Since 2019, Korea Ministry of Oceans and Fisheries has set the annual total allowable catch (TAC) by fish species, and has allocated the annual TAC into each fishery vessel. Also the Korea government plans to adopt the individual transferrable quota system in time. The TAC allocation is similar to the individual fishermen/fishing quota, which the US National Oceanic and Atmospheric Administration has implemented. However, the TAC based management faced fishermen's complaints and a debate is still underway about how to allocate TAC. Because the ideas of the Korea policy are from those in the foreign countries, I intended to provide the Korea fisheries community with an overview about how the TAC has been developed, what problem it caused, and foreign examples of how to allocate it. Furthermore, I pointed out a substantial room for improvement in their current practice of stock assessments, because, otherwise, their current methods for estimation of TAC by species cannot be trusted. Finally I made specific suggestions about what they need to do to reform their current stock assessments.

Boil-dried concentrate (BDC) and steam-dried concentrate (SDC) were prepared from olive flounder Paralichthys olivaceus roe using the cook-dried process, and their food functionality and in vitro bioactivity were examined. The buffer capacity of BDC and SDC was found to be stronger in the alkaline region than in the acidic region, and the buffer capacity of SDC was superior to that of BDC. The water holding capacities of these concentrates were 7.6 and 7.4 g/g protein, respectively, both of which were significantly lower than that of freeze-dried concentrate (FDC). The solubility of BDC (13.4%) and SDC (12.7%), foaming capacity of BDC (107.7%) and SDC (110.6%), and oil-in-water emulsifying activity index of BDC (7.7 m²/g) and SDC (9.7 m²/g) were all significantly lower than the corresponding values for FDC (P<0.05). The lower food functionality of BDC and SDC compared with FDC can be attributed to the high-temperature denaturation of proteins during the cook-dried process. The 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical scavenging activities (IC₅₀) of SDC (2.5 mg protein/mL) was 60.4 ㎍/mL, and the angiotensin I converting enzyme inhibitory activity was 80.9%. Olive flounder roe concentrates have good antioxidant and antihypertensive activities, and can be used as materials or ingredients in the processing of seafood and other foods to enhance protein contents and food functionality.

Lotus Nelumbo nucifera seed protein (LSP) was isolated by alkaline solubilization after removing fat and phenolics by hexane and ethanol treatment. Antioxidant peptides from LSP were produced with Alcalase^® and pepsin and hydroxyl radical scavenging activities were determined. LSP-Alcalase^® hydrolysates showed higher hydroxyl radical scavenging activity than LSP-pepsin hydrolysates. To purify antioxidant peptides, LSP-Alcalase^® hydrolysates were subjected to high performance liquid chromatography (HPLC) separation on the C18 column and the active fraction was further purified using a Superdex^TM peptide 10/300 GL column. Finally, the active fraction (F8-2) was evaluated for antioxidant activities by 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl radical scavenging, and oxygen radical absorbance capacity (ORAC) assays. The EC₅₀ values of the F8-2 were 105.81±0.02 ㎍/mL for DPPH and 32.26±0.02 ㎍/mL for hydroxyl radical and the F8-2 exhibited 7.22 μM trolox equivalent (TE)/100 ㎍ F8-2. Glutathione (GSH), which is a positive control, showed EC₅₀ values of 19.87±0.01 ㎍/mL for DPPH and 15.95±0.03 ㎍/mL for hydroxyl radical and an ORAC value of 14.17±0.03 μM TE/100 ㎍ GSH. Finally, sixteen peptides were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Among them, Ile-Tyr and Leu-Tyr showed higher antioxidant scores.

We optimized ultrasound-assisted extraction to improve the extraction efficiency of bioactive compounds from the microalgae Acutodesmus reginae. To optimize this extraction process, we investigated the effects of solvent type, solvent concentration, extraction time, extraction number, and extraction power on the production of lutein, α-carotene, β-carotene, and chlorophylls a, and b. After sequential optimization of these main variables, the maximum amount of each compound was extracted at 30℃ with an ultrasound power of 80 W and using 99.5% methanol. Under these optimum conditions, the amount of lutein, α-carotene, β-carotene, and chlorophylls a, and b, were measured as 10.43, 8.66, 3.76, 15.43, and 6.39 mg/g dry matter respectively.

This study compared the nutritional composition of rainbow trout Oncorhynchus mykiss from different inland-based trout farms. The proximate composition ranges of the fish were 67.10-72.77 g/100 g moisture, 19.13-21.35 g/100 g crude protein, 5.12-11.72 g/100 g crude lipid, and 1.24-1.97 g/100 g ash. In addition, rainbow trout contained significantly different mono- and poly-unsaturated fatty acid concentrations, ranging from 1.31 to 4.33 g/100 g and 1.21 to 3.2 g/100 g, respectively. The content of n-3 and n-6 fatty acids ranged from 0.68 to 1.68 and from 0.49 to 1.61 g/100 g, respectively. The n-6/n-3 ratio was in the range of 0.79-1.59. The vitamin content of the rainbow trout from the different farms was 14.83-49.30 ㎍/100 g vitamin A, 922.05-3,179.38 ㎍/100 g alpha-tocopherol, ND-73.59 ㎍/100 g, gamma-tocopherol, 2.97-14.55 ㎍/100 g vitamin D, and 76.63-126.03 ㎍/100 g vitamin B₂. Slight differences were observed in the crude lipid, fatty acid, and vitamins A and E contents among the of rainbow trouts from the different farms. The results suggest that the fish nutrient composition, especially that of lipids, was significantly different among rainbow trouts from different farms, but may not be related to the production area.

In this study, the morphological development and early life cycle of larvae and juvenile Rhinogobius brunneus found in Wicheon, Nakdong River, Korea, were investigated. The fertilized eggs were 2.20×0.68 mm (long×short) in diameter. The eggs began hatching approximately 104 h after fertilization at water temperatures of 17.3-20.5℃ (mean 18.9±1.6℃). The newly hatched yolk-sac larvae were 3.71±0.06 mm in total length (TL), with an unopened anus. Three days after hatching, the preflexion larvae were 4.37±0.16 mm in TL with yolk absorption. Twenty days after hatching, the flexion larvae were 6.50±0.22 mm in TL and the tip of the notochord was bent upward. Twenty-seven days after hatching, the postflexion larvae were 11.8±0.63 mm in TL, and the tip of the urostyle was bent at 45°. Forty days after hatching, individuals measured 18.5±0.93 mm in TL and were considered as juveniles as the number of fins became constant for each part. All the postflexion larvae had detached fins. Additionally, the melanophore was observed to be distributed on the head, centrum of the body, and dorsal fin, and there was a difference in the morphology from the water stream.

Effect of environmental factors on the seasonal variations of zooplankton communities was investigated in the semi-closed Yeoja Bay, Korea from February, April to August, and November 2021. Out of a total 49 species of zooplankton were collected with a predominant of neritic copepods (mainly Paracalanus orientalis, Acartia omorii, Acartia ohtsukai, Centropages abdominalis, Ditrichocorycaeus affinis, and Oithona sp.), accounting for 58.9% of the total abundance of zooplankton. The diversity indices indicated a relatively highest in July, suggesting that diversity is influenced by seasonal temperature, N. scintillans, and neritic copepods species. A cluster analysis with non-metric multidimensional scaling revealed four groups of zooplankton communities. The February sample clustered into Group A, having the lowest mean total abundance and species diversity of zooplankton, consisting mainly of N. scintillans located the whole region. Cluster Group B from the spring season (April to May) and contained the species diversity with some neritic copepods. Cluster Group C from the summer season (June to August) mainly comprised P. orientalis, A. ohtsukai, Oithona sp., and hydromedusae. Cluster Group D from the autumn season (November) mainly comprised P. orientalis, Temora discaudata. Redundancy analysis indicated that abundance is positively correlated with temperature, salinity, and pico chlorophyll-a concentrations. This study showed that planktonic larvae (such as branchyura larvae) and some copepods (including A. omorii, A. ohtsukai, C. sinicus, and C. abdominalis) were significantly vulnerable to zooplankton community of temperature, salinity, and pico chlorophyll-a concentrations.

The sea hare Aplysia kurodai is an economic species located along the Korean coast. This study aimed to investigate the stomach contents of A. kurodai and its relationship with marine algal flora surrounding their habitat. A. kurodai and marine algae were sampled in seven and five areas in the East and the South seas, respectively. The marine algae found in the stomach and surrounding marine habitat were identified. In the East Sea of Korea, 134 species of seaweed were recorded. Thirty-nine species of marine algae were identified in the stomach contents of A. korudai collected from the East Sea of Korea. Seventy-five species of seaweed were collected in the South Sea of Korea. In addition, 26 species of marine algae were identified in the stomach contents of A. kurodai from the South Sea of Korea. Among the stomach contents of A. kurodai, ten sheet,12 filamentous, 27 coarsely branched, and one jointed calcareous form species were identified.

A 12-week feeding trial was conducted to evaluate the effect of different stocking densities on the growth, body composition, stress, antioxidant status, and immune responses of juvenile rainbow trout Oncorhynchus mykiss. Juvenile rainbow trout (32.2±0.5 g) were randomly placed in eight experimental tanks, each containing 2,000 L of water, at stocking densities of 150, 300, 600, and 1,200 individual/m³. The trout were assigned to four treatments (2.4, 4.8, 9.7, and 19.4 kg/m³) in duplicates. Following after the feeding trial, the fish cultured in the less dense group showed significantly higher growth and survival (P<0.05). In terms of proximate composition, the whole body crude protein and lipid contents were lower in the denser group (19.4 kg/m³). Regarding the antioxidant and immune responses, the fish reared in the relatively denser group exhibited lower lysozyme, immunoglobulin M, and superoxide dismutase levels. The stress indicators, glucose and cortisol, were significantly lower in the less dense group (2.4 kg/m³), while the denser group (19.4 km/m³) exhibited higher AST and ALP levels(P<0.05). The results showed that denser stocking has a crowding stress effect and negatively impacts growth and immune responses.

We evaluated the effects of prebiotic (mannan oligosaccharides, Mos) and probiotic diet supplements on growth performance, innate immunity, antioxidant activity, and intestinal changes in the microbial flora of red seabream Pagrus major. A basal diet (Con) was formulated to meet the nutrient requirement of red seabream. The dietary starch in Con was replaced with 0.6% Mos, Lactobacillus plantarum, Bacillus subtilis, B. licheniformis and probiotic mixture (labeled as Mos, Pro-LP, Pro-BS, Pro-BL and Pro-Mix, respectively). We stocked 450 fish in 18 polypropylene tanks (400 L) in triplicate groups per dietary treatment. The fish were fed one of the diets twice (08:30, 18:30 h) a day for 63 days. Lysozyme activity was significantly higher in all the supplemented groups than that of the Con group. The immunoglobulin level of Pro-Mix, anti-protease activity of Pro-BL, and glutathione peroxidase and superoxide dismutase activity of Pro-BS, Pro-BL and Pro-Mix groups were significantly higher than those of the Con group. The ratio of total Vibrio/heterotrophic marine bacteria counts was significantly lower in Pro-LP, Pro-BL and Pro-Mix groups than that of the Con group. Therefore, dietary supplementation of Mos and probiotics to improves immune response and antioxidant enzyme activity and inhibits Vibrio bacteria in the intestine.

In this study, changes in biofloc-related and pathogenic bacteria in both low and high concentration biofloc breeding water planted with the halophyte (Triglochin maritimum were investigated). In the low-concentration biofloc breeding water, the ratio of bacteria related to the nitrogen cycle was initially 59.57% and, it decreased to 26.57% at the end of the experiment while other bacteria (excluding nitrogen-cycling bacteria and vibrios) increased from 38.75% to 73.43%. However, the planted experimental group maintained a relatively high ratio of nitrogen cycling bacteria at 58%. In the high-concentration experimental group, bacteria related to the initial nitrogen cycle, non-pathogenic vibrios, and pathogenic vibrios were 11.60, 36.28, and 20.14%, respectively. Finally, nitrogen-cycling bacteria were 36.47% in the control group and 37.55% in the planted group. The total number of vibrios decreased by 46.54% in the planted group and 48.01% in the control group, indicating a significant decrease in both experimental groups. However, the residual rate of pathogenic vibrios was 4.48% in the control group and 0.54% in the planted group. Overall, the planted group showed decreasing harmful bacteria and increasing useful bacteria.

Interspecific hybridization is a beneficial strategy in aquaculture. In this study, diploid hybrids were produced through interspecies hybridization of flounder Platichthys bicoloratus ♀ × starry flounder P. stellatus ♂, which became commercial within a year. These hybrids exhibited an advantage in growth ability, with female hybrids growing twice as large as males at 11 months. Furthermore, hybrid flounders exhibited faster growth rates than starry flounders and reciprocal hybrids. The average growth rate of hybrids was 1.37 and 1.18 times greater than that of starry flounder and reciprocal hybrids at 5.5 months, respectively; Additionally, feed efficiency was 1.21 and 1.10 times higher than that of the experimental groups. The experiments were conducted at five temperatures to determine the optimal fry production method. Six weeks of culture resulted in a significant temperature effect, with maximum growth at 27℃. However, over 90% of the males occurred in the groups at temperatures above 24℃. Therefore, the optimum temperatures for survival, growth, condition factor and frequency of the best-sized fingerling at 13 weeks of age were estimated at 21℃. Thus, hybrid flounders are of great potential for use in the flounder aquaculture industry.

Flow-through aquaculture systems generate large amounts of wastewater containing compounds such as solids that can settle near aquafarms and cause eutrophication. The settled solids are often reintroduced into flow-through systems, and aquatic animals can be affected by the solids and pathogens associated with these solids. For a sustainable aquaculture operation, adequate wastewater treatment is required. Hydrocyclones are one of the most promising technologies for the removal of solids in aquaculture wastewater. In this study, a model for performance prediction of hydrocyclones was investigated under three different operating conditions: water temperature, solids concentration, and water inlet velocity. The synthetic solids solution was prepared using settled solids from abalone aquaculture farms. The daily solids removal rates of the tested hydrocyclones ranged from 0.18 to 26.0 g solids-m^-3-day^-1, and removal efficiency ranged from 5.1 to 34.4%. The inlet water velocity had the greatest effect on solids removal and hydrocyclone efficiencies. The following multiregression model equation was derived from the daily solids removal rate (g solids-m^-3-day^-1) results for water temperature (T, ℃), solids concentration (SS, mg-L^-1), and tangential inlet water velocity (TIV, m-sec^-1): daily solids removal rate: f(z)=4.465+0.809TIV-0.375T+0.217SS (r²=0.976).

This study aimed to cross between Korean and Japanese pure lines of Neopyropia strains to establish cross breeding technology and identify a superior variety that harbors the strength of both parents. Four crossing combinations were tried using three methods, resulting in 1,476 single conchocelis colonies. The three co-dominant Cleaved Amplified Polymorphic Sequence (CAPS) markers (EF-1α/Mse I, TOP2/Mse I, car A/ApaL I) were used to distinguish heterozygotic sporophytes and their maternal lines obtained from the inter and intraspecific cross-fertilization within the wild type of Neopyropia strains. Of the 1,476 colonies, 26.9% (218) were heterozygotes obtained from the nuclear CAPS markers. Their maternal line was clearly confirmed using organelle CAPS marker and chimeric thallus was obtained from crossing experiment of Japanese N. yezoensis (♀) and Korean N. yezoensis (♂). The use of CAPS markers improved the efficiency of crossbreeding by quickly screening heterozygotes and maternal lines in the conchocelis phase, which otherwise required pigmentation mutants as genetic markers.

The advantage of biofloc technology (BFT) in aquaculture is in the prevention of pathogenic transmission. In this study, we performed an investigation on viral, bacterial, and microsporidian parasite infections targeting a total of 194 whiteleg shrimp Litopenaeus vannamei reared in seven BFT-farms on the west coast of Korea in 2021. Hepatopancreatic and cuticular epithelium and pereiopods tissues of shrimp were tested for the four pathogens, Enterocytozoon hepatopenaei (EHP), Vibrio parahaemolyticus causing Acute Hepatopancreatic necrosis disease (VP_AHPND), white spot syndrome virus (WSSV), and hepatopancreatic parvovirus (HPV). The microsporidian parasite EHP was detected in the hepatopancreatic tissue of BFT whiteleg shrimp in the Ganghwa region, whereas no other pathogenic bacteria or virus was detected on the shrimp in the seven BFT-farms. As a result of bacterial flora in the rearing water of BFT whiteleg shrimp using DNA microbiome technology, V. chemaguriensis and V. alfacsensis were contained at 0.05% and 0.01%, respectively, but no VP_AHPND was detected. These findings will serve as a basis for supporting safe BFT-aquaculture of whiteleg shrimp.