Fish samples were collected by a set net from April to December 2020 at the coastal waters off Tongyeong, Korea to determine fish species composition and seasonal variation. A total of 330,675 fish (1,032,578 g) representing 56 species belonging to 39 families were collected during the sampling period. The dominant species were Engraulis japonicus, Trachurus japonicus and Trichiurus japonicus, which accounted for 98.1% of the total number of individuals and 87.5% of the total biomass collected. E. japonicus and Chelidonichthys spinosus appeared every month off the coast of the Tongyeong. Cluster analysis based on the number of individuals of fish were classified into two groups at the dissimilarity level of 57%, and the results of ANOSIM analysis revealed significant differences in community structure among the two groups

This study analyzed the reproductive biology, fishing characteristics and changes in fishing business of Liparis tanakae, snailfish collected from September to March. It was the period when they were mainly caught from 2018 to 2020. The average length was generally small in September and October and was large in January and February. The average body weight was generally around 1,500 g and the average body weight in autumn was lower and in winter was higher. The sex ratio of male and female was 0.40:0.60 (χ 2 test, p < 0.05). The spawning period was estimated from October to February and the main spawning period was from December to February through the GSI. The egg diameter of matured staged female L. tanakae was 0.11-1.48 mm, which was the main spawning period and the relationship between body weight and fecundity was F = 1849TL0.1093 (r2 = 0.2401). The monthly catch of L. tanakae was high from November to February, the time of migrating to the coastal area. Coastal gillnet fishery showed the highest percentage of all fisheries catching Liparis spp. Liparis spp. were caught at a high rate in winter in Chungnam, Jeonbuk, Jeonnam and Gyeongnam region, and revenue and cost was increased since 2017. Assuming a situation where there is no catch of Liparis spp., the fishing profit that can be obtained was the highest in Gyeongnam region and the dependence on fishing of Liparis spp. by coastal gillnet fishery was high.

The feeding habits of the bighead croaker Collichthys niveatus were studied using 745 specimens collected by bottom trawl net in the West Sea, Korea, in April and October of 2016, 2017 and 2018. The size of C. niveatus ranged from 4.8 to 16.0 cm in total length. The stomach contents analysis indicated that C. niveatus consumed mainly euphausiids and copepods. C. niveatus consumed mainly euphausiids and copepods in all size classes. The dietary compositions of C. niveatus was not significantly different among size classes (One-way ANOVA, P > 0.05). As body size of C. niveatus increased, the mean weight of prey per stomach (mW/ST) tended to increase.

The diet composition of Arctoscopus japonicus was studied using 448 specimens collected in the coastal waters of East Sea, Korea. The size of the specimens ranged from 6.2-25.3 cm in total length (TL). A. japonicus were fed mainly on amphipods that constituted 76.1% in IRI. Euphausiids were the second largest prey component. The diets also include small quantities of crabs, copepods, mysids, cephalopods, monogeneans, and fishes. A. japonicus showed ontogenetic changes in feeding habits. Smaller individuals (6-10 cm, TL) fed mainly on amphipods. The proportion of amphipods decreased as body size increased, whereas the consumption of euphausiids gradually increased (10-14 cm, TL). As the body size more increased, the proportion of amphipods increased whereas euphausiids decreased (14-26 cm, TL).

It was turned out by shrimp beam trawl monthly survey from March, 2015 to February, 2016 that different species composition and abundance of the fish assemblages in Sacheon Bay and coastal waters off Namhae, Korea were compared. As a result of monthly measured sea temperature and salinity of Sacheon Bay and coastal waters off Namhae, sea temperature of both areas was changed seasonally; however, differences in sea temperature occurred during certain periods depending on the region. Salinity was generally low in Sacheon Bay affected by fresh water, and both areas was low in summer and high in winter. A total of 73 species representing 37 families were collected in Sacheon Bay. The dominant fish species in terms of numbers and biomass were Liparis tanakae, 23,077 inds./km2, 332.1 kg/km2. A total of 91 fish species representing 49 families were collected in coastal waters off Namhae. The dominant fish species in terms of numbers were Leiognathus nuchalis, 139,683 inds./km2 and biomass were Chelidonichthys spinosus, 1,078.6 kg/km2. Analysis of dendrogram of the clustering showed that Sacheon Bay and coastal waters off Namhae were distinctive featured (global R = 0.691, p = 0.017). And except of summer season (July-October), there was a distinctive feature seasonally (global R = 0.844, p = 0.001). The fish species that appeared in common in both areas, where fish species caught in Sacheon Bay, an important inner bay,were smaller than those caught in coastal waters off Namhae appeared. It presented that Sacheon Bay plays a more important role in spawning and nursery ground for fisheries resource than coastal waters off Namhae, Korea.

A study for species composition and abundance of the fish assemblages in the coastal Sacheon Bay, Korea were conducted using monthly collection by a shrimp beam trawl from March 2015 to February 2016. The number of individuals, biomass and species diversity indices fluctuated with the station and month. Of all 73 species collected, the dominant species in terms of numbers were Liparis tanakae, Zoarces gillii, Amblychaeturichthys hexanema, Ricuzenius pinetorum and Pleuronichys cornutus. The peak number of fishes occurred in March and April, whereas the biomass of fishes was highest in April. The numbers and biomass of fishes were lower in February corresponding with the low temperature, and diversity indices were highest in June. Due to those seasonal difference in abundance of the dominant species, fish community were divided into three main groups. In addition, seasonal difference by station of fish community were devided into four main groups. Juvenile fishes of coastal Sacheon were presented during the study period. It presented that the study area served as an important role in spawning and nursery ground for fisheries resource.

A study for species composition and abundance of the fish assemblages in the eastern Jinhae Bay, Korea was conducted using monthly larval collection by a RN80 net from October, 2010 to September, 2011. Of all the 45 species collected, the dominant species were Clupea pallasii, Hexagrammos otakii, Pholis fangi and Engraulis japonicus. Clupea pallasii, Hexagrammos otakii, Pholis fangi in winter and examined Engraulis japonicus, Acanthogobius sp., Parablennius yatabei, and Tridentiger trigonocephalus in summer appeared seasonally. Popoulation characteristic by stations was not clear seasonally and spatially, and appearance aspects of dominant species were similar by stations. Compared our results with other studies in the South Sea, dominant species and their appearance period were similar to their spawning period. Finally, the appearance period of the larvae in the South Sea was closely resulted to spawning period rather than the regional characteristic.

The feeding habits of larval (5.0~27.0 mm SL) Clupea pallasii were examined and 1,523 individuals were collected from November 2010 to March 2011 in the coastal water of Eastern Jinhae Bay, Korea. Larval C. pallasii were fed mainly on copepods that constituted 55.2% in IRI. Monogeneans were the second largest prey component, another prey items tintinnids, cladocerans and ostracoda. The results of analysis in ontogenetic changes exhibit high during the daytime, two small size classes (≤10 mm, 10~15 mm) mainly fed copepods. while the percentage of coperpods decreased, monogeneans ratio increased in 15~20 mm size class. Feeding rate in diel difference of larval C. pallasii were high during the daytime.

The feeding habits of juvenile Chaenogobius annularis were examined based on gut content analysis of 281 individuals, collected from May to June 2011 in the coastal water of Geoje, Korea. Copepods were the main source of food for C. annularis, which constituted 61.6% in IRI. Barnacle larvae was the second largest dietary component. Graphical analysis of the diet composition showed that C. annularis was a specialized predator characterized by strong individual feeding specialization. Both small and large size class of C. annularis mainly consumed harpacticoida and cirripedia cypris.

The feeding habits of yellowfin goby (Acanthogobius flavimanus) were studied based on the examination of stomach contents of 171 specimens collected from September 2013 to August 2014 in the tidal flat of Sangnae-ri, Suncheon, Korea. The size of A. flavimanus ranged from 10.6 to 18.3 cm in standard length (SL). A. flavimanus mainly consumed amphipods (especially Corophium sp.). Its diet also included shrimps, crabs, fishes and polychaetes. Ontogenetic changes in diet composition of A. flavimanus were evident. The portion of amphipods and polychaetes was inversely proprotional to the increase in fish size whereas it was directly proportional to the increase in the consumption of shrimps and crabs increased.

The diet composition of juvenile Trachurus japonicus were studied using 195 specimens collected from 2013 (May, June, July, and September) to 2014 (May, June, and July) in the coastal waters of Geumodo, Yeosu, Korea. The size of juvenile T. japonicus ranged from 4.3 to 15.2 cm in body length (BL). Juvenile T. japonicus was carnivorous and crustaceans predators that consumes mainly consumed copepods. Its diet also included small quantities of decapods, cirripedians, nematods, chaetognathans, fishes, amphipods, cumaceans, ostracods and euphausiids. The graphical method for feeding strategy revealed that juvenile T. japonicus is an opportunistic and specialized predator on copepods, especially Corycaeus. affinis, and showed narrow niche width. Juvenile T. japonicus showed ontogenetic diet change. Small size group individuals (4.3–8.0 cm BL) mainly consumed copepods. The portion of this prey item decreased in the large size group (8.0–15.2 cm BL), and this decrease was paralleled with increased consumption of decapods.

The feeding habits of Okamejei kenojei were studied using 242 specimens collected from October 2010 to September 2011 in the coastal waters of Gadeok-do, Korea. O. kenojei was carnivorous feeder that consumed mainly shrimps, crabs, and fishes. Its diet also included small quantities of stomatods, cephalopods, amphipods. The size of O. kenojei ranged from 10.4 to 47.4 cm in total length (TL). O. kenojei showed ontogenetic dietary shift. <15.0, 15.0-19.9 cm size classes fed mainly on shrimps and amphipods. 20.0-24.9 cm size class fed mainly shrimps and crabs. Thereafter, shrimps and crabs were decreased with ontogenesis while fishes and cephalopods were increased. Increasing size, the mN/ST were constantly decreased, but mW/ST were constantly increased.

During the study periods, total 143 individuals of Lateolabrax japonicus were collected. Body length (BL) range was 2.0–11.8 cm. Empty stomach occurred in 8.4%. The most abundant prey was copepods. Among copepods, Tigriopus japonicus was the most abundant prey appeared 32.1 in %F. Next important prey was shrimps and mysids. The results of analysis in ontogenetic changes, main prey of two small size classes (2.0–3.9 cm, 4.0–5.9 cm) were copepods. Thereafter, copepods percentage was decreased, but shrimps, mysids, fishes percentage was increased by increasing body length from 8.0 cm < size class.