentation This study presents a case of an Indo-Pacific finless porpoise ( Neophocaena phocaenoides ) beached on the coast of Jeju Island, Republic of Korea, with ingestion of fishing gear and severe Anisakis infection. Although this species inhabits waters ranging from the Persian Gulf to Taiwan, several stranded carcasses have been reported on Jeju Island in recent years. Post-mortem computed tomography revealed a bundle of four fishing hooks in the forestomach, along with nylon lines and steel lines with connectors, which were assumed to be angling gear for Jeju hairtail ( Trichiurus lepturus ). Further necroscopic investigation revealed that the forestomach contained a large number of Anisakis spp. (Nematoda: Anisakidae). Histological examination revealed a thickened forestomach wall with pinpoint and volcanic ulcerations, a thickened layer of stratified squamous epithelium, and infiltrated stroma in the squamous epithelium. conclusions This study emphasizes the urgent need to address the impact of fishing activities on marine mammals, marine litter pollution, and the bycatch problem in Korean seawater. In addition, the occurrence of N. phocaenoides in seawater around Jeju Island should be raised in future geographical ecology or veterinary pathology studies and when its distribution is updated.

Variability in the diet breadth of two sympatric mudskippers Periophthalmus modestus and P. magnuspinnatus in the tidal flats of Suncheon Bay, Korea, was compared. The analysis of 494 P. modestus and 455 P. magnuspinnatus specimens revealed that both were carnivores, consuming mainly gammarid amphipods, polychaetes, insects, and crabs. However, adult P. modestus consumed greater proportions of polychaetes whereas P. magnuspinnatus ate more crabs. The diets of both species showed ontogenetic changes in diet; smaller individuals of both species consumed harpacticoid copepods and gammarid amphipods, whereas larger fishes of both species fed mainly on different preys. The stomach content index (SCI) of both species underwent significant size-related and diel changes; the values of both species were higher in the larger size classes and during the late afternoon. Levin's index of diet breadths of both species were lower during the day than at night, indicating high prey selection during the daytime. Non-metric multi-dimensional scaling ordination emphasized that the dietary compositions of the smaller individuals of both species showed some obvious similarities, with dietary similarity gradually reducing with increasing fish size. This indicates that the two species consume gradually different types of prey as they grow, that is, resource partitioning may be occurring between larger P. modestus and P. magnuspinnatus.

The feeding habits of Helicolenus hilgendorfii were studied using 93 specimens (35–135 mm in standard length) collected from the southeastern coast of Korea during the summer season (June–August) from 2005 to 2007. Helicolenus hilgendorfii is a carnivore that mainly consumes shrimps and fishes. Its diet also includes small quantities of mysids, amphipods, euphausiids, copepods, and isopods. Our graphical method for feeding habits revealed that H. hilgendorfii is an opportunistic and specialized predator on shrimps, especially Crangon hakodatei, although H. hilgendorfii showed an ontogenetic dietary shift, the proportion of shrimp decreasing and the consumption of fishes gradually increasing with the increase of fish size.

Feeding ecology was compared between sympatric greenling species, Hexagrammos otakii and H. agrammus in the eelgrass beds in Jindong Bay, Korea, from January to December. These two species had similar diets composed of crustaceans, polychaetes, gastropods and fishes; both species consumed primarily crustaceans throughout study periods. H. otakii, however, fed a greater proportion of polychaetes and fishes than H. agrammus. H. agrammus had a greater proportion of gastropods in their diets. The diet of both species underwent size-related changes; smaller individuals of H. otakii and H. agrammus consumed amphipods (gammarid amphipods and caprellid amphipods), while larger individuals of H. otakii ate polychaetes and fishes and those of H. agrammus fed mainly on gastropods and crabs. The diet of H. otakii underwent seasonal changes; H. otakii consumed mainly polychaetes and fishes during January and February 2002 but amphipods during March and May 2002. H. agrammus, however, ate mainly gastropods and crabs all seasons. H. otakii underwent also a significant diel changes that could be related to difference of prey availability. Thus the nocturnal emergence of gammarid amphipods, polychaetes and fishes explained their greater consumption by H. otakii. Dietary breadth of both species was lower in the smallest individuals (<5 cm SL) and in March and April 2002. This was due to the disproportionate dry mass attributable to the consumption of amphipods by both H. otakii and H. agrammus. Dietary overlap of both species was relatively moderate to high, in particular in <9.9 cm SL (0.62 - 0.71) from May to July 2002 (0.63 - 0.71). This is coincident with higher abundances of crabs, caridean shrimps and polychaetes in the study area, and it was assumed that these prey species were not limited resources. Higher dietary overlap was correlated with an abundance of a shared resource and did not indicate the interspecific competition between H. otakii and H. agrammus.[PUBLICATION ABSTRACT]

Kim, H.J.; Baeck, G.W.; Lee, J.H.; Lee, S.-J.; Kang, S., and Jeong, J.M., 2023. Distribution of food resources for two species of the skate family (Beringraja pulchra and Okamejei kenojei) in the South Sea of Korea. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 588-592. Charlotte (North Carolina), ISSN 0749-0208. Beringraja pulchra and Okamejei kenojei belong to the Rajidae family of the order Rajiformes. They have similar morphological features, and both species are bottom fishes. B. pulchra and O. kenojei used in this study were caught by the National Institute of Fisheries Research in Tamgu 21, 22, and 23 with bottom trawl in the South Sea. Major food organisms were identified by calculating the relative importance index ratio for the two species, and food quality was compared by analyzing changes in food organisms and nutritional levels according to season and growth. A total of 192 B. pulchra were used in this study, of which 160 were analyzed except for empty stomachs, and a total of 202 O. kenojei were analyzed for 169 other than empty stomachs. The appearance width of the B. pulchra was 9.8–53.1 cm, and the apparent width of the O. kenojei was 8.3–41.2 cm. As a result of analyzing the relative importance index of the two species, macrura were the highest in both species, with 63.8 % of B. pulchra and 97.4 % of O. kenojei, which indicates that the main prey of the two species was macrura. The two species mainly consume macrura, but it is believed that they avoid competition and divide food resources by consuming preferred food organisms other than macrura.

Baeck, G.W.; Seong, G.C.; Kang, D.Y.; Jin, S.; Soh, H.Y., and Kim, D.-G., 2023. Feeding habits of jack mackerel, Trachurus japonicus, in the coastal waters of South Sea, Korea. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 573-577. Charlotte (North Carolina), ISSN 0749-0208. To investigate the feeding habits of the jack mackerel, Trachurus japonicus, in the coastal waters of South Sea, Korea, fish samples were collected by a set net and purse seine fishery in March 2020 to February 2022. The Fork Length (FL) of these specimens was from 5.1 to 50.7 cm. T. japonicus were a carnivore that fed mainly on euphausiids and fishes. In addition, T. japonicus fed on small quantities of copepods, shrimps, cephalopods etc. T. japonicus underwent an ontogenetic dietary shift. The proportion of fishes and copepods decreased as body size increased, whereas the consumption of euphausiids increased gradually. Examination of the feeding habits according to ontogenetic feeding patterns in the diets of T. japonicus revealed that the mean number of prey (mN/ST) and mean weight of prey (mW/ST) continuously increased. Euphausiids most common prey during spring, autumn and winter, whereas fishes were mainly consumed during summer. Permutational Multivariate Analysis of Variance (PERMANOVA) revealed significant dietary differences by size class, and the interaction between the season and size class. T. japonicus were specialized feeders with euphausiids and fishes as their dominant prey.