The suitable dietary L-lysine concentration for coho salmon (Oncorhynchus kisutch) alevins was assessed by a dose response feeding trial. Six experimental diets were made with graded L-lysine concentrations of 2.29%, 2.81%, 3.32%, 3.80%, 4.27%, and 4.78% of the dry matter, respectively, each of which was fed to triplicate groups of 100 alevins (initial body weight: 0.30 ± 0.01 g) in 18 plastic baskets (water volume 240 L). The alevins were cultured in a flowing freshwater system and fed manually to apparent satiation four times a day for 12 weeks. The survival rate of alevins did not differ significantly among the dietary groups. The specific growth rate (SGR), protein efficiency ratio (PER), and body protein deposition (BPD) increased significantly (p < 0.05) with the increase in dietary lysine concentration up to 3.80% and then reduced as lysine level further increased. The feed conversion ratio (FCR) had an inverse trend to SGR. The whole-body crude protein content of the alevins increased significantly with increasing dietary lysine level, while crude lipid content showed the opposite trend. In comparison, the contents of morphological indices, whole-body moisture, and ash were not affected significantly (p > 0.05) by the different dietary lysine concentrations. The highest contents of lysine, arginine, and total essential amino acids (EAAs) were observed in the group with 4.27% dietary lysine concentration, which did not differ significantly from those in the 3.32%, 3.80%, and 4.78% groups but was significantly higher than those in the 2.29% and 2.81% groups. Similarly, valine had the highest content in the group with 4.78%. The variations in dietary lysine had no significant impacts on other EAA and non-EAA contents except glycine, which increased with increasing dietary lysine level. Second-order polynomial model analyses based on SGR, PER, BPD, and FCR evaluated the optimum L-lysine requirements of coho salmon alevins as 3.74%, 3.73%, 3.91%, and 3.77% of the diet or 6.80%, 6.78%, 7.11%, and 6.85% of dietary proteins, respectively.

The aquafeed industry relies on fish meal as a major protein source, but its use raises economic and environmental concerns, prompting the search for sustainable alternatives. This study compared the apparent digestibility coefficients (ADCs) of dry matter (DM), energy, protein, phosphorus, lipids, and amino acids (AAs) for selected protein ingredients in Coho salmon. For this purpose, one reference and seven test diets corresponding to beer yeast (BY), corn gluten meal (CGM), cottonseed meal (CSM), peanut meal (PNM), rapeseed meal (RSM), soybean meal(SBM), and soy protein concentrate (SPC) were formulated with the ratio of 70:30 of the reference diet and one of the test ingredients. 1200 fish were randomly distributed into 24 glass aquaria (each with a diameter of 3.0 m and a depth of 1.5 m, water volume 8.5 m³) with three aquaria per experimental diet (total n = 50   ^∗ 24 = 1200). The experiment lasted for 8 weeks. The results indicated that ADCs of DM ranged from 43.34% for RSM to 72.90% for SPC. Similarly, the highest ADCs of crude protein (72.69% to 86.76%), lipid (77.09% to 87.72%), and gross energy (74.12% to 55.44%) were observed in SPC, and the lowest were found in RSM. However, the ADCs of phosphorus ranged from 36.14% (RSM) to 47.35% (SBM). The ADCs of proximate nutrients for BY, CGM, PNM, SBM, and SPC were significantly higher ( p < 0.05) than other protein ingredients (RSM, CGM). Similar patterns of digestibility were observed for individual AAs of the test ingredients. Overall, the diet containing SPC appeared to be more suitable and compatible with the reference diet. Conversely, PNM, BY, SBM, and CGM showed some potential as aquafeed ingredients, whereas CSM and RSM appear to be the least viable options. Such information aids in better feed formulation by focusing on nutrient absorption rather than raw ingredient composition.

Background/Objectives: Natural bioactive compounds are promising interventions for obesity-related metabolic dysfunction. Lutein, a xanthophyll carotenoid with antioxidant and anti-inflammatory properties, may improve metabolic health, but its effects on liver function and gut microbiota in high-fat diet (HFD)-induced obesity are not fully elucidated. This study evaluated the effects of lutein supplementation on hepatic function, oxidative status, lipid metabolism, and gut microbiota composition in HFD-fed mice. Methods: Male C57BL/6J mice (6 weeks old) were randomly assigned to four groups (n = 8/group): Ctrl (low-fat diet), model (HFD), low-dose lutein (50 mg/kg/day), and high-dose lutein (100 mg/kg/day). Results: Following a 70-day intervention, lutein supplementation, particularly at the higher dose, reduced the liver index, improved serum lipid profiles, liver injury markers, and hepatic antioxidant capacity by increasing superoxide dismutase, catalase, and glutathione levels while reducing malondialdehyde content, and alleviated hepatic histopathological alterations. Lutein supplementation was also linked to elevated gut microbial richness and shifts in the relative frequency of several bacterial taxa, including partial restoration of Bacteroidota and enrichment of Roseburia and Faecalibaculum. These findings demonstrate that lutein supplementation attenuated HFD-induced metabolic and hepatic alterations, accompanied by improved antioxidant status and modulation of gut microbiota. Conclusions: Overall, lutein alleviated hepatic steatosis, oxidative stress, and metabolic dysfunction, highlighting its potential as a dietary strategy for managing obesity-related liver functions and gut dysbiosis.

High-fat diets (HFDs) can induce oxidative stress and gut microbiota imbalance, highlighting the need to explore functional dietary lipids such as red palm oil (RPO) for metabolic health improvement. This study investigated the effects of RPO intervention administered through oral gavage on growth performance, serum lipid profile, hepatic antioxidant capacity, and gut microbiota in HFD-fed mice. Compared to the high-fat control (HO) group, RPO treatment significantly reduced triglycerides (TG) and total cholesterol (TC), and increased high-density lipoprotein cholesterol (HDL-C). Furthermore, hepatic antioxidant capacity was markedly enhanced, as evidenced by improved superoxide dismutase (SOD) and catalase (CAT) activities and decreased malondialdehyde (MDA) levels in the HFD group receiving RPO. Moreover, RPO supplementation reduced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and attenuated hepatic steatosis. Gut microbiota analysis showed that RPO administration enhanced the relative abundance of beneficial bacteria while reducing potentially harmful taxa. Overall, these findings demonstrate that oral gavage of RPO can effectively alleviate HFD-induced metabolic disturbances by improving lipid metabolism, enhancing hepatic antioxidant defenses, and modulating gut microbial composition.