Byung Hwa Min

The hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus) is a high-value aquaculture species with limited cold tolerance in temperate regions such as South Korea. Two complementary temperature experiments were conducted. In Experiment I, smaller juveniles (33.9 ± 10.2 g) were subjected to water temperatures (20, 18, 16, 14, and 12 °C) lower than 27 °C for 30 days to assess survival. In Experiment II, larger juveniles (281.1 ± 2.9 g) were reared for 90 days at 27, 24, 21, 18, and 15 °C to evaluate chronic physiological responses; brain and liver RNA-Seq analyses compared the 15 °C low-temperature condition with the 27 °C control condition. Fish maintained at 15 °C exhibited progressive mortality, whereas fish reared at 18–27 °C showed 100% survival during the 90-day trial. Exposure to 15 °C was associated with significant decreases in hemoglobin and hematocrit, a >5-fold increase in plasma cortisol, and elevated glucose levels. SOD and CAT activities were also elevated at low temperatures, indicating an enhanced antioxidant response; however, these enzyme measurements do not directly quantify reactive oxygen species. Transcriptomic profiling revealed temperature-associated expression differences, with more DEGs in the liver (1365) than in the brain (221). Brain DEGs were associated with calcium-signaling- and neural-related categories, whereas liver DEGs were associated with metabolic, antioxidant response, and extracellular-matrix-related categories. Functional enrichment findings that did not meet FDR < 0.05 were treated as suggestive or exploratory rather than statistically significant. These findings help define the lower thermal tolerance of hybrid grouper and provide information relevant to aquaculture management under low-temperature conditions.

This study evaluated the optimal dietary lipid level for Atlantic salmon (Salmo salar) reared in freshwater, aiming to provide foundational knowledge for the development of cost-effective and nutritionally balanced aquafeeds. Four experimental diets were formulated to contain comparable crude protein levels (47%) but graded lipid levels of 14% (L14), 16% (L16), 18% (L18), and 20% (L20), and were fed to salmon with an initial mean body weight of 241.5 ± 9.7 g during a 12-week feeding trial. Fish in the L16 group exhibited the highest weight gain (WG) and feed efficiency (FE), whereas those in the L14 group showed significantly reduced growth performance. Antioxidant analysis revealed that glutathione peroxidase (GPx) activity was lowest in the L14 group (p < 0.05), while plasma glucose concentration was minimized in the L16 group (p < 0.05). Transcriptomic profiling of liver tissue from the L14 and L16 groups identified 2117 differentially expressed genes (DEGs). Genes associated with lipid metabolism were more highly expressed in the L16 group, whereas immune- and inflammation-related genes were upregulated in the L14 group. These findings suggest that a dietary lipid level of approximately 16% is most favorable for promoting growth, metabolic stability, and overall health in freshwater-reared Atlantic salmon, thereby providing practical guidance for optimizing feed formulation and improving the economic efficiency of freshwater salmon aquaculture.

This study evaluated the effects of partially replacing fish meal (FM) with a balanced mixture of poultry byproduct meal (PBM) and soy protein concentrate (SPC) on the growth, physiological responses, and economic performance of Atlantic salmon ( Salmo salar ) post‐smolts reared in a recirculating aquaculture system (RAS). In total, four extruded diets were tested for 12 weeks: two experimental formulations—high‐FM control, experimental diet (ED)1; 25% FM replaced with PBM + SPC, ED2—and two commercial reference feeds. Growth performance, feed efficiency (FE), and survival were statistically comparable across treatments, indicating that PBM–SPC inclusion did not compromise nutrient utilization. The proximate composition, amino acid (AA) profile, and lipid deposition in fish stabilized. The PBM–SPC diet maintained a favorable n‐3/n‐6 fatty acid (FA) ratio and a high retention of eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) comparable to FM‐based feeds. Plasma biochemical indices and digestive enzyme activities were unaffected, demonstrating normal hepatic and metabolic function. Among diets, plasma antioxidant enzyme activities and serum lysozyme levels were similar, suggesting a maintenance of oxidative stress and immune balance. Expression of hepatic genes interleukin‐1 beta ( IL-1β ), tumor necrosis factor‐alpha ( TNF-α ), IL-10 , FA synthetase ( FAS ), and peroxisome proliferator‐activated receptor α ( PPARα ) confirmed that the PBM–SPC diet did not trigger any inflammatory or metabolic stress. However, histology revealed normal liver and intestinal morphology without signs of steatosis or enteritis. The PBM–SPC diet reduced feed costs and achieved a lower economic conversion ratio (ECR) while maintaining profitability equivalent to or greater than commercial feeds. Overall, the results demonstrate that partial substitution (25%) of FM with PBM and SPC sustains optimal growth, physiological stability, and economic efficiency of post‐smolt S . salar under RAS conditions.

Rochia nilotica is a tropical Pacific gastropod inhabiting shallow coral reef habitats and supporting important marine resources in Pacific island nations. In this study, we analyzed specimens collected from Weno Island, Chuuk Atoll, Federation States of Micronesia (FSM), using an integrative approach that combined morphological characteristics, molecular phylogenetics (COX1 and 16S rRNA), and complete mitochondrial genome analysis. While the Chuuk population exhibited morphological features consistent with R. nilotica, molecular data revealed substantial genetic divergence. Phylogenetic analyses based on the complete mitochondrial genome (17,664 bp) clustered the Chuuk specimen with Rochia virgata. Phylogenies inferred from concatenated COX1 and 16S rRNA gene sequences yielded congruent topologies, placing the Chuuk lineage within the Rochia clade but clearly separated from other R. nilotica populations in New Caledonia and Mo’orea Island, French Polynesia. This genetic divergence is likely driven by the long-term geographic isolation of Chuuk Atoll. The lagoon’s fringing reefs descend rapidly into waters exceeding 4000 m, which may act as a barrier to restricting larval dispersal. Combined with the extremely short planktonic larval duration of R. nilotica (approximately four days), such environmental isolation may promote the formation of a distinct gene pool. Despite morphological uniformity, the observed genetic divergence suggests that the Chuuk population may represent a cryptic species. Our study provides a complete mitochondrial genome and offers robust phylogenetic framework that provides an understanding of species boundaries within Rochia. These findings underscore the importance of integrating genomic and morphological data for accurate species identification and have implications for conservation and sustainable aquaculture practices in geographically isolated reef ecosystems.

The drastic surge in Sardine landings in Korea underscores the urgent need for sustainable upcycling strategies. However, research on the feasibility of using sardine (SD) in food waste (FW)-based substrates during the cultivation of black soldier fly (Hermetia illucens) larvae (BSFL) remains limited. Thus, we aimed to investigate the effect of incorporating varying SD contents (0, 25, 50, 75, and 100%), into which 4-day-old (third-instar) larvae weighing approximately 0.02 g were introduced and reared for 12 days in triplicate. SD inclusion in the substrate had a dose-dependent effect on BSFL growth; higher concentrations (≥50%) markedly inhibited key growth indices, including a significant reduction in total biomass (p < 0.05). Incorporating SD into the diet dose-dependently enriched the biomass with eicosapentaenoic acid and docosahexaenoic acid while reducing the relative proportions of saturated and monounsaturated fatty acids (p < 0.05). Proteobacteria and Firmicutes were the dominant phyla in the intestinal microbiota of BSFL. Further, SD inclusion altered the gut microbial community structure. Increased SD concentration in the diet led to a progressive reduction in unique genera, indicating decreased microbial diversity at higher inclusion levels. Overall, incorporating SD into FW for BSFL cultivation is feasible; however, optimizing substrate composition—particularly moisture and nutrient balance—is necessary to enhance larval growth and productivity.

Feeding is among the most labor-intensive tasks in aquaculture, yet it is critical for productivity and operational efficiency. Although automated feeding systems reduce labor, the absence of data on optimal pellet size, feeding rate, and frequency has led to inconsistent practices and productivity. We evaluated the applicability of a low-cost automatic feeder and determined optimal pellet size and feeding frequency for juvenile olive flounder (Paralichthys olivaceus) in an experiment where 600 fish (83.4 ± 0.7 g (mean ± SD)) were randomly assigned to 12 flow-through tanks (60 fish/tank) in triplicate. In Experiment 1, fish fed 5-mm pellets presented greater weight gain and protein efficiency ratio (PER) than those fed 3-mm pellets (p < 0.05). In Experiment 2, manual feeding was compared to automatic feeding. Fish fed three times per day at a 1.3% daily feed intake (DFI) achieved similar growth but an improved feed conversion ratio and PER compared to manually fed fish (p < 0.05). Our findings support the use of 5-mm pellets at 1.3% DFI with a low-cost automatic feeder for maintaining productive juvenile flounder. These results present a practical automation strategy that enables small and medium-sized aqua-farms to reduce labor while maintaining productivity equivalent to manual feeding.

Groupers (Epinephelidae, Pisces: Perciformes) are a tropical and subtropical marine fish comprised of 16 genera and 163 species (Craig et al., 2011), and are commercially valuable in Asian live fish markets (FAO, 2017; Rimmer & Glamuzina, 2019). The sexual characteristics of Epinephelidae are complex and diverse and classified as gonochorism, protogynous hermaphroditism, and bi-directional sex change (Sadovy de Mitcheson & Liu, 2008; Liu et al., 2016).