The present study investigated the effects of dietary riboflavin on growth performance, body composition and anti-oxidative capacity of coho salmon (Oncorhynchus kisutch) post-smolts. Seven experimental diets were formulated with graded riboflavin levels of 0.00, 3.96, 8.07, 16.11, 31.81, 63.67 and 126.69 mg/kg, respectively. Each diet was fed to triplicate groups of 10 fish with an individually initial mean body weight of 186.22 ± 0.41 g in 21 cages (water volume, 1000-L/cage) and fed three times daily (7:30, 12:30 and 17:30) to apparent satiation for 12 weeks. Fish fed a diet with 31.81 mg/kg riboflavin had the highest specific growth rate (SGR), which was significantly higher than fish-fed diets with 0.00, 3.96, 8.07 and 126.69 mg/kg riboflavin (p < 0.05). Feed conversion ratio showed an inverse trend with SGR. No significant differences were observed in condition factor, hepatosomatic index, viscerosomatic index, muscle moisture, crude protein and ash contents among dietary groups. Muscle lipid had the highest content in the 31.81 mg/kg group and was significantly higher (p < 0.05) than those in the 0.00, 3.96 and 8.07 mg/kg groups. The alanine aminotransferase, aspartate aminotransferase and malondialdehyde contents in the liver and serum of fish were significantly decreased with the increase in dietary riboflavin level up to 31.81 mg/kg, and then increased as dietary riboflavin level further increased. An inverse trend was observed for total superoxide dismutase and catalase activities. Serum total cholesterol and triglyceride levels were significantly decreased with the dietary of riboflavin levels up to 31.81 and 63.67 mg/kg, respectively. The cubic curve regression analysis based on SGR indicated that the optimum dietary riboflavin level was estimated to be 35.26 mg/kg for coho salmon post-smolts.

A 12-week feeding trial aimed to evaluate the effects of dietary linoleic acid (LA, 18:2n-6) on the growth performance, fatty acid profile, and lipid metabolism enzyme activities of coho salmon (Oncorhynchus kisutch) alevins. Six experimental diets (47% crude protein and 15% crude lipid) were formulated to contain graded LA levels of 0.11%, 0.74%, 1.37%, 2.00%, 2.63%, and 3.26%. Each diet was fed to triplicate groups of 50 alevins with an initial body weight of 0.364 ± 0.002 g, which were randomly assigned to 18 white plastic tanks (0.8 × 0.6 × 0.6 m, 240 L/tank). Fish were reared in a freshwater flow-through rearing system and fed to apparent satiation four times daily. The survival rate was not significantly different among the treatments (p > 0.05). However, the 1.37% LA group significantly improved the final body weight and specific growth rate (SGR) (p < 0.05) of alevins. The feed conversion ratio (FCR) in the 1.37% LA group was significantly lower than those in other groups (p < 0.05). The whole-body lipid content significantly decreased (p < 0.05) with dietary LA levels increasing from 0.74% to 2.00%. The fatty acid composition of the total lipid in muscle was closely correlated with those in the diets. The dietary LA level of 1.37% led to significantly higher activities of liver lipoprotein lipase (LPL) and hepatic lipase (HL) than those of other groups (p < 0.05). Hepatic malate dehydrogenase (MDH) and fatty acid synthase (FAS) decreased with the increase in the dietary LA levels from 0.11% to 1.37%. The lowest MDH and FAS activities were obtained in the 1.37% LA group (p < 0.05). This study indicated that an appropriate amount of dietary LA was beneficial for the growth and lipid metabolism of coho salmon alevins, and the results of the quadratic regression analysis of the SGR and FCR indicated that the optimal dietary LA requirements were 1.25% and 1.23% for coho salmon alevins, respectively.

The present study evaluated the effects of supplemental dietary α-linolenic acid (ALA, 18:3n-3) on growth performance, body composition, hepatic fat metabolizing enzymes, and fatty acid profiles of coho salmon (Oncorhynchus kisutch) alevins cultured in freshwater. Six isonitrogenous and isolipidic experimental diets were formulated to attain different levels of ALA (0.09, 0.41, 0.76, 1.03, 1.32, and 1.68% dry weight) by adding linseed oil in a basal diet, respectively. Each diet was fed to triplicate groups of alevins (50 fish in each tank) with initial mean body weight of 0.352 ± 0.002 g. Fish were reared in a freshwater flow-through rearing system and fed to apparent satiation 4 times daily for 12 weeks. The specific growth rate (SGR) increased with increasing dietary ALA level, which reached the peak at 1.03% ALA group ( ). The final body weight (FBW) and SGR showed linear, quadratic, and cubic responses with the dietary ALA level. The whole-body crude protein increased with increasing dietary ALA level while lipid content was the opposite trend ( ). However, the content of crude lipid in the whole-body of fish showed quadratic and cubic responses with the dietary ALA level. In addition, except for fatty acid synthase (FAS), the hepatic enzymes activities of lipoprotein lipase (LPL), hepatic lipase (HL), and malate dehydrogenase (MDH) showed linear, quadratic, and cubic response with the dietary ALA level ( ) The activities of hepatic LPL and HL in 1.32% ALA group were significantly higher than other groups ( ). The activities of hepatic MDH and FAS in 1.32% ALA group were the lowest, which were significantly lower than those in ALA groups (form 0.09% to1.03%) ( ). Except for the content of MUFA, the contents of other fatty acids showed linear, quadratic, and cubic response with the dietary ALA level. The ALA and ∑n-3 PUFA content significantly increased with increasing dietary ALA levels ( ). These results indicated that dietary ALA actively impacted fish growth performance, hepatic lipid metabolizing enzymes, and muscle fatty acid profile. The cubic regression analysis based on SGR as evaluation indices indicated that the optimal dietary ALA content was 1.33% dry weight of diet for alevins.

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 present study determined the apparent digestibility coefficients (ADCs) of dry matter, nutrients, and energy in selected seven animal protein ingredients, including Peruvian fish meal (PFM), native fish meal (NFM), Antarctic krill meal (AKM), native shrimp meal (NSM), poultry by‐product meal (PBPM), meat and bone meal (MBM), and hydrolyzed feather meal (HFM) for coho salmon ( Oncorhynchus kisutch ) post‐smolts (initial body weight: 212.73 ± 5.15 g). Using yttrium oxide (Y ₂ O ₃ , 0.5 g/kg) as an inert marker, a reference diet was formulated to contain ~440 g/kg of crude protein and 200 g/kg of crude lipid, whereas the test diets were composed of the reference diet and one of the test ingredients at a ratio of 70:30. The dry matter ADCs of the test animal protein ingredients ranged from 65.14% to 83.77%. The ADC of energy followed a similar trend to that of dry matter (69.03%–87.52%). The crude protein and lipid in all the test ingredients were well digested by the post‐smolts with ADCs ranging from 74.12% to 91.67% and 75.44% to 92.38%, respectively. The MBM and HFM had significantly ( p < 0.05) lower amino acid ADCs than other animal protein ingredients, resulting in lower levels of protein digestion in these two terrestrial animal ingredients. The ADCs of phosphorus varied greatly among the animal protein ingredients, with the highest in PBPM (70.52%) and the significantly ( p < 0.05) lowest in MBM (37.31%). These ADCs data suggest that PFM, NFM, AKM, NSM, and PBPM can be prioritized as high‐quality protein sources and provide more accurate information for the nutrient and energy utilization of coho salmon.

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.