This study aimed to improve the nutritional value of Sargassum horneri (SH) and evaluate its effect on rumen fermentation characteristics and greenhouse gas emissions. The first trial estimated the effects of blanching temperatures (21, 60, 70, and 80 °C) and durations (1, 2, and 3 min) on the chemical and mineral content of SH. The second trial evaluated the effects of SH supplementation levels (0, 1, 3, and 5%) and blanching temperatures (21 and 70 °C) on in vitro rumen fermentation characteristics and greenhouse gas emissions. As the blanching temperature and time increased, the dry matter and crude ash content decreased (p < 0.05), and the ether extract, neutral detergent fiber, and acid detergent fiber content increased (p < 0.05). There were significant reductions in Na, K, and As (p < 0.01) when the blanching temperatures increased. As the SH supplementation levels increased, in vitro digestibility of both dry and organic matter decreased (p < 0.001) and the methane production reduced (p < 0.001). Therefore, this study shows that blanching SH at 70 °C for 3 min optimized its nutritional value and improved its potential as a feed source that has methane mitigation characteristics at 3 to 5% supplementation levels.

Chemokines is a small protein that plays a major role in inflammatory reactions and viral infections as a chemotactic factor of cytokines involved in innate immunity. Most of the chemokines belong to the chemokine groups CC and CXC. To investigate the immune system of the olive flounder (Paralichthys olivaceus), an expression pattern specifically induced in the early developmental stages of analysis is examined using qRT-PCR. We also examined tissue-specific expression of both CC and CXC chemokine in healthy olive flounder samples. CC and CXC chemokine shows increased expression after immune-related organs are formed compared to expression during early development. CC chemokine was more highly expressed in the fin, but CXC chemokine showed higher expression in the gills, spleen, intestines, and stomach. Spatial and temporal expression analysis of CC and CXC chemokine were performed following viral hemorrhagic septicemia virus (VHSV) infection. CC chemokine showed high expression in the gills, which are respiratory organs, whereas CXC chemokine was more highly expressed in the kidneys, an immune-related organ. These results suggest that CC and CXC chemokine play an important role in the immune response of the olive flounder, and may be used as basic data for the immunological activity and gene analysis of it as well as other fish.

Numerous studies have explored alternative protein sources to fishmeal (FM) to enhance fish diets, yet limited research exists on their effects on maturation. This study assessed the impact of replacing FM with soy protein concentrate (SPC) supplemented with lysine and methionine on growth and gonadal development in olive flounder (Paralichthys olivaceus). Three diets were tested: a control (Con) diet with 60% FM and two diets replacing FM with 25% (LF1) and 50% (LF2) SPC. Fish were fed to apparent satiation twice daily for 12 months. Growth performance and feed intake were not significantly different between groups. However, the gonadosomatic index varied with diet. Muscle composition and amino acid levels were similar across treatments, though n-3 fatty acids were higher in Con. Spermatogonia was increased, and spermatogenesis was impaired in SPC groups. At 12 months, oocytes in Con diets had absorbed yolk globules, whereas this was absent in SPC groups. Growth-related genes in the brain (growth hormones and insulin-like growth factor) were increased with higher SPC, while follicle-stimulating and luteinizing hormones decreased. Estrogen receptor α levels were elevated in SPC groups. Vitellogenin gene expression in gonads was highest in Con, while liver expression peaked in LF2. The expression of digestive enzymes, chymotrypsin2, and trypsin2 was highest in LF2, while lipase genes were lower. In summary, up to 50% FM replacement with SPC, with amino acid supplementation, supported growth performance and muscle composition without adverse effects on growth in olive flounder but influenced gonadal development.

The rock bream Oplegnathus fasciatus belongs to the family Oplegnathidae and is widely distributed in the Indian and Pacific Oceans, including Korea, Japan, Taiwan, and Hawaii. Adults inhabit coastal rocky reefs, while juveniles associate with drifting seaweed and feed on zooplankton. It is an economically important resource in the fishing industry in Korea (Oh et al., 2007; Lee et al., 2016). Due to the rapid development of the aquaculture industry in recent years, the spread of bacterial and viral diseases has resulted in economic losses, including massive losses and reductions in productivity (Jung & Oh, 2000; Lee et al., 2016).

This study identified the effects of substituting fishmeal (FM) with soy protein concentrate (SPC) supplemented with lysine and methionine in the olive flounder (Paralichthys olivaceus) diet on the expression of genes related to growth, stress, immunity, and digestion. Three experimental diets were prepared; the control diet (Con) contained 60% FM, and the experimental diets contained 25% (SPC25) and 50% (SPC50) FM replaced by SPC. After the 140-day feeding period, weight gain, specific growth rate, feed availability, biological indices, and chemical composition of the muscle were not significantly affected by the dietary treatments. The gene expression levels of growth-related genes (IGF, GFB-3), immune-related genes (IL-8 and caspase), and stress-related genes (SOD, GPX, PRX, TRX) were higher in Con fish than in those fed the SPC25 and SPC50 diets. Chymo-TRY2, TRY2, and TRY3 in the stomach of fish fed the SPC25 diet were higher than fish fed the Con or SPC50 diets. TRY2 and lipase of fish fed the SPC25 diet were higher than those of fish fed the other diets but TRY3 was not significantly affected by the treatments in the intestine. In conclusion, substituting 25% FM with SPC was the most effective diet for the expression of growth, immune, stress, and digestive enzyme genes.

This study investigated the genetic diversity and structure of thirteen wild populations of Crassostrea gigas in Korea. The purpose of this investigation was to provide foundational data for selecting reference populations to enhance genetic diversity. Overall, the genetic diversity of Korean C. gigas was relatively low. Analysis using AMOVA, genetic differentiation, and DAPC revealed a genetic structure that was consistent with one group. This study identified reference populations to be used for selective breeding to increase the genetic diversity of Korean C. gigas and provided essential data on genetic diversity and structure for future selective breeding efforts in C. gigas.